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Article

Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China

by
Yan Qin
1,2,
Wenhui Liu
1,
Feng He
2,* and
Xianglin Li
2
1
Key Laboratory of Superior Forage Germplasm in the Qinghai-Tibetan Plateau, Academy of Animal and Veterinary Sciences, Qinghai University, Xining 810016, China
2
Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
*
Author to whom correspondence should be addressed.
Agronomy 2022, 12(10), 2515; https://doi.org/10.3390/agronomy12102515
Submission received: 9 September 2022 / Revised: 11 October 2022 / Accepted: 14 October 2022 / Published: 15 October 2022
(This article belongs to the Special Issue Modeling and Monitoring of Grassland Ecosystem Productivity, Carbon Assimilation and Allocation)
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Abstract

:
Although nitrogen (N) and phosphorus (P) fertilization are important for maintaining the health and productivity of Leymus chinensis steppe, their impact on the abundance and community structure of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in this ecosystem is still unclear. We used the amoA gene as a molecular marker to monitor changes in AOA and AOB under low and high N and P fertilization and applied the resin-core technique to measure soil N mineralization. We found that the abundance of AOA based on amoA gene copies, ranging from 7.51 × 107 to 1.23 × 108 copies g−1 soil, was higher than that of AOB. Fertilization, especially high N and P, increased the number of amoA copies associated with AOB. AOA and AOB communities were dominated by Crenarchaeota and Proteobacteria, respectively. Fertilization decreased the relative abundances of Thaumarchaeota in the AOA community and Proteobacteria in the AOB community and increased the relative abundance of Ammonia_oxidizing_bacteria_ensemble. In N and P fertilization treatments, soil N transformation was closely related to AOB but not AOA. Soil ammonium N and nitrate N reshape the structure of ammonia oxidizers of AOB but not those of AOA on L. chinensis steppes.

1. Introduction

Many recent studies on global warming and groundwater pollution have focused on soil nitrification related to agricultural practices. Nitrification, the biological oxidation of ammonia (NH3) to nitrate (NO3−), is a critical step in the global N cycle. Because N availability is often considered to be a major limiting factor in terrestrial ecosystem productivity, nitrification has been a subject of interest for many decades. Ammonia oxidation is the first, rate-limiting step of nitrification and can be realized by either ammonia-oxidizing bacteria (AOB) or ammonia-oxidizing archaea (AOA), both ubiquitous in agricultural soils [1,2,3]. As evidence has accrued that AOA are more abundant than AOB in currently analyzed soils [4,5], the principles underlying the response of fertilization and the relative importance of AOB and AOA to nitrification have been brought into focus. PCR- and high-throughput sequencing-based assays targeting a partial stretch of the gene encoding the active-site polypeptide of ammonia monooxygenase (amoA) are important tools in the study of soil microbial structure [6,7,8]. The amoA gene has been used as a functional marker for measuring the diversity and abundance of AOA and AOB in various ecological systems and has been applied within different ecosystems to analyze the distribution and relative contribution of AOA and AOB to measured rates of nitrification [9,10,11,12].
Fertilization is commonly used in grassland management to improve ecosystem productivity and health. In grasslands, N cycling is strongly modulated by fertilization [3,13,14,15,16], but soil N mineralization and nitrification in different grasslands have different responses to N deposition. Although fertilization increases net and total soil mineralization rates, its long-term application can reduce the rate of soil N mineralization [17,18]. The N mineralization rate of desertified grassland and alpine meadow is positively correlated with N addition [19,20]. In a typical grassland in Inner Mongolia, however, low N addition has been found to significantly increase soil net N mineralization, whereas high N addition decreases this process [21,22]. In a previous study, we examined the effects of N and P addition on soil net N nitrification. We found that soil nitrification and reactive N availability were strengthened by N addition but reduced by P addition [23]. Consequently, the effect of fertilization on soil N transformation is obviously complex and closely related to soil properties, fertilization mode, vegetation type, and site factors. A fertilizer-based biological mechanistic effect on soil N transformation—N addition in particular—has been observed. Potential nitrification rates and ammonia-oxidizing microorganisms have been found to be affected by N fertilizer application in alpine grassland ecosystems and in a typical temperate steppe [5,24]. In the present study, we analyzed the response of ammonia-oxidizing microorganisms to understand the effects of N and P addition on ecosystem functions. We addressed two questions: (1) do N and P fertilization reshape the AOA and AOB abundance and structure of L. chinensis steppe? (2) How does fertilization reshape the ammonia-oxidizer abundance and structure of L. chinensis steppe?

2. Materials and Methods

2.1. Study Site

The experimental plots used in this study were established on a typical steppe in Saibei County (41°45′57″ N, 115°39′48″ E; 1400 m), Hebei Province, China. Over the past 10 years, the mean annual rainfall at the study site was 403 mm, with a peak in July, and the annual average temperature was 4.2 °C. The soil is a chestnut soil in the Chinese classification system and a Calcic-Orthic Aridisol in the US system, with a bulk density of 1.27 g cm−3, 1.45% organic carbon, 2.12 g kg−1 total N, and 0.63 g kg−1 total phosphorus, and a pH of 6.94. The experimental grassland, whose plant community was dominated by Leymus chinensis, Stipa krylovii, Artemisia frigida, Artemisia eriopoda, and Cleistogenes squarrosa, was cut for hay once a year.

2.2. Experimental Design

The experiment field was established in September 2013 with a random complete block design that included four replications of six treatments: CK (control, without fertilization); LN (urea, 50 kg ha−1 year−1); HN (urea, 150 kg ha−1 year−1); P (calcium superphosphate [CAP], 100 kg ha−1 year−1); LNP (urea, 50 kg ha−1 year−1; CAP, 10 kg ha−1 year−1); and HNP (urea, 150 kg ha−1 year−1; CAP, 100 kg ha−1 year−1). The size of each plot was 20 m2 (4 m × 5 m), with a 1 m wide buffer zone among plots. Fertilizer was applied twice in 2014: half of it was applied in early May and the rest in early July.

2.3. Soil Sampling

The resin-core technique was used to measure N mineralization as follows. First, the vegetation cover was sheared off just above the ground level. Next, two PVC pipes (inner diameter 7.5 cm; length 12 cm) separated by a distance of 20 cm were quickly rammed into the soil, with care taken to minimize the disturbance of the soil structure. This process was repeated five times. The two PVC pipes were withdrawn, and 2 cm of soil was excavated from the bottom of each hole. The following items were inserted in turn into one of the PVC pipes: the other PVC pipe (to retain the original soil mineral N value), a piece of filter paper, a polythene bag filled with 10 g of anion-exchange resin (AER), another filter paper, and a plaster pad (ply 0.7 cm; diameter 7.5 cm) with a hole in the center. Finally, the assembled PVC pipe was installed and maintained in the field for 30 days of cultivation, from 10 July to 9 August (Figure 1). Soil samples collected on 9 August and sealed in polythene bags were insulated, transported to the laboratory, and immediately sieved through a 2-mm screen. One portion of each sample was frozen in liquid N at −80 °C, and the other portion was air-dried for the determination of abiotic soil properties. The NO3−-N in the AERs were measured at the same time. Net soil nitrification was calculated by subtracting initial NO3−-N from final NO3−-N in soil and AER, and net soil mineralization was calculated as (final NO3−-N in soil + NO3−-N in AER + final NH4+-N in soil) − (initial NO3−-N + initial NH4+-N).

2.4. Soil Characteristics

Soil pH was determined at a soil-to-water ratio of 1:2.5, with a pH meter. Electrical conductivity was measured using a conductivity meter, and soil organic matter (SOM) was measured by the K2Cr2O7 oxidation–reduction titration method. Soil nitrate N (NO3−) and ammonium (NH4+) were extracted by 2 mol·L KCl solution, nitrate N was determined by dual-wavelength ultraviolet spectrophotometry, and ammonium (NH4+) was quantified by the indigo colorimetric method. Nitrate N in AER was extracted by 1.5 mol·L H2SO4 solution and determined by dual-wavelength ultraviolet spectrophotometry. Soil samples were digested in concentrated H2SO4, and then soil total N (TN) was measured using an automatic Kjeldahl nitrogen analyzer (UDK 159, VELP Scientifica, Italy), and total phosphorus (TP) using a flow injection autoanalyzer (FIA Star 5000 Analyzer, Foss, Denmark).

2.5. Soil DNA Extraction and High-Throughput Sequencing

Soil DNA was extracted from 0.5-g soil samples using an EZNA soil DNA kit (Omega Bio-tek, Norcross, GA, USA). The integrity of the extracted DNA was checked on a 1% agarose gel. Real-time polymerase chain reaction (PCR) quantification of archaeal and bacterial amoA genes was carried out using primer pairs amoAF/amoAR [25] and amoA1F/amoA2R [26] on an ABI Applied Biosystems 7500 real-time PCR system (Life Technologies, Carlsbad, CA, USA). qPCR amplifications were performed in 25-μL reaction volumes consisting of 12.5 μL ABI Power SybrGreen qPCR Master Mix (2×), 0.5 μL each of forward and reverse primers (10 μM), 9.5 μL water, and 2 μL template cDNA. Two-step amplification was carried out according to the following protocol: a 10-min template denaturation step at 95 °C, followed by 40 cycles of 95 °C for 15 s and 60 °C for 1 min—when the fluorescence signals were acquired. All samples were amplified in triplicate as technical replicates, and specific amplification was confirmed by the observation of single peaks on dissociation curves. Pyrosequencing of amoA genes for ammonia-oxidizers were amplified for sequencing with the Roche 454 GS FLX+ Titanium platform (Roche 454 Life Sciences, Branford, CT, USA) by Shanghai Majorbio Bio-pharm Technology Co. (Shanghai, China) according to standard protocols.

2.6. Statistical Analysis

Valid sequences were generated from 18 soil samples (i.e., six treatments from blocks 1 to 3, but none from block 4). A total of 218,304 valid sequences were obtained from 261,582 AOA sequences, with an average of 12,128 sequences per sample. Out of 308,374 AOB sequences, 250,296 were valid, with an average of 13,905 sequences per sample. The resulting sequences were processed using QIIME v1.17. After the removal of sequences having an average quality score < 20 over a 50-bp sliding window, sequences shorter than 200 bp, sequences with homopolymers longer than six nucleotides, those containing ambiguous base calls, and incorrect primer sequences, the remaining high-quality AOA and AOB sequences had average lengths of 422.31 and 453.94 bp, respectively. Operational taxonomic units were clustered using a 97% similarity cutoff in UPARSE v7.1 (http://drive5.com/uparse/ (accessed on 23 December 2014), and chimeric sequences were identified and removed using UCHIME. The taxonomy of each 16S rRNA gene sequence was analyzed with RDP Classifier (http://rdp.cme.msu.edu/ (accessed on 12 January 2015) against the SILVA (SSU115) 16S rRNA database using a confidence threshold of 70%.
ANOVA as implemented in SPSS v19 was used to examine the effects of N and P fertilization on the relative abundance of AOA and AOB based on amoA gene copies, and correlation bivariate models were applied to obtain Pearson relationship coefficients among AOA, AOB, and soil characteristics. Significant differences were evaluated using Student’s t-test. The results of statistical analyses were visualized graphically using Microsoft Excel 2010 (Microsoft, Seattle, WA, USA).

3. Results and Analysis

3.1. Effect of N and P Fertilization on the Abundance of AOA and AOB

The abundance of AOA and AOB was estimated by quantifying the amoA gene. AOA amoA gene copy numbers ranged from 7.51 × 107 to 1.23 × 108 g−1 dry soil (Figure 2A, Table S1). Among the six treatments, HNP always had the highest AOA amoA gene copy numbers, which were significantly higher than those in LN and LNP treatments (p < 0.05); in particular, copy numbers in HNP were 1.64-fold higher compared with the lowest values, which were recorded in LNP. Fertilization had no effect on soil AOA amoA gene copy numbers (p > 0.05). AOB amoA gene copy numbers ranged from 7.90 × 103 to 1.05 × 105 g−1 dry soil (Figure 2B). Fertilization increased AOB amoA gene copy numbers, which were significantly higher in HNP (1.05 × 105 g−1 dry soil) than in other treatments (p < 0.05). AOB amoA gene copy numbers were not significantly different among LN, LNP, HN, and P treatments (p > 0.05). The ratio of AOA to AOB amoA gene copies, which ranged from 1.17 × 103 to 1.36 × 104 across treatments (Figure 2C), was decreased by fertilization.

3.2. Effect of N and P Fertilization on AOA and AOB Community Structures

At the phylum level, 78.24% of AOA amoA sequences were affiliated with Crenarchaeota. In addition, Thaumarchaeota and “Environmental_samples” were associated with 18.07% and 3.69% of sequences, whereas “Archaea_unclassified” accounted for less than 0.01%. The average relative abundance of Crenarchaeota in the six treatments was 78.65% (Figure 3A, Table S1), with no significant differences among treatments (p > 0.05). The relative abundance of “Environmental_samples”, the second largest phylum category in this study, ranged from 14.88% to 20.45%, with no significant differences observed among treatments. Fertilization decreased the relative abundance of Thaumarchaeota by 19.12%, 68.38%, 29.45%, 40.81%, and 35.48%, respectively, in LN, LNP, HN, HNP, and P relative to CK, but only the decrease in LNP was significant (p < 0.05).
The dominant phylum associated with AOB amoA sequences was Proteobacteria, which accounted for 93.00% of total sequences. The next most abundant phyla corresponded to the categories of “Environmental_samples” and “Ammonia_oxidizing_bacteria_ensemble”, corresponding to 5.21% and 0.83% of sequences, respectively. Five other phyla (“Others”), namely, “Bacteria_unclassified”, Actinobacteria, “unclassified”, “candidate_division_NC10”, and Crenarchaeota, collectively accounted for less than 1%. The relative abundance of Proteobacteria in the six fertilization treatments ranged from 89.86% (HN) to 96.30% (P) (Figure 3B); among fertilization treatments, this value exhibited a downward trend upon addition of N (LN, LNP, HN, and HNP) and was significantly different, except in LN, from that of CK (P < 0.05). The relative abundance of “Environmental_samples” ranged from 1.98% (P) to 8.42% (HN) in the different treatments; similar to Proteobacteria, values were 1.98-, 3.37-, 4.01-, and 3.59-fold lower in LN, LNP, HN, and HNP compared with CK, and, except for LK, these differences were significant (p < 0.05). The relative abundance of “Ammonia_oxidizing_bacteria_ensemble” decreased following N and P addition but increased in the LNP treatment; however, no significant differences were detected relative to CK. Finally, the relative abundance of AOB classified as “Others” ranged from 0.01% (P) to 1.93% (HN) in the different treatments. Because of the large standard errors, no statistically significant differences among treatments were discernable.

3.3. Relationship between the Abundance of Ammonia Oxidizers and Soil Characteristics

The correlation coefficient of the relationship between the abundance of archaea amoA genes and ammonium N was 0.54 (p < 0.05). The coefficients of the correlation between the abundance of bacterial amoA genes and net soil nitrification, total N, total phosphorus, and ammonium N were 0.56, 0.69, 0.71, and 0.51 (p < 0.05), respectively (Table 1; Figure 4).

3.4. Relationship between AOA and AOB Community Structures and Soil Characteristics

The proportion of amoA gene copies belonging to Proteobacteria among detected phyla was significantly correlated with soil ammonium N and nitrate N, with correlation coefficients of −0.53 and −0.56, respectively. The proportion assigned to “ammonia-oxidizing_bacteria_ensemble” was significantly correlated with net soil N mineralization, soil ammonium N, and nitrate N, with correlation coefficients of 0.48, 0.51, and 0.65, respectively (Table 2; Figure 5).

4. Discussion

In this study, soil AOA and AOB amoA abundance, reflecting the relative abundance of AOB and AOA in DNA extracts, was measured by real-time PCR. Regardless of whether or not N or P fertilizers were applied, AOA amoA was far more abundant than AOB amoA in soil samples collected from the L. chinensis steppe in northern China. Shen et al. (2011) also found that the abundance of AOB was markedly lower than that of AOA in a low-fertility, semiarid temperate grassland located approximately 200 km away from our study region [27]. These results are consistent with those obtained from studies of other ecosystems [28,29]. Several studies have shown that high N addition stimulates the growth of AOB but not AOA, and their authors have concluded that AOB are a potential sensitive indicator for assessing the effect of N addition [30,31,32]. Similarly, AOA abundance is insensitive to the addition of chemical fertilizer, especially phosphorus, and follows a similar trend to that of soil net N nitrification and net N mineralization [23]. These results suggest that AOB are responsible for the active soil nitrification observed in our study. Biological N transformation processes in soil, which are mainly driven by microorganisms, are affected by the addition of mineral fertilizers and depend on fertilization rate, soil properties, and vegetation forms [3,33,34,35]. The significant relationship between bacterial amoA and net soil N mineralization observed in our study suggests that AOB are more sensitive than AOA to N fertilizer application (Table 1) and that AOB abundance is closely related to N transformation.
Environmental parameters, such as temperature, pH, and nutrient levels, vary among soil systems and have a great impact on the community, abundance, and activity of AOB and AOA in soil. Both AOA and AOB typically play roles in habitats with high ammonia N contents (Table 1). As the energy source for ammonia oxidizers, NH4+ availability is likely to impact AOB and AOA populations following the addition of external N fertilizer. The AOA community is affected by pH, whereas the AOB community is mainly shaped by the SOC and N fertilization rate. Hou et al. (2013) found that the bacterial phylum Aquificae and the archaeal phylum Crenarchaeota were dominant in hot springs in Tengchong, China [36]. In another study, five bacterial phyla were dominant: Proteobacteria, Firmicutes, Nitrospirae, Thermotogae, and Cyanobacteria, with the greatest diversity observed in Proteobacteria [37]. In the present study, AOA and AOB communities were dominated by Crenarchaeota and Proteobacteria, respectively. The higher number of detected archaeal amoA copies may be due to the fact that AOA are more susceptible to lysis than AOB. The significant relationship of AOA with indexes such as soil N transformation indicates that AOB were more sensitive to N and P fertilizer application in this study.

5. Conclusions

In this study, quantitative PCR and high-throughput sequencing were used to monitor AOB and AOA abundance and community structure under N and P fertilization on a steppe managed for haymaking in northern China. AOB abundance especially increased following high N and P fertilizer application. At the phylum level, AOA and AOB communities were dominated by Crenarchaeota and Proteobacteria, respectively. The AOA community structure was not sensitive to changes in soil properties, whereas that of AOB was significantly correlated with net soil nitrification and ammonium N and nitrate N contents. Soil N transformation was closely related to the abundance of Proteobacteria and “ammonia-oxidizing_bacteria_ensemble”, both included in the AOB community in this study.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy12102515/s1, Table S1: Abundance and structure of ammonia-oxidizing archaea and ammonia-oxidizing bacteria.

Author Contributions

Conceptualization, Y.Q. and F.H.; methodology, Y.Q.; investigation, Y.Q.; data curation, Y.Q.; writing—original draft preparation, Y.Q. and F.H.; writing—review and editing, Y.Q., F.H., W.L. and X.L.; and funding acquisition, Y.Q., F.H. and X.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Qinghai innovation platform construction project (2022-ZJ-Y01), the Agricultural Science and Technology Innovation Program (ASTIP-IAS14), and the earmarked fund for CARS (CARS-34).

Data Availability Statement

All data supporting the findings of this study are included in the article.

Acknowledgments

We thank to Guoling Quan, Shuyi Bi, Dong Wang, and Kaiyun Xie for their assistance with field data collection. We also thank the anonymous reviewers and editors for their comments to improve our manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Experiment field layout and anion-exchange resin-core technique.
Figure 1. Experiment field layout and anion-exchange resin-core technique.
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Figure 2. Effect of N and P addition on the abundance of archaeal amoA gene (A), bacterial amoA gene (B), and AOA/AOB (C) in soil. Error bars denote SE. Bars with different lowercase letters are significantly different (p < 0.05). CK, no fertilizer; LN, low-dose N fertilizer; LNP, low-dose N and P fertilizers; HN, high-dose N fertilizer; HNP, high-dose N and P fertilizers; P, high-dose P fertilizer. AOA, ammonia-oxidizing archaea; and AOB, ammonia-oxidizing bacteria.
Figure 2. Effect of N and P addition on the abundance of archaeal amoA gene (A), bacterial amoA gene (B), and AOA/AOB (C) in soil. Error bars denote SE. Bars with different lowercase letters are significantly different (p < 0.05). CK, no fertilizer; LN, low-dose N fertilizer; LNP, low-dose N and P fertilizers; HN, high-dose N fertilizer; HNP, high-dose N and P fertilizers; P, high-dose P fertilizer. AOA, ammonia-oxidizing archaea; and AOB, ammonia-oxidizing bacteria.
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Figure 3. Effect of N and P addition on the relative abundance of AOA (A) and AOB (B) communities. Different lowercase letters indicate significant differences at p < 0.05. AOA, ammonia-oxidizing archaea; AOB, ammonia-oxidizing bacteria; CK, no fertilizer; LN, low-dose N fertilizer; LNP, low-dose N and P fertilizers; HN, high-dose N fertilizer; HNP, high-dose N and P fertilizers; and P, high-dose P fertilizer.
Figure 3. Effect of N and P addition on the relative abundance of AOA (A) and AOB (B) communities. Different lowercase letters indicate significant differences at p < 0.05. AOA, ammonia-oxidizing archaea; AOB, ammonia-oxidizing bacteria; CK, no fertilizer; LN, low-dose N fertilizer; LNP, low-dose N and P fertilizers; HN, high-dose N fertilizer; HNP, high-dose N and P fertilizers; and P, high-dose P fertilizer.
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Figure 4. Correlation analysis of archaeal and bacterial amoA gene abundance and soil characteristics. (A–E) Correlations between archaeal amoA gene abundance and ammonium nitrogen (A), bacterial amoA gene abundances and net soil nitrification (B), total nitrogen (C), total phosphorus (D), and ammonium nitrogen (E).
Figure 4. Correlation analysis of archaeal and bacterial amoA gene abundance and soil characteristics. (A–E) Correlations between archaeal amoA gene abundance and ammonium nitrogen (A), bacterial amoA gene abundances and net soil nitrification (B), total nitrogen (C), total phosphorus (D), and ammonium nitrogen (E).
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Figure 5. Correlation analysis of AOA and AOB community structures and soil characteristics. (A,B) Correlation between the relative proportion of Proteobacteria and (A) ammonium nitrogen and (B) nitrate nitrogen. (C–E) Correlation between the relative proportion of “ammonia-oxidizing_bacteria_ensemble” and (C) net soil nitrogen mineralization, (D) soil ammonium nitrogen, and (E) nitrate nitrogen.
Figure 5. Correlation analysis of AOA and AOB community structures and soil characteristics. (A,B) Correlation between the relative proportion of Proteobacteria and (A) ammonium nitrogen and (B) nitrate nitrogen. (C–E) Correlation between the relative proportion of “ammonia-oxidizing_bacteria_ensemble” and (C) net soil nitrogen mineralization, (D) soil ammonium nitrogen, and (E) nitrate nitrogen.
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Table
Table 1. Correlation analysis of archaeal and bacterial amoA gene abundances and soil characteristics.
Table 1. Correlation analysis of archaeal and bacterial amoA gene abundances and soil characteristics.
NSNNSMpHECTNTPSOMANNNC/N
Abundance of archaea amoA gene0.240.31−0.210.120.400.210.150.54 *0.37−0.09
Abundance of bacterial amoA gene0.200.56 *0.010.000.69 *0.71 *−0.130.51 *0.37−0.39
Note: *, significant (p < 0.05); ns, not significant. NSN, net soil nitrification; NSM, net soil nitrogen mineralization; EC, electrical conductivity; TN, total nitrogen; TP, total phosphorus; SOM, soil organic matter; AN, ammonium nitrogen; NN, nitrate nitrogen; and C/N, carbon-to-nitrogen ratio.
Table
Table 2. Correlation analysis of AOA and AOB community structures and soil characteristics.
Table 2. Correlation analysis of AOA and AOB community structures and soil characteristics.
DomainPhylaNSNNSMpHECTNTPSOMANNNC/N
AOACrenarchaeota0.290.09−0.410.180.16−0.210.150.040.26−0.04
Environmental_samples −0.31−0.050.40−0.18−0.020.29−0.17−0.08−0.24−0.09
Thaumarchaeota0.01−0.090.08−0.03−0.33−0.150.030.08−0.060.29
Archaea_unclassified−0.14−0.410.46−0.28−0.09−0.17−0.08−0.350.10−0.07
AOBProteobacteria−0.41−0.270.180.16−0.33−0.24−0.16−0.53 *−0.56 *0.12
Environmental_samples −0.13−0.040.12−0.240.120.08−0.26−0.38−0.25−0.25
ammonia-oxidizing_bacteria_ensemble0.48 *0.34−0.27−0.170.240.280.050.51 *0.65 *−0.12
others −0.10−0.180.170.170.11−0.160.420.25−0.120.17
Note: *, significant (p < 0.05); ns, not significant. AOA, ammonia-oxidizing archaea; AOB, ammonia-oxidizing bacteria; NSN, net soil nitrification; NSM, net soil nitrogen mineralization; EC, electrical conductivity; TN, total nitrogen; TP, total phosphorus; SOM, soil organic matter; AN, ammonium nitrogen; NN, nitrate nitrogen; and C/N, carbon-to-nitrogen ratio.
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Qin, Y.; Liu, W.; He, F.; Li, X. Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China. Agronomy 2022, 12, 2515. https://doi.org/10.3390/agronomy12102515

AMA Style

Qin Y, Liu W, He F, Li X. Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China. Agronomy. 2022; 12(10):2515. https://doi.org/10.3390/agronomy12102515

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Qin, Yan, Wenhui Liu, Feng He, and Xianglin Li. 2022. "Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China" Agronomy 12, no. 10: 2515. https://doi.org/10.3390/agronomy12102515

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