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Review

CiteSpace Software Visualization Analyses of the Last Thirty Years of Research on Populus euphratica

by
Xin Huang
1,2,
Ruiheng Lv
1,
Zhengli Zhou
1,
Min Fan
3,
Yinping Bai
2,3,
Yihang Ding
2 and
Gang Yang
1,2,*
1
Xinjiang Production & Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin, Tarim University, Alar 843300, China
2
School Life Sciences & Engineering, Southwest University Science & Technology, Mianyang 621010, China
3
School Environment & Resources, Southwest University Science & Technology, Mianyang 621010, China
*
Author to whom correspondence should be addressed.
Forests 2023, 14(4), 714; https://doi.org/10.3390/f14040714
Submission received: 16 February 2023 / Revised: 17 March 2023 / Accepted: 22 March 2023 / Published: 31 March 2023
(This article belongs to the Special Issue Restoration and Monitoring of Forested Wetlands and Salt Marshes)
Browse Figures
Versions Notes

Abstract

:
Populus euphratica is the only tall tree species that adapts to the desert environment. It has strong drought tolerance and is the subject of extreme concern at home and abroad. After 30 years of development, the scope of research on Populus euphratica is very extensive, but the research content has not yet been crystalized into a mature field, and research directions at home and abroad differ. In this study, we retrieved research references on ‘P. euphratica’ published from 1992 to 2022 in both the China National Knowledge Infrastructure core journals database and the Web of Science core collection database, and CiteSpace software was employed to conduct keyword-centered bibliometric analysis in both the spatial and temporal dimensions. The purpose of this study is to clarify the research areas, developmental changes, differences between domestic and international research priorities in the last 30 years, and future trends in the field of P. euphratica research. The results show that there were 1619 domestic papers published in China related to the field of P. euphratica research, while there were only 656 foreign papers in the same field. The development of domestic P. euphratica research went through three stages initiation (1992–2000), growth (2001–2008) and stability (2009–2021), whereas no significant international trend change was observed. The domestic disciplines focus on biology, while international research focuses on crop science. In terms of content, domestic research focuses on sustainable uses of P. euphratica forests and their response to drought, intending to improve P. euphratica ecosystems. International research, on the other hand, focuses on revealing mechanisms of environmental stresses, including genetic and physiological–morphological characteristics, to exploit the excellent characteristics of P. euphratica to serve agriculture and other fields. The development process of P. euphratica research in the past 30 years has generally evolved from an initial focus on its natural conditions towards the study of the relationship between environmental factors and P. euphratica physiological and morphological characteristics and, finally, the study of stress tolerance mechanisms and gene expression of P. euphratica. There is a trend towards ‘applications of P. euphratica tolerance genes’, which may represent a direction for future growth research.

1. Introduction

Populus euphratica (P. euphratica) is an ecologically valuable forest tree species that inhabits desert areas, presenting both a sand-anchoring capacity and a high tolerance to drought and wind conditions [1]. The global area of P. euphratica forests totals 648,000 hm2, with a geographic range spanning six climatic regions [2]. From a country distribution perspective, China hosts 58.9% (382,000 hm2) of the total P.euphratica area [3]. This forest species is also present in countries of west Asian (Iran, Iraq, Syria, and Turkey), as well as Pakistan, India, and Kazakhstan; beyond Asia, it is also present in Spain, Morocco, Kenya, and across other countries. In general, P. euphratica in these countries spans 110° longitude and is distributed along rivers [4].
In China, the Tarim Basin, located in Xinjiang, hosts an area of P. euphratica accounting for 89.1% of its total area in the country. The distribution pattern of the P. euphratica population in Tarim is aggregated distribution [5]. Due to differences in landform, water conditions and salinization, P. euphratica presents an aggregated distribution in the Tarim Basin [6], which is mainly structured into (a) the floodplain, (b) the alluvial plain, (c) salinized lands at the lower part of the fan margin and (d) the ancient riverbed located within the desert hinterland. For example, the ecological environment type around the Taklimakan Desert is mainly (d), while that around the southern slope of the Tianshan Mountains is (c) [7].
During the mid-20th century, the middle–lower reaches of the Tarim River experienced vegetation loss, desertification and general environmental degradation due to demographic growth and expanding demands for water resources and arable land. In the early 21st century, the Chinese government established several P. euphratica reserves in Xinjiang [8]. Since then, international research on P. euphratica has substantially increased, in particular in relation to the microbial resources of P. euphratica [9].
For example, Zilaiguli Mijiti et al. extracted 22 strains of bacteria from 3 samples of P. euphratica soil, water and secretion from 6 different genera in 2005 [10]. Elken Hehman et al. extracted a total of more than 190 bacterial strains from P. euphratica forest soil in the Kiyikgu River Basin in Xinjiang, 34 of which had genes with novel sequences [11]. Due to its geographical constraints, there are much fewer international reports on microorganisms in P. euphratica; only in 2012 did Martin Unterseher et al.’s study 53 endophytic fungi of 35 taxa, which were isolated from P. euphratica leaves by diversity analysis [12].
In China, research on P. euphratica more often focuses on the physiological and morphological responses to drought, among other environmental stresses. Under drought conditions, P. euphratica leaf stomatal density increases, while stomatal length diminishes, resulting in improved water retention, a physiological response that is stronger in male plants than that in female plants [13]. On the other hand, at high-salinity concentrations, P. euphratica can actively exclude Na+ from root tissue and cells via the Na+/H+ antiport system [14]. Under more extreme conditions, stem morphological changes are less pronounced in P. euphratica, and gene regulation becomes the major driver of physiological changes. For instance, under abscisic acid stress, P. euphratica regulates stem growth through a miRNA-mediated pathway that controls the hormone signal (ABA) [15].
Relative to the research work carried out in China, international research has more often been focused on transition zones of desert oases, using hyperspectral remote sensing and physiological indicator techniques applied to natural P. euphratica formations [16]. Iqbal, Arshad et al. employed hydrophilic remote sensing to estimate regional soil moisture [17] and studied transcriptomes of heteromorphic leaves and hydrophilic roots, which they applied to tobacco [18]. Moreover, Mofidabadi, AJ et al. tested the adaptability of two hybrid ‘Mofide‘ clones and their hybrids and Populus alba L. (Kaboodeh) as local clones at the Rasol Abad saline soil research station in Iran [19], where P. euphratica is mainly distributed in the southwest riparian forest and mostly used for economic cultivation [20].
Overall, it seems that although the research subjects and locations of P. euphratica are roughly the same at home and abroad, the contents and focus differ between research carried out in China and conducted internationally. Therefore, a systematic analysis of P. euphratica is very much needed to (1) compare domestic and international differences in P. euphratica research and (2) compare the research priorities between different time periods. In this study, we used the CiteSpace tool to conduct a comprehensive review of the topic.
CiteSpace is a software developed by Dr. Chen Chaomei, which is capable of visualizing bibliometrics and literature parameter information. It is simple to operate and easy to understand [21,22]. Here, CiteSpace is employed for data processing and then for visualizing information from bibliometric results. It assists us in detecting the current research priorities and frontier directions in P. euphratica forests, and also in outlining the general research trends on P. euphratica for reference of the specialized reader.

2. Data Sources and Research Methods

2.1. Data Sources

To ensure the comprehensiveness of this review, data were collected from the internationally recognized authoritative database Web of Science (WoS) Core Collection TM, the authoritative database China National Knowledge Infrastructure (CNKI), and two Chinese core journal databases: Peking University Core and CSSCI (Chinese Social Science Citation Index). Ever since the ecological significance of P. euphratica began to attract attention from various sectors in the early 1990s, the research fields of P. euphratica have been developing unprecedentedly until today. Taking this into account, first, we have set the search window for the 1992–2022 period [23], while we have used “P. euphratica” as the key search term for research reference retrieval. Second, research results were de-duplicated and sorted, resulting in 1619 Chinese and 656 English documents. Third, the screened papers were downloaded and saved in the format of “Refworks” as sample data for analysis.

2.2. Research Methodology

In this paper, we analyzed information visualization through the CiteSpace software (V.5.8.R3), using the node intensity defaults of cosine plus within slices for mapping analysis, and selecting options such as subjects, country and keyword. The “critical path” algorithm is used to obtain both metric data (i.e., number of articles, keyword frequency and centrality) and visual knowledge graphs; Excel is used to perform the statistical processing of metric data; meanwhile, analytical inference is performed in conjunction with knowledge maps to assess the research status, development history, development frontier, and trend of P. euphratica research [23].

3. Results and Analysis

3.1. Number of Publications and Disciplines

The analysis of varying patterns in publication frequency (i.e., the number of articles per year) can reveal the rates of development and changes within a specific field. Based on the Chinese database statistics of papers published each year in the multiple research fields of P. euphratica, there were a total of 1619 references published in CNKI core journals from 1992 to 2022. China Desert, Resources and Environment in Arid Areas, and Journal of Ecology were the top three journals, having published 114, 112, and 86 papers, respectively. The varying pattern of the number of articles published in CNKI (Figure 1) showed a stable trend from 1992 to 2000, when the number of publications in this field was still small, indicating that this period was just the starting stage.
From 2001 to 2008, the number of publications began to increase year by year, with an average growth rate of 30.37%, indicating that this period presented a logarithmic growth stage; the field of P. euphratica research had by then received growing attention from scholars; the enthusiasm for this research field had continuously increased; and the research base had gradually been formed and established. According to the published data, 2001 was the foremost year of severe shrinkage in China’s P. euphratica forest space since 1950 [24]. Since this year, the Chinese government and academia have increasingly focused on P. euphratica. For example, with the strict enforcement of grazing prohibition in P. euphratica nature reserves, since 2001 the first water-diversion projects and river conservation programs were launched, providing water to areas with severe declines of P. euphratica and a starting point for water conservation management [25].
From 2008 to 2021, the growth trend began to stabilize, and the change in the number of publications showed a high variation level, so this was a fluctuation stage. Within the whole past 30-year period, the domestic literature on P. euphratica had reached the highest cumulative publication frequency during this fluctuation stage, with a total of 1186 articles, accounting for 73.26% of the total number of articles published between 1992 and 2022.
Based on the WOS international database, a total of 656 English-language papers were published between 1992 and 2022; the Forests journal had the highest frequency of articles on the subject (24 articles). Concerning the period of publication between 1992 and 2006, there was no relevant English literature recorded in the WOS database. The period ranging from 2007 to 2022 can be further divided into two stages, with 2013 as their inflection point and dividing year. The 2007–2013 period can be essentially considered the initial stage of research on P. euphratica, during which there were a small number of publications, which varied slightly each year. Between 2013 and 2022, the number of publications has been rapidly increasing, accumulating 77.59% (509 articles and references) of the total number recorded during the period 1992–2022. Domestic and foreign research on P. euphratica has therefore become much more relevant in recent years. In addition, the number of papers published in 2022 in both the CNKI and WOS databases is small due to the fact that the time span of our review is not complete for 2022.
According to the domestic database, the research on P. euphratica forest in China involves 23 disciplines (Figure 2); in this review, we consider that only the disciplines with more than 10 papers are defined as mature disciplines. The top 10 disciplines in terms of the number of relevant papers are the following (ordered from highest to lowest publication frequency): forestry, biology, basic agricultural science, physical geography and mapping, agronomy, environmental science and resource utilization, plant protection, agricultural economics, automation technology, and general industrial technology and equipment. The forestry and biology disciplines, respectively, accumulate 43% and 24% of the total number of publications (among the top 10 disciplines). Furthermore, these two disciplines contain the theme of adaptation mechanisms of P. euphratica forests to abiotic stresses [26], which is the most influential and important subject in domestic research.
Within the international WOS database, there are a total of 11 disciplines involved in P. euphratica research (Figure 3), while the top 10 disciplines in terms of the number of their relevant publications are the following (also in decreasing order of publication frequency): crop science, forestry, meteorology and atmospheric sciences, phylogenetics and genomics, plant pathology, remote sensing, bioengineering, soil science, water resources and ocean dynamics. Among them, crop science and forestry accumulate the highest publication shares with 35% and 24%, respectively. These two disciplines more often contain research on groundwater levels and the sustainable use of P. euphratica forests [27], which are the most influential subjects in international research.

3.2. Key Research Countries

We use the WOS database as the research object and use centrality and burst detection statistical analysis to examine publication trends and detect their years of high research production (Table 1 and Table 2). Within the field of bibliometrics, burst detection refers to a brief and fast increase in the frequency value of a certain publication field or category (e.g., country of publication), revealing, in our case, that P. euphratica suddenly becomes a hot research topic widely tracked by scholars, academic institutions and countries. The top list of citation strengths reflects, to some extent, the countries where citation strengths are the highest in a given field.
A visual analysis of countries in the WOS database shows (Table 1) that, from highest to lowest frequency of P. euphratica research, China, Germany, the United States, Australia and Iran are the top five countries. Moreover, China has both the largest centrality and the highest number of relevant publications, indicating that China has paid more attention to P. euphratica research, which has a wide range of influence.
On the other hand, within the list of countries with high burst strengths (Table 2), China has not had strong citation years from 1992 until now, indicating that internationally China still has a low influence in this research field. As a whole, Germany has the highest strength value and its longest duration, albeit concentrated in the earliest period (2008–2011), indicating that internationally Germany has had a very high impact on the study of P. euphratica. In China, some researchers found and produced new results based on these earlier German project experiments. For instance, Cai et al. analyzed the height distribution and density of P. euphratica forest in the lower reaches of the Tarim River, employing the small-scale remote sensing method that had been used in Germany [28]. Referring to the grading standards of German forest growth and the observation value of the canopy loss degree of P. euphratica, Gurigam Miram Mamati, et al., preliminary formulated the grading standard of P. euphratica growth in the Alagan section of the lower reaches of the Tarim River [29]. In recent years, the United States and Finland have had a high strength value within the field of P. euphratica research (2020–2022).

3.3. Keyword Visualization Analysis

3.3.1. Research Hotspots

The list of keywords with high burst intensities in China (Table 3) indicates that early high-impact keywords were P. euphratica, ecological environment, Xinjiang, natural vegetation, groundwater level and Tarim River. To solve the previous context of the large-scale decline of P. euphratica forests in the lower reaches of the Tarim River, the Tarim River government launched an emergency water diversion project in 2000. The research content of this project was closely related to such keywords and mainly focused on the response of groundwater level (depth) to ecological water diversion. For example, Li et al. studied changes in groundwater levels after the fourth ecological water diversion [30], finding that P. euphratica ecosystems can benefit from a higher groundwater table, i.e., groundwater is near the P. euphratica root system when groundwater is nearby. In addition, Nuremanli et al. ecologically studied groundwater mineralization, finding that groundwater pH changes were proportional to water delivery frequency and amount [31]. These two cases above reflect that the environment of the P. euphratica ecosystem was the main theme of P. euphratica in the early stages of research.
More recently, high-strength keywords have consisted of lower Heihe, P. pruinosa, salt stress and photosynthetic characteristics, reflecting the evolution of recent research from the expansion of research sites and subjects to studying environmental factors and physiological characteristics. Photosynthetic properties have been a hot research topic in recent years and will very likely have a significant impact on P. euphratica research in the coming years. According to additional work done on centrality analysis, other important P. euphratica hub subjects are: research on restoration or prediction after ecological water diversions in the lower reaches of the Tarim River in Xinjiang; groundwater evapotranspiration of desert riparian forests; and influences of river ecological water diversions on vegetation physiology [26].
At the international level (Table 4), the early hotspots of P. euphratica research mainly consisted of transportation, stress and sodium. From 2013 to 2015, the hot keyword Xinjiang appeared when the Chinese region of Xinjiang became the main area of international research on P. euphratica. In recent years, the relevant research keywords have been climate change, riparian forest, groundwater depth and Tamarix ramosissima, revealing that research on P. euphratica is moving again towards the ecological environments of P. euphratica (and is not limited to the P. euphratica species itself). Consequently, other plants affecting P. euphratica’s growth and development are now also involved in its research.
Looking at the high strength value and high outbreak duration (Table 4), transport is the keyword with the greatest impact and the longest duration in the early research of P. euphratica. Although climate change has become an important keyword in the later period, the focus of the early research was on the physiological mechanisms of P. euphratica in salt tolerance, and drought tolerance which, furthermore, are closely related to water transport in P. euphratica. In the more recent stage, the main theme focuses on how climate change causes desertification and how it also challenges biodiversity goals. At present, the ecological value of P. euphratica is particularly prominent, e.g., the tolerance of the P. euphratica ecosystem to extreme drought along the desert coast [32,33].

3.3.2. Co-Occurrence of Keywords

Keywords can be used to summarize basic literature content, clarify research topics, and identify hotspots [34]. They are also used as node types to create keyword co-occurrence (visualization) maps, whereby node size represents the number of publications involved (by the corresponding keywords) and the connections between the nodes reflect the development branches and relations within the research field [35].
A total of 835 nodes and 1344 connections were identified in the co-occurrence graph of the CNKI knowledge network (Figure 4); the highlighted sizes of the main nodes are, in order of importance: P. euphratica, Tarim River, ecological water transportation, groundwater level, Xinjiang arid area, drought stress, lower reaches of Heihe, photosynthetic characteristics, Populus pruinosa Schrenk, salt stress, plant community and environmental factors. These keywords, along with the densely distributed connections, summarize the subjects and main contents in the research field of P. euphratica. In addition to the highest frequency of the research subject, P. euphratica, the Xinjiang Tarim River has the highest frequency, reflecting that P. euphratica research in China is mainly done in the Tarim River Basin. The long course of the Tarim River has facilitated increased mineralization and salinity of its waters, environmental conditions against which the tolerance of P. euphratica is strong. Therefore, in the Tarim River, P. euphratica has a competitive advantage compared to the rest of the vegetation, resulting in the formation of a cluster distribution pattern; this is particularly the case in the downstream area of the Tarim River, where the level of aggregation is the greatest [36]. The size of the remaining nodes and the connecting lines reveal the fact that ‘research related to the ecological restoration of P. euphratica from the perspective of water use’ is a key research priority in China [37].
Based on our analysis of the English reference database, there are 458 nodes and 1695 connections in the co-occurrence graph of the WOS knowledge network (Figure 5). Herein, the largest node corresponds to the keyword P. euphratica, which obviously identifies this tree species as the main biological subject of research. Other important nodes are downstream of the Tarim River, growth, plant, vegetation, Arabidopsis thaliana, tolerance, abscisic acid, gene expression, etc. The nodes of gene expression and salt stress are closely interlinked, indicating that P. euphratica gene expression is highly correlated with salt tolerance mechanisms. Chen et al. found that the expression of the PeDREB2 gene in P. euphratica was induced by salt stress [38], thereby the overexpression of this gene significantly improved the salt tolerance of transgenic tobacco. Furthermore, the densely distributed connection lines among abscisic acid, stomatal conductance, drought and stress indicate that P. euphratica improves salinity tolerance under drought stress by regulating abscisic acid (ABA) content, which affects stomatal conductance [39]. Overall, using the English database node size analysis, we found that the research site of P. euphratica was mainly based in the Tarim River, Xinjiang, while the research contents were mainly focused on the study of the mechanisms related to salt tolerance and drought tolerance of P. euphratica.

3.3.3. Cluster Analysis of Keywords

Keyword clustering can reflect the relevance of each keyword from the knowledge map, showing those major research clusters that have been formed within a certain technological or subject area. The serial numbers of clusters indicate the numbers of their members, starting from 0, with the serial numbers being inversely related to the members contained inside clusters, i.e., the smaller the serial number, the more members the cluster has, and the larger size it presents.
The keywords of the CNKI database were thus clustered (Figure 6) into 12 topics, from ‘#0′ to ‘#11′, with the first six clusters forming the core of the research contents. These include ecological processes related to the ecological water demand of the P. euphratica forest, i.e., the relationship among groundwater and soil water factors, the natural vegetation, P. euphratica growth and community structure of the riparian P. euphratica forest [40]. Research themes also involve P. euphratica germplasm resource conservation [41], the effects of water level, salinity and forest age on P. euphratica growth and development, and the photosynthesis and seed germination of P. euphratica [42,43]. The remaining 6 clusters (out of a total of 12) addressed the following topics: drought stress effects on the root-to-crown ratio, xylem hydraulic conductivity and embolism characteristics of P. euphratica [44,45]; population characterization and dynamics of P. euphratica forests located in the Tarim River’s mainstream [46]; soil microbial distribution patterns in P. euphratica forests and the feedback effect of P. euphratica growth and development on soil physicochemical properties [26]; and the role of P. euphratica pepex11 gene in regulating the antioxidant capacity of Arabidopsis thaliana under salt stress [47].
The keywords contained in the WOS database were primarily divided into 12 clustering topics (Figure 7), which were also divided into 2 major clusters (i.e., based on the topics and nodes of the 12 individual clusters).
The first major cluster covers #8, #9, #10 and #11 clusters, containing research that deviates from their main body, so there is no color block formation. We found that this type of research subject was more focused on micro-scale processes, dealing with the mechanism of P. euphratica, and was less related to the main topic of research. Taking #8—Arabidopsis thaliana—as an example, most of the research here was applied to the genes responsible for stress tolerance in P. euphratica. For example, Wang JunYing et al. successfully isolated the stress response gene PeNAC1 in P. euphratica subjected to salt stress; in another study, the overexpression of PeNAC1 in transgenic Arabidopsis thaliana showed stronger salt tolerance [48].
The second cluster of the English database is distinguished by its distinct and interlocking color blocks, presenting close inheritance and derivation relationships. Here, the primary focus of P. euphratica forest research, which includes #0, #1, #2, #3, #4, #5, #6 and #7 clusters, consists of the understanding of the eco-physiological principles in water utilization by P. euphratica [49,50], and that of the physiological performance mechanisms of P. euphratica under extreme conditions [51,52]. Research of this kind mainly deals with relative macrotopics involving a wide range. For instance, in #0 NaCl, the research includes both genetic genes, such as the transcriptome expression analysis of Populus talassica x P. euphratica under salt stress [53], and physiological research, such as the changes measured at the plasma H+-ATPase membrane under salt treatment [54]. Overall, the relationship among these topics is much broader, and the range of keyword expansion is large.
The keyword timeline diagram is a refined cluster map that can visualize changes in research topics reflecting the evolution of a certain field [55]. Although the clusters covered by the vertical axis of a keyword timeline diagram have the same meaning as in cluster mapping, the key innovation of the keyword timeline diagram is that the keywords of each category are then simultaneously distributed in the time series (horizontal axis) [56]. Given that the timeline diagrams of the two Chinese and English databases have similar overall distribution trends, based on the distribution of the nodes and the connecting lines of the two lines in the timeline diagrams (Figure 8 and Figure 9), the two databases of CNKI and WOS can be divided into three stages of time. The first stage has a small number of nodes with a large area that contains few topics, revealing that research at this stage is focused on a few keywords, and their research dimensions fit well into macro-scale categories. At the second stage, the numbers of nodes proliferate, the areas of their individual nodes decrease, and the interconnection lines between nodes are densely distributed, covering all topics. The research breadth of each topic increases at this stage. At the third stage, the numbers and areas of nodes decrease, while the vertical interconnecting lines are sparsely distributed, underscoring that there is less correlation between the themes, and the research of P. euphratica, therefore, tends to be more specialized at this stage.
In the timeline diagram of the CNKI database (Figure 8), there are three phases, i.e., 1992–2002, 2002–2012 and 2012–2022. The themes of the first phase (1992–2002) were mainly P. euphratica, P. euphratica forest and forest age, involving a more macroscopic dimension. Further, the keywords at this phrase were frequently linked with the nodes at the subsequent (second and third) phrases, indicating that posterior research started at this stage. For example, this is the case with research on the ecological significance, economic benefits, growth locations and ecological evolutions of P. euphratica. Pang Guangchang et al. investigated the desertification, origin and evolution trend of P. euphratica in Xinjiang [57,58], as well as the structure, distribution and geographical landscape of P. euphratica and other ecosystems in the autonomous region [59]. By 1999, the focus of P. euphratica research was on the Tarim River in Xinjiang, and more specifically, on analyzing the relationship between groundwater level and P. euphratica growth and also envisaging sustainable management projects for the species [60,61].
The second phase (2002–2012) focused on the morphological and physiological characteristics of P. euphratica, such as the linkage between photosynthesis and transpiration in P. euphratica [62], the influencing factors involved in the leaf shape index [63], water and soil factors [64] and probiotics suitable for P. euphratica growth [65]. The third phase (2012–2022) specialized on the species’ genetic and ecological characteristics and their interactions with P. euphratica [66]. For instance, soil moisture and humid environments attracted research on the physiological and ecological mechanisms of this species [67,68]. Other micro-level subjects consisted of P. euphratica population genetic structure [69], and signal transduction [70].
Within the English database, the timeline chart of WOS (Figure 9) also contains three phases, i.e., 2007–2012, 2012–2016 and 2017–2022. The first phase (2007–2012) focused more generally on the physiological and genetic characteristics of P. euphratica as manifested in water uptake and related salinity stress, involving: the significance of P. euphratica roots for hydraulic uplift; the utilization of NaCl by water uptake [71]; the regulation of abscisic acid (ABA) and CaM on gas exchange in P. euphratica leaves under salt stress [72]; and, finally, the expression of relevant genes affecting P. euphratica stress tolerance [73]. The second phase (2012–2016) focused on the morphological characteristics of P. euphratica as manifested in morphologies affecting the root-to-crown ratio of its seedlings, involving: the effects of light on morphologies and the root-to-crown ratio of its roots [74]; the effects of water environments on the role of its root growth and conformation [75]; and factors associated with seedling growth and conformation affecting its survival [76]. The third phase (2017–2022) of research focuses on ‘mechanisms that affect environmental conditions on P. euphratica and its ecosystems’ [77], such as the effect of adequate light on the germination rate of P. euphratica seeds [78] and the mechanistic relationship between soil moisture and the influence of the hydrological terrain on both physiological and ecological mechanisms that intervene in P. euphratica growth [79]. For example, P. euphratica growth is influenced by both soil moisture and wet geography [80].
The time zone view produced in CiteSpace is a further simplification of the timeline diagram, which reflects keyword evolution during the past 30 years, highlighting the varying profiles of keyword nodes and their corresponding connecting lines (for the whole period of this review).
The time zone view produced in CiteSpace is a further simplification of the timeline diagram, which reflects keyword evolution during the past 30 years, highlighting the varying profiles of keyword nodes and their corresponding connecting lines (for the whole period of this review) [81,82], such as the general research field and its location, and advancing the research significance and ecological value of P. euphratica [83,84]. The keywords of mid-term research were environmental factors (Figure 10), photosynthetic characteristics, community, litter, etc. At this mid-term, themes aimed at the influencing factors of P. euphratica growth [85,86], including: genetic variation and propagation techniques in P. euphratica [87,88], environmental water regulation [89,90], biodiversity and community structure [91,92], and studying fluid flow and meteorological factors [93]. The number of keywords in the later term was large, but the frequency was small. Only sub-sources appeared in 2016. These later studies have more specifically focused on the eco-physiological mechanisms associated with P. euphratica, such as: the new compound of P. euphratica, 2-(4-hydroxy-3-methoxyphenyl)-2-oxoacetamide [94], and stomatal regulation and constriction processes in P. euphratica leaves [95].
In general, research on P. euphratica initially focused on its natural conditions. The study of the adaptation mechanisms of the physiological and morphological characteristics of P. euphratica and environmental factors and mechanisms associated with stress tolerance under abiotic stresses would gradually transfer, later on, to the study of the physiological and morphological characteristics of P. euphratica. In contrast, the keyword evolution of the WOS time zone view was neatly inherited and continued (Figure 11), the overall research trend in WOS having shifted from a mechanistic inquiry into the impact factors of P. euphratica [96] into the research of the sustainable utilization of P. euphratica genes and ecology [73]. Therefore, the exploration of mechanisms affecting P. euphratica tolerance and its application may become a growing point of future research. As a consequence, the exploration of mechanisms affecting P. euphratica tolerance and its application may become a new turning point for future research.

4. Conclusions and Suggestions

The CNKI and WOS databases, which represent national and international perspectives, have been carefully examined. The analysis from an international perspective gives a broader scope and a more accurate understanding of P. euphratica research. In contrast, China presents the world’s sole remaining untouched natural P. euphratica forests, which are facing an area-reduction crisis [7,97]. This makes China’s research on P. euphratica occupy a key position in the world; as a well-known database in China, CNKI has important research significance. In this review, we have provided an integrated and comparative assessment of these two databases, making the most comprehensive and systematic analysis of P. euphratica research developments and changes over the past 30 years. Table 1 shows that China prioritizes research on P. euphratica, albeit its research on this subject still has low influence, so there is space for research impact development, whereas the opposite is true of other countries such as Germany and Finland.

4.1. Historical Research Evolution

Although the global forest area of P. euphratica is small, the great majority of its formations suffer from harsh environmental conditions. It is under these constraints that P. euphratica reveals its strong resilience. Its eco-physiological mechanisms are of high research value, despite research on these processes having undergone a dynamic evolutionary process. In the 1990s, P. euphratica research began to attract the attention of environmental researchers, in the context of P. euphratica area shrinkage [97]. By that time, research was more oriented towards ecosystem conservation, addressing the species’ sustainable management. The species population structure was a hot topic then. In the early 21st century, the Tarim River in Xinjiang had already become the focus of global research. Year by year, the research content has become more extensive through the study of the effects of environmental factors on the morphology and physiology of P. euphratica. From the perspective of the individual development stage, P. euphratica is a photophilic tree species, i.e., seeds can germinate rapidly at high temperatures of 35–40 degrees Celsius under full light, and the survival rate is as high as 90%; the phototaxis of P. euphratica is very strong, so its growth changes with light conditions [86,87,88]. On the other hand, a small amount of research on drought tolerance and salt tolerance began to appear by the turn of the 21st century.
From a morphological point of view, the leaves of P. euphratica form a thick, leathery layer that is very hard, and their surface is covered with wax; the twigs also present wax and short villi. These characteristics are conducive to the dissipation of strong light radiation, which is reflected by the leaves, reducing the surface temperature of the leaves, and thereby playing an important role in preventing transpiration and the burning of the leaves [98]. In the last decade, there has been a higher popularity of research on the subject, with research contents becoming more extensive, especially on the water-use mechanisms of P. euphratica under drought and salt stresses. In fact, despite the topics having somehow become less innovative (much research has been devoted to the former theme of P. euphratica environmental factors), there are two important areas where new insights are emerging.
The first area focuses on the mechanisms linked to the physiological characteristics of P. euphratica, among which the photosynthetic properties of P. euphratica play a key function in most of the physiological mechanisms. For instance, Su et al. have shown that exogenous plant growth factors can regulate photosynthesis in P. euphratica, alleviating salt stress; Shi et al. have revealed the link between leaf water potential and photosynthesis; and Chen et al. have also found the key role of photosynthesis in drought tolerance in P. euphratica [98,99,100].
The second area of research is centered on P. euphratica stress-tolerance genes. Under low groundwater levels, P. euphratica is capable of maintaining a stable internal water environment by regulating its own physiological and biochemical mechanisms, and so it prevents damage from drought. At the moment, new research is being done on the drought tolerance mechanisms of P. euphratica by screening and verifying the functional-coding genes, which intervene in processes such as ion transport, antioxidant enzymes, signal transduction, and other mechanisms linked to stress transcription factors. In this regard, Jiao et al. have analyzed the short-term transcriptome response of P. euphratica roots and leaves to drought stress [101]. Overall, the research profile attained during this period concludes that P. euphratica can adapt to harsh environments via the regulation of tolerance genes that alter the physiological morphology of P. euphratica, especially that of P. euphratica leaves, being so closely related to photosynthesis. Furthermore, in recent years, new applied research built on previous authors’ contributions has begun to take shape; for example, Han et al. have improved tobacco drought tolerance by transcribing the XTH drought tolerance gene of P. euphratica [102]. Within the wide field of gene applications, virus-induced gene silencing techniques have been brought to the forefront of new research developments.
In summary, the overall trend has turned from macro-scale to microscopic research, i.e., from initial topics focusing on the study of natural conditions, towards linkages between environmental factors and physiological and morphological characteristics of P. euphratica. The latest research has gradually refined to incorporate P. euphratica tolerance and gene expression mechanisms, whose potential research may mark the beginning of a future trend focused on ‘applied research on P. euphratica tolerance genes’.

4.2. Spatial Research Differences

P. euphratica is the oldest tree species in the genus Populus. It has important value for the study of climate change, river change, flora evolution and cultural development in the desert area of Northwest China [103]. Due to cultural differences, the research interest in P. euphratica abroad is only reflected in the application of its special physiological mechanisms [104]. At any rate, whether at home or internationally, the processes of P. euphratica that regulate environmental stress have always been at the center of attention [105]. For example, Wang Yeli et al. analyzed the cis-acting elements of PeDREB2A and PeWRKY19 gene promoter sequences of P. euphratica by means of bioinformatics and transient expression of GUS transgenic tobacco [106]. Zeng Ming et al. revealed the molecular regulation mechanism of leaf morphology and physiological changes in P. euphratica by analyzing the differentially expressed miRNAs and their target gene functions in heteromorphic leaves of P. euphratica [107]. These studies have shown how P. euphratica genes improve stress tolerance by affecting its physiological morphology. At this point, however, the following question merits the advancement of new research work, i.e., which are the trigger-factors for gene regulation? Foreign scholars Brosche, Mikael et al. found that the expression of P. euphratica genes is stimulated by environmental stress, and this would help it adapt to environmental changes. In their view, the P. euphratica genome itself does not contain meaningful differences, so instead it would be the regulation of gene expression that explains its strong resistance [108]. However, domestic scholars Chu Chenchen and other researchers have found that there are indeed a large number of chromosome rearrangements in the genome of P. euphratica, such that it adapts to environmental stress, which is therefore associated with the diversity of gene regulation [109]. Therefore, a systematic review of these types of diverging conclusions—even before the same performance—is required to identify the research niches that are still in need of confirmation. Here, this phenomenon is mentioned from the sole perspective of P. euphratica gene research.
Similarities and differences between domestic and international were examined from three perspectives: basic contexts, research priorities, and development trends. It was found that domestic research in China began earlier than international research; this has been reflected in a clear trend in publication numbers. In 2007, research on P. euphratica was not only conducted domestically but had already attracted wide international attention and frequent cooperation among institutions in various countries. To name a few, the Erie State Forestry Institute of China and the Almaty Institute of Animal Husbandry and Veterinary Steppe Plants of the Ministry of Agriculture of Kazakhstan held relevant discussions on the ecological problems of P. euphratica [110], while German and Japanese researchers studied P. euphratica root growth and biomass distribution in the lower Aral Sea basin of the Amu Darya River [103].
Domestic research in China involves more diverse research disciplines than international ones: China’s research priorities are more directed toward biology, whereas the latter is more focused on crop science. In this review, keywords were employed to analyze research contents, so our comprehensive keyword analysis (Figure 4 and Figure 5) demonstrates that both domestic and international research were focused on P. euphratica drought tolerance, with their main research site located in Xinjiang’s Tarim River. The difference between domestic and international research is that research in China has often focused on the status of groundwater tables and the ecological water transfer of P. euphratica to solve drought problems, whereas international research has frequently focused on genes and the drought tolerance mechanism of P. euphratica. From the perspective of changes in attractive research areas, research on the ecological environments of P. euphratica had received both domestic and international attention, although at different times. The time for domestic research was 1995–2006, anticipating more than two decades for international research, whose main activity developed during the period 2018–2022. It is undeniable that domestic research has also become more integrated with the realities of China.
In summary, there are different situations and starting points for domestic and international research. International research is aimed at utilizing the characteristics of P. euphratica to benefit agriculture and other aspects, whereas domestic research is aimed at improving P. euphratica ecosystems themselves. There is still a gap in breadth and depth between domestic and international research, with the direction of domestic research being closely linked to the real-time problems occurring in the P. euphratica ecosystem (changes in the P. euphratica ecosystem), so the subject matter of domestic research is thus more suited to the necessities for P. euphratica ecosystem improvement. In the future, domestic research in China should focus more on their micro-scale processes and increase the employment of quantitative methodologies. On the other hand, international research should increase its discipline coverage and improve the systematics of research analyses. Scholars are well aware of the application values of P. euphratica in both domestic and international research, and more and more scholars are conducting applied research on the results of the tolerance mechanism of P. euphratica [111].

Author Contributions

Conceptualization, X.H. and G.Y.; methodology, G.Y.; software, X.H.; validation, Y.B. and M.F.; formal analysis, Z.Z.; resources, R.L.; data curation, Z.Z.; writing—original draft preparation, X.H.; writing—review and editing, G.Y.; visualization, Y.D.; project administration, R.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Xinjiang Production and Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin (BRZD1901), the major science and technology project plan of Xinjiang Production and Construction Corps (2021AB022).

Data Availability Statement

The data that support the findings of this study are open access in [China National Knowledge Infrastructure].

Acknowledgments

We sincerely thank Gutierrez Rodriguez Lucas for his full assistance with English words and grammar problems in the manuscript. Thanks to everyone who contributed to the manuscript and to everyone in the lab for their help.

Conflicts of Interest

No potential conflicst of interest was reported by the authors. Grantees have no role in the program.

References

  1. Yi, X.; Wang, N.; Deng, A.; Elken, R. Selection of dominant Populus euphratica varieties and construction of genetic markers in low groundwater level area of Tarim River Basin. J. Plant Genet. Resour. 2006, 3, 3359–3362. [Google Scholar]
  2. Yang, Y.; Yan, Z. Correlation analysis between geographical distribution characteristics of Populus euphratica and climate environment. Anhui Agric. Sci. 2012, 40, 12483–12486. [Google Scholar]
  3. Zhang, N.; Li, B.; Xu, T.; Wang, J. Temporal and spatial variation characteristics of drought index in global Populus euphratica distribution area from 1960 to 2012. Resour. Environ. Arid. Areas 2017, 31, 121–126. [Google Scholar]
  4. Saborowski, J.; Marx, A.; Nagel, J.; Böckmann, T. Double sampling for stratification in periodic inventories—Infinite population approach. For. Ecol. Manag. 2010, 260, 1886–1895. [Google Scholar] [CrossRef]
  5. Han, L.; Wang, H.; Zhou, Z.; Li, Z. Population structure and statistical analysis of Populus euphratica in the upper and middle reaches of Tarim River. Ecology 2007, 4, 1315–1322. [Google Scholar]
  6. Yan, G.; Lu, P. Prospects for the future development of forests in Xinjiang. For. Xinjiang 1987, 5, 55–62. [Google Scholar]
  7. Wang, S. Global current status and protection and restoration countermeasures of Populus euphratica. World For. Res. 1996, 6, 38–45. [Google Scholar]
  8. Xia, Z.; Chen, Y.; Zhu, C.; Zhou, Y.; Chen, X. Stomatal changes in leaves of P. euphratica under drought stress. Res. Arid. Areas 2018, 35, 1111–1117. [Google Scholar]
  9. Sun, J.; Chen, S.; Dai, S.; Wang, R.; Li, N.; Shen, X.; Zhou, X.; Lu, C.; Zheng, X.; Hu, Z.; et al. NaCl-Induced Alternations of Cellular and Tissue Ion Fluxes in Roots of Salt-Resistant and Salt-Sensitive Poplar Species. Plant Physiol. 2009, 149, 1141–1153. [Google Scholar] [CrossRef] [Green Version]
  10. Mijiti, Z.G.; Xiangru, M.; Dureyimu, A.A.; Todahun, M.; Abaidula, G.; Rehman, E. Ecological distribution of culturable bacteria in natural Populus euphratica woodlands of Tarim River. Biotechnology 2009, 19, 19–22. [Google Scholar]
  11. Hehman, E. Study on bacterial diversity in natural Populus euphratica of Kiyik, Xinjiang. Xinjiang Agric. Sci. 2016, 53, 921–934. [Google Scholar]
  12. Unterseher, M.; Petzold, A.; Schnittler, M. Xerotolerant foliar endophytic fungi of Populus euphratica from the Tarim River basin, Central China are conspecific to endophytic ITS phylotypes of Populus tremula from temperate Europe. J. Fungal Divers. 2012, 54, 133–142. [Google Scholar] [CrossRef]
  13. Lian, C.L.; Yao, K.; Duan, H.; Li, Q.; Liu, C.; Yin, W.; Xia, X. Exploration of ABA Responsive miRNAs Reveals a New Hormone Signaling Crosstalk Pathway Regulating Root Growth of Populus euphratica. Int. J. Mol. Sci. 2018, 19, 1481. [Google Scholar] [CrossRef] [Green Version]
  14. Sohrabi, H.; Parsapour, M.K.; Soltani, A.; Iranmanesh, Y. Early differentiation in biomass production and carbon sequestration of white poplar and its two hybrids in Central Iran. J. For. Res. 2015, 26, 65–69. [Google Scholar] [CrossRef]
  15. Lu, W. For the magnificent Populus euphratica—Inner Mongolia Autonomous Region, Alxa League, Ejin Banner Forest Public Security Bureau, Populus euphratica protection work patrol. For. Public Security. Bur. 2012, 6, 12–13. [Google Scholar]
  16. Sun, Y.; Wan, C.; Zhang, L. Identification of soil actinomycetes and its secondary metabolites. J. Tarim Univ. 2015, 27, 1–7. [Google Scholar]
  17. Iqbal, A.; Wang, T.; Wu, G.; Tang, W.; Zhu, C.; Wang, D.; Li, Y.; Wang, H. Physiological and transcriptome analysis of heteromorphic leaves and hydrophilic roots in response to soil drying in desert Populus euphratica. Sci. Rep. 2017, 7, 12188. [Google Scholar] [CrossRef] [Green Version]
  18. Ainiwaer, M.; Ding, L.; Kasim, N.; Wang, J.; Wang, J. Regional scale soil moisture content estimation based on multi-source remote sensing parameters. Int. J. Remote Sens. 2020, 41, 3346–3367. [Google Scholar] [CrossRef]
  19. Mofidabadi, A.; Ghmeri-Zareh, A.; Salari, A. Five Years Performance of New Introduced Salt Tolerant Hybrid Poplar clones (Mofid and P. × albaeuphratica) In Iran (West Azar-Bayjan). Silvae Genet. 2015, 64, 117–120. [Google Scholar] [CrossRef]
  20. Zhang, D.; Wen, Y.; Wang, J.; Li, F.; Cai, H.; Liu, W. Physiological parameters and spectral characteristics analysis of Populus euphratica leaves under different groundwater buried depths. For. Resour. Manag. 2022, 1, 24–34. [Google Scholar]
  21. Ping, Q.; He, G.; Chen, C.M. How Many Ways to Use CiteSpace? A Study of User Interactive Events over 14 Months. J. Assoc. Inf. Sci. Technol. 2017, 68, 1234–1256. [Google Scholar] [CrossRef]
  22. Hou, J.; Hu, Z. Review and Prospect of CiteSpace Software Application Research. Mod. Intell. 2013, 33, 99–103. [Google Scholar]
  23. He, Y.; Jiang, H.; Zhang, Y.; Yang, G.; Kang, X.; Chen, H.; Wu, N. CiteSpace-based bibliometric analysis of small and micro wetlands. J. Ecol. 2022, 42, 5516–5530. [Google Scholar]
  24. Xiao, S.; Chen, X.; Ding, A. Progress in the mechanism of climate change and environmental evolution in modern Alxa desert. China Desert 2017, 37, 1102–1110. [Google Scholar]
  25. Li, L. Application of Tennant Method in Tarim River. Shaanxi Water Conserv. 2022, 4, 58–62. [Google Scholar]
  26. Wang, Y.; Long, Y.; Li, Y.; Wang, Y.; Lv, G.; Yang, J.; Gao, X.; Chang, S.; Yang, X. The relationship between the soil physicochemical properties and the space and distribution of microbial community structure. J. Ecol. 2021, 41, 5669–5684. [Google Scholar]
  27. Wei, Y.; Wang, Z.; Liang, W.; Ma, F.; Han, L. Response and adaptation of functional traits of poplar branches and leaves to groundwater level gradients. Northwest J. Bot. 2020, 40, 1043–1051. [Google Scholar]
  28. Cai, F.; Halic, Z.; Wang, J.; Adiri, A.; Abuluduman, M.Y. Height distribution and density of Populus euphratica in Alagan section of the lower reaches of Tarim River. Ecol. Environ. 2008, 17, 559–563. [Google Scholar]
  29. Maimaiti, G.M.; Khalik, Z.; Aishan, T.; Wang, J. Response of crown thinning of Populus euphratica to emergency ecological water conveyance in the lower reaches of Tarim River. Xinjiang Agric. Sci. 2010, 47, 241–245. [Google Scholar]
  30. Li, W.; Chen, Y.; Zhang, H.; Hou, P. Emergency water conveyance and vegetation response in the lower reaches of Tarim River. China Desert 2004, 24, 7–51. [Google Scholar]
  31. Ani, H.; Nur, I.; Baidugera, A.; Abduayni, K.; Haliq, Z.; Shandai, H.; Wu, T. Hydrogen and oxygen stable isotope and hydrochemical characteristics of groundwater in different habitats of Populus euphratica forest. J. Fujian Agric. For. Univ. 2021, 50, 781–788. [Google Scholar]
  32. Fu, A.; Wang, W.; Li, W.; Chen, Y. Resistance and Resilience of Desert Riparian Communities to Extreme Droughts. Forests 2022, 13, 1032. [Google Scholar] [CrossRef]
  33. Li, H.; Feng, J.; Bai, L.; Zhang, J. Populus euphratica Phenology and Its Response to Climate Change in the Upper Tarim River Basin, NW China. Forests 2021, 12, 1315. [Google Scholar] [CrossRef]
  34. Liu, J.; Wang, K. Knowledge map of domestic intelligent textile and garment field based on CiteSpace. Cloth. Des. 2022, 112–117. [Google Scholar]
  35. Li, H.; Lin, C. Keyword analysis method for scientific research results based on Time-series clustering. Sci. Res. Manag. 2022, 43, 176–183. [Google Scholar]
  36. Du, W.-H.; Guan, W.-K.; Huo, A.-D.; Liang, Y.; Yi, X.; Wei, H. Population structure and spatial distribution characteristics of Populus euphratica in the main stream of Tarim River. Hubei Agric. Sci. 2019, 58, 64–68. [Google Scholar]
  37. Peng, S.; Chen, X.; Jing, Q.; Liu, S. Spatial Pattern of Populus euphratica Change as Affected by Water Conveyance in the Lower Tarim River. Forests 2014, 5, 134–152. [Google Scholar] [CrossRef] [Green Version]
  38. Qiao, Y.; Ren, J.; Wei, S.; Chen, Y.; Wu, R. Photosynthetic physiological and ecological characteristics of the five main tree-irrigation tree species in the loess hilly area. Res. Soil Water Conserv. 2021, 28, 397–406. [Google Scholar]
  39. Zhang, X.; Wang, R.; Li, Z. Response characteristics of Populus euphratica seed germination to warm and light conditions and salt–drought stress. Northwest J. Bot. 2015, 35, 1642–1649. [Google Scholar]
  40. Wang, D. Suggestions on soil and water remediation along the western section of Tarim River in Xinjiang. Sci. Technol. Innov. Appl. 2021, 11, 124–126. [Google Scholar]
  41. Liu, J.; Li, Z.; He, L.; Zhou, Z.; Xu, Y. Studies on salt tolerance of Populus euphratica and Populus pruinosa during seed germination. For. Sci. 2004, 40, 165–169. [Google Scholar]
  42. Zhou, Z.; Yu, J.; Li, Z.; Ma, L.; He, L. Studies on the nutritional chemical constituents of seeds of Populus euphratica and Populus pruinosa. Northwest Bot. J. 2003, 23, 987–991. [Google Scholar]
  43. Xu, H.; Chen, Y.; Li, W. Response study of groundwater after ecological water transmission in the lower Tarim River. Environ. Sci. Res. 2003, 16, 19–22. [Google Scholar]
  44. Li, Z.; Jiao, P.; Zhou, Z.; Li, Q.; Li, J. Morphological and anatomical study on lateral roots and adventitious buds of Populus euphratica. J. Beijing For. Univ. 2011, 33, 42–48. [Google Scholar]
  45. Xu, Q. The xylem anatomy and hydraulic properties of A. Populus in response to drought stress. D. Xinjiang Agric. Univ. 2012, 8, 11–15. [Google Scholar]
  46. Du, W.; Guan, W.; Hoidi; Yi, X.; Wei, H. Study on the water and salt characteristics of the forest soil forest of the main stream of the Tarim River. J. Southwest For. Univ. Nat. Sci. 2019, 39, 92–99. [Google Scholar]
  47. Yao, K.; Lian, C.; Wang, J.; Wang, H.; Liu, C.; Yin, W.; Xia, X. Populus euphratica PePEX11 genes are involved in regulating the antioxidant capacity of Arabidopsis under salt stress. J. Beijing For. Univ. 2018, 40, 19–28. [Google Scholar]
  48. Wang, Y.; Wang, P.; He, Y. A Populus euphratica NAC protein regulating Na+/K+ homeostasis improves salt tolerance in Ara-bidopsis thaliana. Gene 2013, 521, 265–273. [Google Scholar] [CrossRef]
  49. Zhao, L.; Wang, L.X.; Cernusak, L.A.; Liu, X.; Xiao, H.; Zhou, M.; Zhang, S. Significant Difference in Hydrogen Isotope Composition between Xylem and Tissue Water in Populus euphratica. Plant Cell Environ. 2016, 39, 1848–1857. [Google Scholar] [CrossRef] [Green Version]
  50. Zhang, X.; Kang, E.; Si, J.; Zhou, M. Study on Water Consumption Law of Populus euphratica. J. Arid. Land Resour. Environ. 2006, 20, 195–197. [Google Scholar]
  51. Chen, S.; Polle, A. Salinity tolerance of Populus. Plant Biol. 2010, 12, 317–333. [Google Scholar] [CrossRef]
  52. Li, H.; Li, M.; Wei, X.; Zhang, X.; Xue, R.; Zhao, Y.; Zhao, H. Transcriptome analysis of drought-responsive genes regulated by hydrogen sulfide in wheat (Triticum aestivum L.) leaves. Mol. Genet. Genom. 2017, 292, 1091–1110. [Google Scholar] [CrossRef]
  53. Liu, Y.; Su, M.; Han, Z. Effects of NaCl Stress on the Growth, Physiological Characteristics and Anatomical Structures of Populus talassica × Populus euphratica Seedlings. Plants 2022, 11, 3025. [Google Scholar] [CrossRef] [PubMed]
  54. Yang, Y.; Zhang, F.; Zhao, M.; An, L.; Zhang, L.; Chen, N. Properties of plasma membrane H+-ATPase in salt-treated Populus euphratica callus. Plant Cell Rep. 2007, 26, 229–235. [Google Scholar] [CrossRef]
  55. Yang, F.; Chen, Y. Progress, application and enlightenment of sports big data in developed countries in the past 10 years. J. Xi’an Phys. Educ. Univ. 2020, 37, 385–393. [Google Scholar]
  56. Yang, L.; Shen, C. The evolution trajectory and trend prospect of tax incentives—Based on literature visualization analysis. Tax Res. 2022, 10, 82–91. [Google Scholar]
  57. Pang, G.; Wang, L.; Wang, H.; Wang, J.; Zhou, S. The genetic structure of Populus euphratica population and its relationship to the natural environment. Northwest J. Bot. 1992, 12, 295–302. [Google Scholar]
  58. Sun, X.; Kang, X. Research status and development suggestions of Populus euphratica. World For. Res. 1993, 6, 48–52. [Google Scholar]
  59. Wang, X. Changes of the ecological environment of the Silk Road in China. J. Northwest Univ. Nat. Sci. Ed. 1999, 29, 67–71. [Google Scholar]
  60. Wang, H.; Han, L.; Zhou, Z.; Li, Z. Dynamic response of water potential of Populus euphratica and Populus pruinosa to different groundwater levels. Agric. Res. Arid. Areas 2007, 25, 125–129. [Google Scholar]
  61. He, Z.; Zhao, W. Spatial heterogeneity of vegetation in typical desert riparian forest in lower Heihe River. Glacier Permafr. 2003, 25, 591–596. [Google Scholar]
  62. Cao, S.; Qi, F.; Si, J.; Chang, Z.; Chen, K.; Cao, G. Research on the relationship between Populus euphratica photorespiration and influence factors. Drought Zone Resour. Environ. 2012, 26, 155–159. [Google Scholar]
  63. Wang, Y.; Jiao, P.; Gu, Y.; Zhang, S.; Li, Z. The relationship of Populus euphratica leaf shape changes and POD isozymes. Resour. Environ. Arid. Areas 2013, 27, 181–186. [Google Scholar]
  64. Jing, J.; Xia, J.; Hao, P.; Li, J.; Feng, Y.; Tan, Z.; Yang, X. Effects of Soil Type, Water Content and Salinity on Tillering of Populus euphratica. J. Northeast. For. Univ. 2013, 41, 42–63. [Google Scholar]
  65. Yang, Y.; Chen, Y.; Cai, B.; Jie, W.; Lv, D. Isolation and identification of the mycobacterial mycorrhizal fungi in the extreme arid areas. Drought Area Geogr. 2012, 35, 260–266. [Google Scholar]
  66. Tan, S.; Ao, X.; Fu, Z.; Qin, J.; Xu, G.; Lu, M. Phenotypic analysis of transgenic Arabidopsis plants with large fragments of Populus euphratica. J. Cent. South Univ. For. Technol. 2016, 36, 53–56. [Google Scholar]
  67. Wang, H.; Lu, H.; Xu, Y.; Niu, J.; Yu, J. Effect of soil moisture gradient on photosynthesis and stress tolerance of Populus euphratica. Ecol. J. 2017, 37, 432–442. [Google Scholar]
  68. Yang, Y.; Zhu, C.; Wang, Y.; Zhou, H. Effects of ecological water diversion on carbon cycle of Populus euphratica ecosystem in the lower reaches of Tarim River. Arid. Land Geogr. 2021, 44, 637–642. [Google Scholar]
  69. Chen, X.; Gai, Z.; Zhai, L.; Xu, J.; Jiao, P.; Wu, Z.; Li, Z. Construction of the genetic diversity and core conservation unit of the natural Populus euphratica population in northwest China. Biodiversity 2021, 29, 1638–1649. [Google Scholar] [CrossRef]
  70. Zhao, R.; Chen, S. Ion balance and reactive oxygen species balance signal network regulated by salt tolerance in Populus euphratica. Chin. Sci. Life Sci. 2020, 50, 167–175. [Google Scholar]
  71. Hao, X.-M.; Chen, Y.-N.; Li, W.-H.; Guo, B.; Zhao, R.-F. Evidence and Ecological Effects of Hydraulic Lift in Populus euphratica. Acta Phytoecol. Sin. 2009, 33, 1125–1131. [Google Scholar]
  72. Zhang, Y.; Shi, Y.; Wang, R.; Chen, S.L.; Li, N.Y.; Shao, J.; Zhang, H.; Li, J.; Sun, J. Effects of ABA and CaM on Leaf Gas Exchange of Populus euphratica in the Process of Initial Salinity. Sci. Silvae Sin. 2008, 44, 57–64. [Google Scholar]
  73. Si, J.; Zhou, T.; Xu, F.; Bo, W.; Wu, R. Salt-responsive MicroRNAs in Populus euphratica by Deep Sequencing. Bull. Bot. Res. 2015, 35, 836–842. [Google Scholar]
  74. Xiao, S.; Xiao, H.; Si, J.; Xi, H. Study on the Sub-Diurnal Radial Growth of the Populus euphratica. J. Glaciol. Geocryol. 2010, 32, 816–822. [Google Scholar]
  75. Yu, B.; Zhao, C.Y.; Li, J.Y.; Peng, G. Morphological, physiological, and biochemical responses of Populus euphratica to soil flooding. Photosynthetica 2015, 53, 110–117. [Google Scholar] [CrossRef]
  76. Lv, S.; Zhang, X.; Zhang, N.; Xia, Y.; Jing, J.; Li, J. Response of Root Growth and Architecture of Populus euphratica Seedling on Soil Water. Acta Bot. Boreali. Occident. Sin. 2015, 35, 1005–1012. [Google Scholar]
  77. Zeng, M.; He, S.; Hao, J.; Zhao, Y.; Zheng, C. iTRAQ-based proteomic analysis of heteromorphic leaves reveals eco-adaptability of Populus euphratica Oliv. J. Plant Physiol. 2022, 271, 153644. [Google Scholar] [CrossRef]
  78. Li, Z.; Liu, J.; Yu, J.; Zhou, L. Populus euphratica, bioecological characteristics investigation of Populus chinensis. Northwest J. Bot. 2003, 7, 236–240. [Google Scholar]
  79. Li, D.; Si, J.; Zhang, X.; Gao, Y.; Luo, H.; Qin, J.; Gao, G. The Mechanism of Changes in Hydraulic Properties of Populus euphratica in Response to Drought Stress. Forests 2019, 10, 904. [Google Scholar] [CrossRef] [Green Version]
  80. Zhang, H.; Deng, C.; Wu, X.; Yao, J.; Zhang, Y.; Zhang, Y.; Deng, S.; Zhao, N.; Zhao, R.; Zhou, X.; et al. Populus euphratica remorin 6.5 activates plasma membrane H+-ATPases to mediate salt tolerance. Tree Physiol. 2020, 40, 731–745. [Google Scholar] [CrossRef]
  81. Zhong, J.; Guan, W.; Yi, X.; Huo, E.; Qin, Y.; Liu, D.; He, X. Physical and chemical properties of soil and its influence on growth of Populus euphratica. Soil Water Conserv. 2018, 25, 134–138. [Google Scholar]
  82. Yang, J.; Hua, G. Land desertification in Xinjiang and its prevention and control measures. Prot. For. Sci. Technol. 1998, 24–29. [Google Scholar]
  83. Li, D.; Wang, Z. Quantitative analysis of the impact of climate change and human activities on vegetation NPP in Shaanxi Province. J. Ecol. Environ. 2022, 31, 1071–1079. [Google Scholar]
  84. Zhong, J. Creating the green ecological barrier in the northwest of the motherland-Ejina forestry construction 30 years of remarkable achievements. Inn. Mong. Forestry 2008, 11, 12–13. [Google Scholar]
  85. Li, Z. Professor Zhijun Li’s team at Tarim University revealed for the first time the mechanism by which geographical and environ-mental factors drive genetic differentiation in the Populus Section. J. Tarim Univ. 2021, 33, 2. [Google Scholar]
  86. Zhou, Z.; Li, Z.; Gong, W.; Gao, S. Study on the flowering biological characteristics of Populus euphratica and Populus pruinose. Wuhan Bot. Res. 2005, 2, 163–168. [Google Scholar]
  87. Liu, J.; Han, L.; Gong, W.; Zhou, Z.; Li, Z. Comparative study on photosynthesis and transpiration of Populus euphratica and Populus pruinose. J. Tarim Agric. Univ. 2004, 3, 1–6. [Google Scholar]
  88. Li, Z.; Tian, L.; Zhang, T.; Pan, C.; Zhang, H. Study on water and salt dynamics of artificial Populus euphratica forest in summer. North. Hortic. 2010, 22, 77–80. [Google Scholar]
  89. Cao, S.; Qi, F.; Si, J.; Zhang, X.; Liu, W.; Chang, Z. Studies of vegetation and environmental factors in Ejina Oasis. China Desert 2010, 30, 172–179. [Google Scholar]
  90. Yu, Q.; Song, X.; Yang, M.; Gao, B. Study on the molecular mechanism of salt tolerance in Populus euphratica. Hebei Linguo Res. 2012, 27, 402–404. [Google Scholar]
  91. Fu, A.; Li, W.; Chen, Y.; Chen, Y.P.; Ma, J. Factor analysis of water changes in broad-ovate leaves of Populus euphratica in extremely arid areas. China Desert 2012, 32, 65–72. [Google Scholar]
  92. Lv, R.; Han, L.; Zhou, Z.; Liang, J.; Yu, J. Structural analysis of poplar communities in the middle reaches of Tarim River. China Agron. Bull. 2013, 29, 57–61. [Google Scholar]
  93. Zhao, C.; Si, J.; Feng, Q.; Yu, T.; Li, W. (Populus euphratica) Stem sap flow characteristics and its relationship with environmental factors. China Desert 2014, 34, 718–724. [Google Scholar]
  94. Luo, J.-R.; Jiang, H.-E.; Zhao, Y.-X.; Zhou, J.; Qian, J.-F. Components of the heartwood of Populus euphratica from an ancient tomb. Chem. Nat. Compd. 2008, 44, 6–9. [Google Scholar] [CrossRef]
  95. Shi, J.; Liu, M.; Wang, X.; Ma, X. Biomass and stoichiometric characteristics of dead branches of Populus euphratica at different ages. Acta Ecol. Sin. 2017, 37, 887–895. [Google Scholar]
  96. Li, D.; Si, J.; Zhang, X.; Gao, Y.; Wang, C.; Luo, H.; Qin, J.; Gao, G. Hydraulic Characteristics of Populus euphratica in an Arid Environment. Forests 2019, 10, 407. [Google Scholar] [CrossRef] [Green Version]
  97. Qi, R.; Zhao, J.; Luo, W.; Bekturhan, Y. Impact assessment of Populus euphratica in Wuerhe District based on forest disturbance degree. For. Sci. Technol. Newsl. 2020, 9, 12–17. [Google Scholar]
  98. Chen, M. Study on the drought tolerance mechanism of Populus euphratica in the middle and lower reaches of Tarim River. Anhui Agric. Sci. 2021, 49, 111–114. [Google Scholar]
  99. Su, M.; Zhang, M.; Liu, Y.; Han, Z. Abscisic Acid, Paclobutrazol, and Salicylic Acid Alleviate Salt Stress in Populus talassica × Populus euphratica by Modulating Plant Root Architecture, Photosynthesis, and the Antioxidant Defense System. Forests 2022, 13, 1864. [Google Scholar] [CrossRef]
  100. Wang, H.; Wang, D.; Shan, P.; Xiang, P.; Yang, D.; Zhao, G.; Li, S. Experimental study on drip irrigation under tobacco film. Tob. Sci. China 2011, 32, 42–46. [Google Scholar]
  101. Jiao, P.; Wu, Z.; Wang, X.; Jiang, Z.; Wang, Y.; Liu, H.; Li, Z.; Qin, R. Short-term transcriptomic responses of Populus euphratica roots and leaves to drought stress. J. For. Res. 2021, 32, 841–853. [Google Scholar] [CrossRef] [Green Version]
  102. Han, Y.; Yi, H. Overexpression of the XTH gene in Populus euphratica was able to improve tobacco drought tolerance. China, J. Biochem. Mol. Biol. 2016, 32, 919–925. [Google Scholar]
  103. Khamzina, A.; Lamers, J.P.A.; Vlek, P.L.G. Tree establishment under deficit irrigation on degraded agricultural land in the lower Amu Darya River region, Aral Sea Basin. For. Ecol. Manag. 2008, 255, 168–178. [Google Scholar] [CrossRef]
  104. Schnitzler, P.; Louis, S.; Behnke, K.; Loivamäki, M. Poplar volatiles-biosynthesis, regulation and (eco)physiology of isoprene and stress-induced isoprenoids. Plant Biol. 2010, 12, 302–316. [Google Scholar] [CrossRef] [PubMed]
  105. Popko, J.; Haensch, R.; Mendel, R.-R.; Polle, A.; Teichmann, T. The role of abscisic acid and auxin in the response of poplar to abiotic stress. Plant Biol. 2010, 12, 242–258. [Google Scholar] [CrossRef]
  106. Wang, Y.; Tang, W.; Wang, H. Stress response elements and functional analysis of DREB2A and WRKY19 gene promoters in Populus euphratica. Mol. Plant Breed. 2019, 17, 428–436. [Google Scholar]
  107. Zeng, M.; He, S.; Li, W.; Feng, J.; Zhao, Y.; Zheng, C. Functional analysis of differentially expressed miRNAs and their target genes in heteromorphic leaves of Populus euphratica. J. Beijing For. Univ. 2020, 42, 1–13. [Google Scholar]
  108. Brosche, M.; Vinocur, B.; Alatalo, E.R.; Lamminmäki, A.; Teichmann, T.; Ottow, E.A.; Djilianov, D.; Afif, D.; Bogeat-Triboulot, M.-B.; Altman, A.; et al. Gene expression and metabolite profiling of Populus euphratica growing in the Negev desert. Genome Biol. 2005, 6, 1–17. [Google Scholar] [CrossRef] [Green Version]
  109. Chu, C.; Sun, M.; Wu, Y.; Yan, Z.; Li, T.; Feng, Y.; Guo, Y.; Yin, T.; Xue, L. Pangenome construction and genome variation analysis of Populus euphratica. J. Nanjing For. Univ. 2022, 46, 251–260. [Google Scholar]
  110. Xinjiang Uygur Autonomous Region Forestry Bureau Propaganda Information Center. The Green Sea shortwave. Xinjiang For. 2007, 5, 9–14. [Google Scholar]
  111. Niu, W. DREB transcription factors and their application in plant stress tolerance breeding. Jiangsu Agric. Sci. 2014, 42, 17–20. [Google Scholar]
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Figure 1. Number of domestic and international publications on Populus euphratica recorded in the WOS and CNKI databases between 1992 and 2022. The horizontal and vertical coordinates represent the year and the number of publications, respectively. WOS is represented with blue bars, and CNKI is represented with black bars.
Figure 1. Number of domestic and international publications on Populus euphratica recorded in the WOS and CNKI databases between 1992 and 2022. The horizontal and vertical coordinates represent the year and the number of publications, respectively. WOS is represented with blue bars, and CNKI is represented with black bars.
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Figure 2. The 10 disciplines with the highest number of articles on Populus euphratica in the Chinese National Knowledge Infrastructure database. The number in each section reflects the total number of publications on P. euphratica, within a certain discipline.
Figure 2. The 10 disciplines with the highest number of articles on Populus euphratica in the Chinese National Knowledge Infrastructure database. The number in each section reflects the total number of publications on P. euphratica, within a certain discipline.
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Figure 3. The 10 disciplines with the highest number of articles on Populus euphratica in the Web of Science database.
Figure 3. The 10 disciplines with the highest number of articles on Populus euphratica in the Web of Science database.
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Forests 14 00714 g004 550
Figure 4. Co-occurrence distribution of keywords in the Chinese National Knowledge Infrastructure database. The node size represents the number of references corresponding to the keywords, while the connection between nodes represents the development context and connection between keywords.
Figure 4. Co-occurrence distribution of keywords in the Chinese National Knowledge Infrastructure database. The node size represents the number of references corresponding to the keywords, while the connection between nodes represents the development context and connection between keywords.
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Figure 5. Co-occurrence distribution of keywords in the Web of Science database.
Figure 5. Co-occurrence distribution of keywords in the Web of Science database.
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Figure 6. Clustering distribution of keywords in the Chinese National Knowledge Infrastructure database. Each color block represents a set of all keywords under the cluster, its title name is assigned to synthesize all keywords in the set. The overlapping area located between color blocks represents the degree of correlation between their keyword topics. Few cluster topics do not form color blocks, due to the small number of keywords involved.
Figure 6. Clustering distribution of keywords in the Chinese National Knowledge Infrastructure database. Each color block represents a set of all keywords under the cluster, its title name is assigned to synthesize all keywords in the set. The overlapping area located between color blocks represents the degree of correlation between their keyword topics. Few cluster topics do not form color blocks, due to the small number of keywords involved.
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Figure 7. Clustering distribution of keywords in the Web of Science database.
Figure 7. Clustering distribution of keywords in the Web of Science database.
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Figure 8. Timeline distribution of keywords for different topics in Chinese National Knowledge Infrastructure. The keywords of the same year are concentrated on the same vertical axis, which shows the focus and attention of the research field in the same year. The keywords of the same cluster are concentrated on the same horizontal axis, showing the historical results of the same cluster. Through corresponding the axis, the timeline diagram of Populus euphratica forest research is obtained. Every two nodes and the connection in the diagram represent the inheritance and continuation of the two keywords, and the period between them.
Figure 8. Timeline distribution of keywords for different topics in Chinese National Knowledge Infrastructure. The keywords of the same year are concentrated on the same vertical axis, which shows the focus and attention of the research field in the same year. The keywords of the same cluster are concentrated on the same horizontal axis, showing the historical results of the same cluster. Through corresponding the axis, the timeline diagram of Populus euphratica forest research is obtained. Every two nodes and the connection in the diagram represent the inheritance and continuation of the two keywords, and the period between them.
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Figure 9. Timeline distribution of keywords for different topics in Web of Science.
Figure 9. Timeline distribution of keywords for different topics in Web of Science.
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Figure 10. The time-zone view of hot keywords in the Chinese National Knowledge Infrastructure database. The size of nodes represents the number of references that correspond to keywords. Each node is horizontally distributed in the corresponding year. The connection between nodes reflects the inheritance and continuity of keywords. The type and intensity of connection lines between different years reflect the influence of research results in the whole period.
Figure 10. The time-zone view of hot keywords in the Chinese National Knowledge Infrastructure database. The size of nodes represents the number of references that correspond to keywords. Each node is horizontally distributed in the corresponding year. The connection between nodes reflects the inheritance and continuity of keywords. The type and intensity of connection lines between different years reflect the influence of research results in the whole period.
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Figure 11. The time-zone view of hot keywords in the Web of Science database.
Figure 11. The time-zone view of hot keywords in the Web of Science database.
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Table
Table 1. The top 5 countries in the Web of Science for the number of publications in the literature on Populus euphratica. The centrality value is calculated by the compute node centrality function of CiteSpace software. Centrality refers to the number of times a node acts as the shortest bridge between the other two nodes. Using the structural hole theory of scientific knowledge graph, the greater the betweenness centrality of the node, the greater its influence, and countries with centrality >0.1 indicate that they play an important role as a hub in the network.
Table 1. The top 5 countries in the Web of Science for the number of publications in the literature on Populus euphratica. The centrality value is calculated by the compute node centrality function of CiteSpace software. Centrality refers to the number of times a node acts as the shortest bridge between the other two nodes. Using the structural hole theory of scientific knowledge graph, the greater the betweenness centrality of the node, the greater its influence, and countries with centrality >0.1 indicate that they play an important role as a hub in the network.
NumberCountCentralityStarting YearCountry
15390.582008CHINA
2890.462008GERMANY
3620.062009USA
4210.012009AUSTRALIA
5180.032008IRAN
Table
Table 2. List of top 10 countries with high burst strength from 2007 to 2022. The thickened red segment in the table shows the year of high burst strength in each country; strength represents the outbreak intensity in the year of high bursts strengths for each country. Since the WOS database did not register the literature records related to P. euphratica until 2007, the period for correlation analysis in high burst strength is defined as that of 2007–2022.
Table 2. List of top 10 countries with high burst strength from 2007 to 2022. The thickened red segment in the table shows the year of high burst strength in each country; strength represents the outbreak intensity in the year of high bursts strengths for each country. Since the WOS database did not register the literature records related to P. euphratica until 2007, the period for correlation analysis in high burst strength is defined as that of 2007–2022.
CountriesStrengthBegin—End2007–2022
GERMANY9.062008–2011▂▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂
JAPAN2.082008–2009▂▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂
UZBEKISTAN1.682010–2012▂▂▂▃▃▃▂▂▂▂▂▂▂▂▂▂▂
PAKISTAN1.622010–2011▂▂▂▃▃▂▂▂▂▂▂▂▂▂▂▂▂
lTALY1.922012–2015▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂▂
SCOTLAND1.422012–2013▂▂▂▂▂▃▃▂▂▂▂▂▂▂▂▂▂
IRAN1.522014–2015▂▂▂▂▂▂▂▃▃▂▂▂▂▂▂▂▂
AUSTRALIA2.732016–2019▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂
USA2.612020–2022▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃
FINLAND1.282020–2022▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃
Table
Table 3. List of top 10 keywords with high burst strength in the Chinese National Knowledge Infrastructure database from period of 1992–2022.
Table 3. List of top 10 keywords with high burst strength in the Chinese National Knowledge Infrastructure database from period of 1992–2022.
CountriesStrengthBegin—End1992–2022
Populus euphratica4.891993–1996▂▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂
ecological environment4.841995–2006▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂
Xinjiang6.761998–2010▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂
natural vegetation5.172002–2005▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂
groundwater level8.402003–2009▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂
Tarim River5.902004–2008▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂
lower Heihe River4.422007–2014▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▂▂▂▂▂
P. Pruinosa4.272012–2014▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂
salt stress5.942013–2018▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▂▂
photosynthetic characteristics4.302019–2022▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Table
Table 4. List of top 10 keywords with high burst strength in the Web of Science database, period of 2007–2022.
Table 4. List of top 10 keywords with high burst strength in the Web of Science database, period of 2007–2022.
CountriesStrengthBegin—End2007–2022
transport6.472007–2010▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂
stress4.692007–2012▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂
sodium3.562009–2010▂▂▃▃▂▂▂▂▂▂▂▂▂▂▂▂
Xinjiang4.652013–2015▂▂▂▂▂▂▃▃▃▂▂▂▂▂▂▂
sap flow5.342016–2018▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂
soil water3.612016–2018▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂
climate change5.682018–2022▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃
riparian forest3.562018–2022▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃
groundwater depth3.872019–2022▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Tamarix ramosissima3.872019–2022▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
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Huang, X.; Lv, R.; Zhou, Z.; Fan, M.; Bai, Y.; Ding, Y.; Yang, G. CiteSpace Software Visualization Analyses of the Last Thirty Years of Research on Populus euphratica. Forests 2023, 14, 714. https://doi.org/10.3390/f14040714

AMA Style

Huang X, Lv R, Zhou Z, Fan M, Bai Y, Ding Y, Yang G. CiteSpace Software Visualization Analyses of the Last Thirty Years of Research on Populus euphratica. Forests. 2023; 14(4):714. https://doi.org/10.3390/f14040714

Chicago/Turabian Style

Huang, Xin, Ruiheng Lv, Zhengli Zhou, Min Fan, Yinping Bai, Yihang Ding, and Gang Yang. 2023. "CiteSpace Software Visualization Analyses of the Last Thirty Years of Research on Populus euphratica" Forests 14, no. 4: 714. https://doi.org/10.3390/f14040714

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