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Article

Effect of Brassinolide on Stoichiometric Stability Characteristics of Tall Fescue under Drought Stress in Ecological Restoration

by
Roujia Kang
1,
Mingyi Li
2,*,
Shiwei Guo
2,
Dong Xia
3,
Liming Liu
2,
Wenhao Dong
4,
Wennian Xu
2 and
Yucai Lv
1
1
College of Biological & Pharmaceutical Sciences, China Three Gorges University, Yichang 443002, China
2
Key Laboratory of Geological Hazards on Three Gorges Reservoir Area, Ministry of Education, China Three Gorges University, Yichang 443002, China
3
College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang 443002, China
4
Hubei Runzhi Ecological Technology Co., Ltd., Yichang 443002, China
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(14), 5942; https://doi.org/10.3390/su16145942
Submission received: 21 May 2024 / Revised: 27 June 2024 / Accepted: 5 July 2024 / Published: 12 July 2024
Browse Figures
Versions Notes

Abstract

:
In order to investigate the effects of brassinolide (BR) on the ecological stoichiometric characteristics and internal stability of plants in slope ecological protection under different drought conditions, the biomass, proline content, nutrient content, and internal stability of tall fescue (Festuca arundinacea) in three stress periods were analyzed by weighing water control method, with three drought degrees (75% ± 5%), mild drought (55% ± 5%) and severe drought (35% ± 5%) and four BR concentrations (0 mg/L, 0.05 mg/L, 0.2 mg/L and 0.5 mg/L). The results showed that drought stress resulted in a decrease in plant biomass and nutrient content, and there were differences in carbon, nitrogen and phosphorus contents and their stoichiometric ratios in different organs. Spraying suitable concentration of BR could alleviate plant nutrient loss and promote nutrient accumulation of the tall fescue. Under normal water spraying conditions 0.2 mg/L, under mild and severe drought conditions with spraying of 0.5 mg/L BR, it is most suitable for the nutrient accumulation in tall fescue. The tall fescue showed high sensitivity to exogenous BR input, and the internal stability of the underground part of the tall fescue increased clearly. BR is propitious to the synthesis of proline and enhances the drought resistance of plants. According to stoichiometric characteristics, BR can improve the nitrogen and phosphorus utilization efficiency of tall fescue to a certain extent, and the results of the nitrogen and phosphorus ratio show that nitrogen is the main factor limiting plant growth in a vegetation concrete ecological restoration system, which can supplement nitrogen to accelerate the process of vegetation restoration. The application of BR can improve the biomass and stress resistance of tall fescue, adjust the nutrient distribution strategy and stoichiometric stability, and alleviate the adverse effects of drought on plants. This study provides new ideas and methods for ecological restoration and vegetation reconstruction in arid areas.

1. Introduction

Hydropower, transportation, mining, and other engineering construction inevitably impact the ecological environment. The ecological system is seriously disturbed, particularly by the slope wound formed by earth and stone excavation. The loss of habitat conditions leads to soil erosion, ecological destruction, and landscape imbalance. Therefore, slope treatment has received increasing attention [1,2]. Vegetation concrete technology provides the dual functions of engineering protection and ecological greenery, making it an effective means of implementing ecological restoration. The vegetation concrete substrate adheres to the rock surface with a strong cohesive force through the joint action of barbed wire, anchor nails, and cement arranged on the rock surface. This creates a growth environment for vegetation and promotes the formation and succession of a vegetation community [3,4]. However, during the early stages of vegetation restoration, slope protection plants may experience drought stress due to insufficient water infiltration and evapotranspiration caused by high and steep slopes. This problem is further exacerbated by the drought environment caused by global climate change [5,6], which can significantly impact the normal growth and development of plants [7]. Long-term drought can cause plant wilting and death, which can limit the restoration process and sustainability of ecological communities in engineering disturbance areas.
In an arid environment, control methods such as setting up permanent irrigation systems [8] and replanting vegetation are often used in the process of slope ecological restoration to alleviate drought stress. However, this approach does not have a long-term positive impact on plant nutrient utilization or ecosystem self-maintenance. As a result, it cannot meet the increasing demands of ecological environment protection and sustainable development [9]. Improving the stress resistance and nutrient utilization efficiency of ecological restoration plants and promoting the coupling balance and sustainable restoration of nutrients in ecosystems are urgent scientific problems [10]. BR is a natural plant hormone that works in conjunction with other plant hormones to facilitate plant growth and development [11]. The regulation of various physiological functions of plants can improve their stress resistance. This includes promoting cell division and elongation [12], regulating flower bud differentiation and the flowering process [13], regulating chloroplast structure and function [14], promoting the accumulation of plant photosynthetic products, enhancing antioxidant enzyme activity, regulating osmotic substance accumulation, and reducing peroxide accumulation [15]. Numerous studies have demonstrated that an optimal concentration of BR can improve plants’ resistance to abiotic stresses, including drought [16], salt [16], heavy metal [17], and temperature [18] stress. Additionally, BR plays a crucial regulatory role in plant growth and development. Currently, it has been extensively used in agricultural production research [19]. However, no research has been reported on its application in the field of slope ecological restoration. Therefore, if it can be used as a regulator to alleviate the limited application of vegetation concrete ecological slope protection technology in arid areas, it will contribute to the health and sustainability of ecological protection projects.
The key to the successful restoration of a disturbed slope ecosystem is to construct habitats on the slope with poor site conditions and promote the stable succession of plant communities. Plant growth is primarily driven by the accumulation of basic structural and functional substances such as carbon, nitrogen, and phosphorus, and the adjustment of their relative proportions [20,21]. This process is closely linked to the interaction between plants and their environment, which can be analyzed using ecological chemometrics. The theory of homeostasis is the main theory of ecological chemometrics. It explains that organisms can maintain the stability of their element composition within a narrow range, even in a changing environment [22,23]. This ability is helpful in understanding the nutrient turnover process and nutrient restriction mechanism of ecosystems, and plays an active role in maintaining the stability of the ecological protection system of disturbed slopes. Currently, the majority of related studies concentrate on grassland, forest, and wetland ecosystems [24,25,26]. However, there is a lack of research on the stoichiometric characteristics of herbaceous plants in slope protection ecosystems and their ability to adapt to arid environments by adjusting their stoichiometric internal stability [27]. Relevant scholars [28,29] confirmed that the internal stability is affected by plant organs and environmental factors, and the difference between influencing factors makes the ecological stoichiometric internal stability of different plants respond differently to the environment.
Therefore, this study aims to clarify the impact of BR application on slope ecological restoration and its effect on the resistance of slope protection plants to drought stress. The research focuses on the vegetation concrete ecological protection technology and uses tall fescue as the research object. The study investigates the impact of drought stress on the nutrient allocation and metabolism characteristics of slope protection plants. The article discusses the stoichiometry differences between various organs and their internal stability, as well as the nutrient utilization and ecological adaptation strategies of slope protection plants under different BR application concentrations. The aim is to provide new ideas and theoretical support for ecological restoration and vegetation reconstruction in arid areas.

2. Materials and Methods

2.1. Materials

The test materials consisted of planting soil, cement, habitat base substrate improvers, organic materials, and tall fescue. The planting soil was selected from the local yellow-brown loam soil of Yichang City, Hubei Province. It was air-dried, had impurities removed, and was crushed through a 2 mm sieve for later use. The cement used was P·O42.5 ordinary Portland cement produced by Yichang Huaxin Cement Factory Habitat (Yichang, China). The habitat substrate improver utilizes the Runzhi ecological agent produced by Hubei Runzhi Ecological Technology Co., LTD (Yichang, China). The organic material selected was sawdust provided by Huaxin Timber Mill on Yemingzhu Road in Yichang City, Hubei Province. The vegetated concrete slope protection project provided tall fescue seeds. The configuration scheme adheres to the current national energy industry standard “Technical Code for Ecological Restoration of Vegetation Concrete on Steep Slope of Hydropower Projects” (NB/T 35082-2016), The mass ratio of each dry material used in preparing the concrete is as follows: planting soil:cement:organic material:improver = 100:8:6:4.

2.2. Experimental Design

This study was conducted from February 2023 to July 2023. The entire experiment was carried out in the greenhouse of the Cement-based Ecological Restoration Experimental Base at China Three Gorges University, without any natural precipitation, and the temperature was maintained at 15–25 °C. The commonly used slope angle for ecological restoration of slopes with planted concrete in potted plants was 60°. The air humidity varied under three different water conditions: well water (WW) conditions had an air humidity of approximately 50% relative humidity; light drought (LD) conditions had an air humidity of approximately 30% relative humidity; and severe drought (SD) conditions had an air humidity of approximately 20% relative humidity. A pot control experiment was employed, where vegetation concrete was prepared and loaded into pots. Each pot was divided into two layers: an 8 cm base layer without seeds and a 2 cm surface layer with seeds. After sowing, the plants were watered and cared for daily, and drought stress was induced after 14 days. The water content was controlled using a weighing method to simulate varying degrees of drought. Weighing was conducted every two days to maintain three water gradients: WW, LD, and SD. Concurrently, four different concentrations of BR were sprayed on the leaves and stems: CK (0 mg/L), series 1 (0.05 mg/L), series 2 (0.2 mg/L), and series 3 (0.5 mg/L). Water was used as a CK until the surfaces of the leaves and stems were fully wet, but no droplets condensed and fell. The spraying was conducted at the beginning of the drought stress, once a day for three consecutive days. The experiment consisted of 12 treatments, with nine repetitions for each treatment, totaling 108 pots. Each pot contained 2.3 kg of vegetation concrete. The stress time was calculated starting from the day after the drought stress treatment. The biomass, proline content, and carbon, nitrogen, and phosphorus content of both the plant and substrate were measured at 30, 60, and 90 days after the stress was induced.

2.3. Test Methods

The tall fescues were harvested after 30, 60, and 90 days of drought. The aboveground and underground parts were separated, impurities were removed and washed, surface moisture was absorbed with absorbent paper, and the green was deoxidized at 105 °C for 30 min. The samples were then dried at 75 °C to a constant weight and crushed for further use. The substrate samples were mixed thoroughly and taken to the laboratory for air drying. Impurities, such as roots, were removed after passing through a 1 mm sieve for future use. Organic carbon was measured using the potassium dichromate volume-external heating method [30]. Total nitrogen was digested using H2SO4-H2O2 and determined by a flow analyzer (Breda, Netherlands). Total phosphorus was determined using the molybdenum-antimony resistance colorimetric method [31]. The content of proline was determined using acid ninhydrin colorimetry [32].

2.4. Data Analysis

Sterner and Elser’s internal stability models [33] were used to calculate the internal stability of the plants. The corresponding formula is given as follows:
Y = C X 1 / H
The formula for the index of the model is as follows: Y represents the content and ratio of carbon, nitrogen, and phosphorus in different parts of the plant, while X represents the content and ratio of carbon, nitrogen, and phosphorus elements in the substrate. C is the fitting constant, and H is the internal stability index. The formula 0 < 1/H < 0.25 indicates the steady-state, 0.25 < 1/H < 0.50 indicates the weakly steady-state, 0.50 < 1/H < 0.75 indicates weakly sensitive, and 1/H > 0.75 indicates sensitive. When 1/H is negative, the internal stability of plants is discussed with absolute value [34].
The data were processed using Excel 2019 and SPSS 26.0. Excel 2019 was used to calculate the mean value and standard deviation, while SPSS 26.0 was used to conduct three-factor ANOVA and difference analysis for each indicator of the tall fescue under different processing conditions. The internal stability index of each part of the tall fescue was fitted using the power function, and OriginPro 2022 SR1 software was used for drawing.

3. Results

3.1. Effect of BR on Biomass of Tall Fescue under Drought Stress

Due to worsening drought conditions, the overall biomass of both the aboveground and underground parts of the tall fescue decreased. In normal water conditions, the biomass of the tall fescue initially increased and then decreased with an increase in BR concentration. Overall, the aboveground and underground biomass of the series 2 group increased significantly more than that of the CK group (p < 0.05). The increase was 6.38–12.23% and 1.34–15.50%, respectively. Under mild drought stress, the aboveground and underground biomass of the tall fescue sprayed with BR increased to varying degrees compared to CK. However, there was only a significant difference at 90 days of stress (p < 0.05). Under severe drought stress, various concentrations of BR treatments enhanced the aboveground biomass accumulation of the tall fescue (Table 1). The results of the variance analysis indicate that drought time, drought degree, and BR had a significant impact on the aboveground and underground biomass of tall fescue, with the drought degree having the greatest influence (Table 2).

3.2. Effect of BR on Proline of Tall Fescue under Drought Stress

The proline content of the tall fescue increased with the aggravation of drought stress. In normal water conditions, the proline content of the tall fescue in the BR treatment was higher than that in the CK group. Under mild drought stress, the proline content of the series 2 group increased by 21.60%, 18.42%, and 10.33% compared to the CK group, respectively, but only achieved a significant effect at 60 and 90 days. Under severe drought stress, the series1-series3 groups showed a greater effect compared to the CK group. At 90 days, each group had a significant increase of 6.07–21.69% compared to the CK group (p < 0.05) (Figure 1). The results of the variance analysis showed that drought time had the greatest influence on the proline content of the tall fescue, while the interaction between the drought time and BR concentration had the least influence on the proline content of the tall fescue (Table 2).

3.3. Effect of BR on Carbon Content of Tall Fescue under Drought Stress

The carbon content of the tall fescue, both above ground and underground, decreased with the increasing drought stress (p < 0.05). When sprayed with BR under different drought stress, the aboveground and underground carbon content of the tall fescue showed a different trend compared to the control (CK). Under normal watering conditions, the carbon content of the tall fescue increased by 0.25–29.37% compared to CK. However, the tall fescue had a lower aboveground carbon content than CK when BR was sprayed after 90 days of drought stress. Under mild drought stress, except for 30 days of drought, low concentrations promoted the aboveground and underground carbon content of the tall fescue, while high concentrations inhibited it, especially when the drought lasted for 60 days. Under severe drought stress, the tall fescue exhibited a significant increase in both aboveground and underground carbon content. Spraying BR increased the carbon content of the aboveground and underground parts by 2.54–45.74% and 0.16–31.29%, respectively, compared to CK (Figure 2). The results of the variance analysis indicated that the time and degree of the drought had a significant impact on the carbon content of aboveground and underground parts of the tall fescue (Table 2).

3.4. Effect of BR on Nitrogen Content of Tall Fescue under Drought Stress

The nitrogen content in the aboveground and underground parts of the tall fescue showed a downward trend as the drought degree worsened and was prolonged. When the BR concentration increased under normal water conditions, the nitrogen content of the tall fescue initially increased and then decreased. The nitrogen content of plants in the series 2 treatment increased significantly more than that in the CK group (p < 0.05), by 39.66%; Under mild drought stress, the nitrogen content of the tall fescue treated with BR increased over time. After 30 days of drought, the nitrogen content of underground parts in series 1 and series 3 groups decreased by 14.30% and 7.15%, respectively, compared to the CK group. Under severe drought stress, the nitrogen content in underground parts increased only with the increase in BR concentration after 30 and 90 days of drought (Figure 3). Table 2 shows that the nitrogen content in the aboveground and underground parts of the tall fescue was greatly influenced by the single factors of drought time and drought degree, according to the variance analysis results.

3.5. Effect of BR on Nitrogen Content of Tall Fescue under Drought Stress

The study found that the phosphorus content in the aboveground and underground parts of the tall fescue exhibited different trends under different treatments. Specifically, the aboveground phosphorus content decreased significantly with the aggravation of the drought stress (p < 0.05). Under normal water conditions, spraying BR did not have a significant effect on the phosphorus content in the aboveground part of the tall fescue (p > 0.05). However, the phosphorus content in the underground part showed an overall upward trend with the increasing BR concentration, increasing by 10.33% to 75%. Under mild drought stress, the phosphorus content of all groups, except for the upper part of 30 days of drought and the underground part of 60 days of drought when the BR concentration was series 2, was significantly increased by 50.00% compared to the CK group; Under severe drought stress, the phosphorus content in aboveground parts showed an upward trend under the BR treatment and reached a significant effect at 60 and 90 days. The phosphorus content in underground parts decreased initially with the increase in BR concentration, but then increased. Only after 90 days, the series 3 group showed a significant increase compared to the CK group (Figure 4). The variance analysis results indicate that a single factor significantly affects the phosphorus content in the aerial parts of the tall fescue. Additionally, the results show that drought time has the greatest impact on the phosphorus content in the underground parts of the tall fescue (Table 2).

3.6. Effect of BR on Nitrogen Content of Tall Fescue under Drought Stress

Under the increased stress, the C/N in the aboveground part of the tall fescue decreased, while the C/N in the underground part increased. When sprayed with BR at 90 days under normal water conditions, the tall fescue’s C/N was significantly reduced; Under mild drought stress, the application of BR resulted in a decrease in the C/N of the tall fescue, indicating a higher nitrogen content in the tissue and increased ease of decomposition. Under severe drought stress, the BR treatment significantly increased the carbon and nitrogen content of the tall fescue. The aboveground series 3 group had the best effect, while the underground series 1 group had a better effect (Figure 5). Furthermore, the C/N of the tall fescue is significantly affected by the drought duration, severity, BR concentration, and their interactions (Table 2).
The study found that drought stress significantly affected the C/P of the tall fescue (p < 0.05). Additionally, the C/P of the underground part of the tall fescue showed a consistent downward trend with increasing drought severity. Under normal watering conditions, the C/P in the aboveground parts increased by 7.24 to 24.44% compared to the control group at 60 days after spraying BR. However, series1-series3 decreased by 29.16%, 13.74%, and 30.70%, respectively, compared to the control group at 90 days. Under mild drought stress, the C/P in the underground parts of the tall fescue in series 3 groups was significantly higher than that in the control group (CK), with a maximum increase of 57.13%. Under severe drought stress, except for the aboveground parts at 60 and 90 days, the C/P of the tall fescue generally increased under BR treatment. The underground parts of series 2 group showed the highest increase at 30 days, reaching 156.80% (Figure 6). According to the F value, the drought time, drought degree, BR concentration, and their interactive effects have significant effects on C/P of the tall fescue (p < 0.001, Table 2).
The N/P in the aboveground parts of the tall fescue were significantly different (p < 0.05). Meanwhile, the N/P in the underground parts of the tall fescue showed a significant downward trend with the aggravation of the drought stress. Under normal water conditions, the N/P in the aboveground part increased initially and then decreased with the increase in BR concentration at 60 and 90 days. In the series 2 group, the N/P in the aboveground part increased significantly by 20.25% and 38.65%, respectively, compared to the CK. As a whole, the ratio of nitrogen to phosphorus in the underground part decreased with an increase in BR concentration. Specifically, it decreased by 16.80% to 61.42% and 9.42% to 19.16% at 60 and 90 days, respectively. Under mild drought stress, the N/P in both the aboveground and underground parts of the tall fescue treated with BR increased compared to the control group. The greatest increase was observed in the series 3 group, except for the aboveground parts of the tall fescue under stress for 30 days, with an increase of 110.81%. Under the severe drought stress, the N/P in the aboveground part of the tall fescue decreased with the increasing BR concentration, while the ratio in the underground part increased (Figure 7). Furthermore, variance analysis showed that the BR concentration did not have a significant effect on the nitrogen to phosphorus ratio of aboveground parts (p > 0.05, Table 2).

3.7. Effect of BR on Internal Stability Characteristics of Tall Fescue under Drought Stress

The internal stability model was used to calculate the internal stability indexes of C, N, P and their ratios in the aboveground and underground parts of the tall fescue. The results indicate that the tall fescue’s nitrogen and C/N are sensitive to drought stress. Under drought stress conditions, the indexes of the underground parts showed greater stability than those of the aboveground parts as the degree and duration of the drought stress increased in different treatment groups. Tall fescue distributes nutrients to its underground parts to maintain their stability, and exogenous BR enhances this trend. A high concentration of BR is even more conducive to maintaining the internal stability of the tall fescue’s underground parts. Under drought stress, the tall fescue exhibited high sensitivity to exogenous BR. Exogenous BR significantly influenced the homeostasis regulation mechanism of tall fescue plants, which had a significant impact on the homeostasis of the tall fescue. This indicates that BR plays an important role in the physiological and ecological adaptability of the tall fescue under drought stress (Figure 8).

3.8. Correlation Analysis of Tall Fescue Biomass, Proline Content, Aboveground and Underground Carbon, Nitrogen and Phosphorus Content and Their Metrology Ratios

The correlation analysis of the tall fescue’s index data under different treatments reveals a significant correlation between the carbon, nitrogen, and phosphorus contents in the aboveground and underground parts of the plant and their metrological ratios. The aboveground carbon content showed a positive correlation with the C/N and C/P (p < 0.05), but a negative correlation with the nitrogen content and N/P ratio. The C/N is positively correlated with the C/P and proline, and negatively correlated with the N/P. Additionally, there is a significant positive correlation between the phosphorus content and the C/N, N/P, and the biomass. The nitrogen content shows a positive correlation with the N/P, and a negative correlation with the C/N, C/P, and the proline. There is a significant negative correlation between the C/P and the biomass. Additionally, the ratio of nitrogen to phosphorus was negatively correlated with the biomass and proline. Furthermore, there is a significant positive correlation between the carbon content and the N/P in the underground part. Moreover, the nitrogen content is positively correlated with the phosphorus content and negatively correlated with the C/N and the C/P. The study found that the phosphorus content had a positive correlation with the biomass, but a negative correlation with C/N, C/P, and N/P. Additionally, the C/N was positively correlated with the C/P, but negatively correlated with the N/P and the biomass. The study also revealed a significant positive correlation between the C/P and N/P, and a significant negative correlation between the C/P and the proline. The biomass of the sample is positively correlated with the N/P and negatively correlated with the proline. There is a significant negative correlation between the biomass and proline (Figure 9).

4. Discussion

Biomass is a measure of the internal metabolic changes of plants. The research indicates that BR can increase biomass accumulation by alleviating ROS injury in Pinellia ternata [35] cells. Additionally, other studies have shown that BR can mediate plant growth and physiological metabolic activity in maize tissue under drought stress by increasing the protein synthesis induced by water potential [36]. This study found that drought stress caused a significant decrease in the tall fescue biomass. However, under normal water and mild drought stress, series 2 treatment had a better effect on biomass accumulation, and under severe drought stress, series 1 treatment had a better effect. These results suggest that drought inhibits plant protein synthesis and causes ROS damage, which can reduce the tall fescue biomass [37]. However, BR treatment can alleviate this trend and effectively resist the influence of drought stress.
In organisms, proline is an effective osmotic adjustment substance, as well as a protective substance for biofilms and enzymes, and a free radical scavenger. Therefore, it plays a crucial role in protecting plant growth under stress [38,39]. The study found that the content of proline in the tall fescue increased with the aggravation of stress. This increase may be due to the change in plant water potential under drought stress, which induces the synthesis of proline to adjust the osmotic imbalance caused by water deficiency [40] Additionally, the proline content of the tall fescue increased significantly under the same drought stress level and different concentrations of BR. BR may have initiated the biosynthesis of proline under drought stress, maintaining the osmotic potential and protein structure of plant cells to cope with the negative effects of stress [41]. This suggests that both drought stress and BR can induce proline accumulation in the tall fescue, improving its drought resistance.
Additionally, carbon, nitrogen, and phosphorus are crucial structural elements in plants. The levels of carbon, nitrogen, and phosphorus in a plant can provide valuable information about its physiological state, nutrient status, and the nutrient cycle within an ecosystem [42]. The carbon, nitrogen, and phosphorus contents and stoichiometric ratios in the tall fescue reflect its nutrient utilization strategy and distribution under drought stress with BR addition. Previous research has shown that appropriate concentrations of BR treatment can enhance the accumulation of dry matter and nutrients in maize under high temperature stress [43]. Additionally, studies have shown that exogenous BR spraying treatments can effectively alleviate the senescence process of Fengdan and Ginkgo leaves and delay the chlorophyll degradation rate of plants. This can help improve the photosynthetic capacity and increase the accumulation of dry matter in plants. The current study found that prolonged drought stress reduced the carbon content of the tall fescue over time. Compared to the control group, the carbon content of the tall fescue treated with BR showed improvement, indicating a certain protective effect on the tall fescue [44]. BR may improve the structure and function of the tall fescue’s chloroplast, enhancing its photosynthesis efficiency and increasing its carbon content [45]. Additionally, BR may enhance photosynthase catalytic efficiency by regulating the tall fescue’s stomatal opening and closing [46], leading to improved carbon sequestration and CO2 adsorption from the atmosphere. Simultaneously, BR can regulate the distribution of carbon in plants [47] and allocate fixed carbon from aboveground parts to underground parts to support root elongation. This increases the specific surface area of roots and optimizes water utilization in the substrate. The study found that the carbon content in the underground parts of the tall fescue generally increased with the increasing concentration. Under severe drought stress, the nitrogen content of the tall fescue treated with BR increases significantly. This may be due to BR regulating the opening and closing of stomata, allowing nitrogen-fixing bacteria from outside the plant to enter through the stomata or other means. Subsequently, these bacteria are transported to suitable locations through the vascular system of the tall fescue, forming a symbiotic relationship and providing the plant with additional nitrogen sources. Simultaneously, it regulates the endogenous hormone levels of the tall fescue, enhances its nitrogenase activity [48], and promotes nitrogen absorption by the roots [49]. The study found that treatment with BR increased the phosphorus content of the tall fescue. This may be attributed to the promotion of hydrolysis of organic and inorganic phosphorus in the substrate by increasing the activity of phosphohydrolase and the expression and activity of the phosphorus transporter [50]. As a result, phosphorus became available to plants, the distribution of phosphorus in various parts of plants was regulated, and overall phosphorus accumulation was affected. Additionally, BR has a beneficial regulatory effect on plant root growth and development. A well-developed root structure aids in the efficient absorption of nutrients from substrates.
The stoichiometric ratios of carbon, nitrogen, and phosphorus in the tall fescue reflect its nutrient utilization efficiency and response and adaptation characteristics to environmental changes [51]. Meanwhile, the ratios of carbon to nitrogen and carbon to phosphorus reflect the nutrient absorption efficiency and growth status of plants [52]. According to studies, drought can hinder biological processes, disrupt the distribution of plant nutrients, and reduce nutrient absorption efficiency, ultimately impeding plant growth [53]. The study results indicate that the C/N of the underground part of the tall fescue increased abnormally under drought stress, with the aggravation of drought and the extension of time. However, the aboveground part did not show significant changes. By treating the tall fescue with varying concentrations of BR, the C/N of both aboveground and underground parts increased. This suggests that in the vegetation concrete microenvironment system, the tall fescue is more likely to transport nutrients to its underground parts, promote root development, accelerate nutrient turnover of fine roots [44], strengthen the connection between the underground parts and substrate, and maintain basic life activities while growing slowly under drought stress. The addition of BR improved the problem of nutrient utilization efficiency of the aboveground part of the tall fescue, and at the same time improved the underground nutrient utilization efficiency [54]. Secondly, like the C/N, the C/P of the aboveground part of the tall fescue did not change significantly under stress, while the C/P of the underground part showed a decreasing trend under drought stress, which indicated that plants mainly maintained their life activities by regulating physiological activities of the underground part under drought stress, and drought reduced the phosphorus use efficiency of the tall fescue [55], which could adapt to the drought stress by adjusting their own nutrient distribution. By spraying different concentrations of BR, the C/P in underground parts of the tall fescue increased obviously, which may be due to the fact that spraying BR changed the hormone level of the tall fescue and improved the phosphorus utilization efficiency to cope with the inhibition of drought stress on the growth of the tall fescue, which shows that BR can enhance the stress resistance of the tall fescue, alleviate the damage of drought to the body, and make the body accumulate nutrients and grow slowly under stress. Studies have shown that plant growth is limited by nitrogen when the ratio of nitrogen to phosphorus is lower than 14 [56]. The results of this study show that the N/P in all parts of the tall fescue is lower than 14, which is obviously improved by different concentrations of BR, but the restriction of nitrogen on the growth of the tall fescue has not been lifted, which shows that nitrogen fertilizer should be properly supplemented in the ecological restoration area of vegetation concrete under drought stress, which is beneficial to promote the growth of tall fescue, improve the adaptability of the tall fescue to the drought environment and promote the ecological restoration process of a vegetation concrete ecological restoration system.
The internal stability of plants may change when facing environmental changes, and the ecological stoichiometric internal stability index can reflect the adaptation of plants in the ecological environment [57]. Some research results show that when plants are affected by the outside world, nutrient distribution changes, giving priority to maintaining the internal stability of plant roots, so as to enhance the ability to resist stress [58], which is similar to the research results. With the aggravation of the drought degree and prolongation of the stress time, the response of the aboveground part of the tall fescue in vegetation concrete to BR did not show obvious regularity, while the improvement in the underground part showed that the tall fescue mainly responded to drought stress by maintaining the underground part’s internal stability, so as to achieve the effect of resisting drought stress, which indicated that the tall fescue was in a relatively stable state by regulating nutrient distribution under the action of BR. The results indicated that the underground part of the tall fescue plays a key role in maintaining the stability of the body under stress, and provided an important clue for understanding the adaptation mechanism of plants under drought stress.

5. Conclusions

Drought stress significantly affected the growth of the tall fescue, under different drought stress. BR showed different degrees of promoting the effect on the tall fescue. Under well water supply conditions, spraying 0.2 mg/L of BR is most conducive to the material accumulation and proline synthesis of the tall fescue; under such conditions, the increase in the biomass and proline content of the tall fescue compared to the CK can reach up to 15.50%. When under light drought conditions for 30 days, the proline content ranges from 0.58–0.71 μg/g, and spraying 0.5 mg/L of BR works better, resulting in a 21.60% increase compared to the CK. Under severe drought stress, the result is the same as that under light drought stress, where spraying 0.5 mg/L of BR works better. The contents of C, N, P and their stoichiometric ratios in different organs were different. Spraying 0.2 mg/L, 0.05 mg/L and 0.5 mg/L BR under normal water, mild drought, and severe drought respectively was most beneficial to nutrient accumulation of the tall fescue. Nitrogen is the main factor limiting plant growth in the vegetation concrete ecological restoration system. The tall fescue showed high sensitivity to the exogenous BR input, and the internal stability of the underground part of the tall fescue increased obviously. Therefore, BR can regulate the nutrient absorption strategy of plants, and then improve the resistance of the tall fescue to drought stress, increase the biomass and proline content of plants to a certain extent, and enhance the internal stability of plants; At the same time, in the process of ecological restoration, the supply of nitrogen in soil should be fully considered, and nitrogen should be replenished reasonably.

Author Contributions

Conceptualization, R.K. and M.L.; methodology, S.G. and W.D.; validation, M.L.; investigation, R.K. and W.D.; data curation, R.K.; writing—original draft, R.K. and S.G.; writing—review and editing, W.X., D.X., Y.L. and L.L.; visualization, R.K. and D.X.; funding acquisition, M.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 42207544), the Open Fund of Yangtze River Scientific Research Institute, Changjiang Water Resources Commission (Grant No. CKWV20231190/KY), the Open Fund of the Key Laboratory of Geological Hazards on Three Gorges Reservoir Region, Ministry of Education (Grant No. 2023KDZ11), and the Open Fund of the Hubei Provincial Engineering Research Center for Cement-based Ecological Restoration Technology (Grant No. 2022SNJ09).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Conflicts of Interest

Author Wenhao Dong was employed by the Hubei Runzhi Ecological Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Effects of BR on proline content of tall fescue under different drought stresses.
Figure 1. Effects of BR on proline content of tall fescue under different drought stresses.
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Figure 2. Effects of BR on nitrogen content of tall fescue under different drought stresses.
Figure 2. Effects of BR on nitrogen content of tall fescue under different drought stresses.
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Figure 3. Effects of BR on nitrogen content of tall fescue under different drought stresses.
Figure 3. Effects of BR on nitrogen content of tall fescue under different drought stresses.
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Figure 4. Effects of BR on phosphorus content of tall fescue under different drought stresses.
Figure 4. Effects of BR on phosphorus content of tall fescue under different drought stresses.
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Figure 5. Effects of BR on carbon–nitrogen ratio content of tall fescue under different drought stresses.
Figure 5. Effects of BR on carbon–nitrogen ratio content of tall fescue under different drought stresses.
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Figure 6. Effects of BR on carbon–phosphorus ratio content of tall fescue under different drought stresses.
Figure 6. Effects of BR on carbon–phosphorus ratio content of tall fescue under different drought stresses.
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Figure 7. Effects of BR on nitrogen–phosphorus ratio content of tall fescue under different drought stresses.
Figure 7. Effects of BR on nitrogen–phosphorus ratio content of tall fescue under different drought stresses.
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Figure 8. Effects of different concentrations of BR on the homeostasis of tall fescue under drought stress.
Figure 8. Effects of different concentrations of BR on the homeostasis of tall fescue under drought stress.
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Figure 9. Correlation analysis of tall fescue biomass, proline content, aboveground and underground carbon, nitrogen and phosphorus content and their metrology ratios.
Figure 9. Correlation analysis of tall fescue biomass, proline content, aboveground and underground carbon, nitrogen and phosphorus content and their metrology ratios.
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Table 1. Effects of BR on biomass content of tall fescue under different drought stresses.
Table 1. Effects of BR on biomass content of tall fescue under different drought stresses.
DroughtFacterAboveground BiomassBelowground Biomass
30d60d90d30d60d90d
WWCK18.42 ± 1.87Aa24.96 ± 1.84Aa28.11 ± 0.86Ab15.43 ± 0.93Aa15.72 ± 1.23Aab15.72 ± 1.10Ab
series119.69 ± 1.80Aa27.40 ± 1.90Aa30.70 ± 1.87Aab16.23 ± 0.67Aa16.60 ± 1.46Aab16.93 ± 1.46Aab
series220.22 ± 1.04Aa26.55 ± 1.87Aa31.55 ± 1.90Aa15.64 ± 0.54Aa17.49 ± 1.37Aa18.16 ± 0.85Aa
series318.26 ± 1.46Aa25.88 ± 1.97Aa28.03 ± 1.13Ab13.08 ± 1.70Ab14.26 ± 1.18Ab15.59 ± 0.92Ab
LDCK12.56 ± 1.42Bb20.41 ± 1.65Bab22.90 ± 0.72Bb10.63 ± 1.16Ba10.95 ± 1.37Ba12.54 ± 1.32Bb
series113.19 ± 1.69Bb21.95 ± 1.16Ba24.11 ± 1.30Bab10.73 ± 1.07Ba11.60 ± 1.31Ba12.75 ± 0.75Ba
series216.17 ± 1.55Ba22.54 ± 1.28Ba26.28 ± 1.47Ba11.26 ± 0.84Ba12.90 ± 0.58Ba15.05 ± 1.14Ba
series318.25 ± 1.21Aa18.78 ± 1.98Bb25.37 ± 1.55Bab11.90 ± 1.40Aa12.31 ± 1.06Aa13.79 ± 0.69Bab
SDCK7.95 ± 0.28Ca12.22 ± 1.20Ca19.24 ± 0.48Ab6.09 ± 0.65Ca6.58 ± 0.54Cb7.69 ± 0.23Cb
series18.87 ± 1.51Ca12.55 ± 1.25Ca22.24 ± 0.50Ba6.31 ± 0.55Ca7.94 ± 0.30Cab8.72 ± 0.62Ca
series29.64 ± 1.16Ca13.26 ± 1.62Ca21.71 ± 1.91Ca5.88 ± 0.52Ca8.25 ± 1.03Ba7.32 ± 0.33Cb
series39.24 ± 0.37Ba12.46 ± 1.06Ca20.01 ± 1.17Cab5.49 ± 0.27Ba7.07 ± 0.85Aa7.08 ± 0.71Cb
Note: Different capital letters within indicated that there were significant differences under different drought severity under the same BR concentration at the same time (p < 0.05), and different lowercase letters indicated that there were significant differences under different BR concentration at the same time and the same drought severity (p < 0.05); this is applicable to the following figures and tables as well.
Table 2. Variance analysis of drought time, drought degree and BR concentration on tall fescue carbon, nitrogen and phosphorus contents and stoichiometric ratios in vegetation concrete.
Table 2. Variance analysis of drought time, drought degree and BR concentration on tall fescue carbon, nitrogen and phosphorus contents and stoichiometric ratios in vegetation concrete.
IndexDrought DurationDrought DegreeBrassinolide ConcentrationDrought Duration*Drought DegreeDrought Duration*Brassinolide ConcentrationDrought Degree*Brassinolide ConcentrationDrought Duration*Drought Degree*Brassinolide Concentration
F Valuep ValueF Valuep ValueF Valuep ValueF Valuep ValueF Valuep ValueF Valuep ValueF Valuep Value
CarbonA55.497<0.00116.529<0.00133.769<0.00156.591<0.00115.903<0.00129.475<0.00115.231<0.001
B98.127<0.00181.123<0.00115.320<0.00180.083<0.0015.284<0.00113.252<0.00122.377<0.001
NitrogenA315.868<0.001314.877<0.00129.108<0.00118.708<0.00114.079<0.00156.275<0.00163.480<0.001
B841.029<0.001531.641<0.00156.475<0.001124.314<0.00123.464<0.001177.944<0.00173.259<0.001
PhosphorusA15.188<0.00126.040<0.00114.079<0.0012.1360.0854.2200.0013.8330.0023.2710.001
B1297.468<0.00127.195<0.00116.035<0.00110.359<0.0017.006<0.00174.429<0.0017.009<0.001
C/NA348.527<0.001306.940<0.00196.538<0.00192.816<0.00129.949<0.00164.017<0.00158.337<0.001
B121.398<0.00146.302<0.0016.3810.00158.0670.00115.189<0.00155.842<0.00141.086<0.001
C/PA15.571<0.00139.909<0.00131.168<0.00116.133<0.00110.099<0.0013.9230.0028.478<0.001
B161.970<0.00114.478<0.0014.4490.00613.7580.0062.9200.01321.890<0.0019.166<0.001
N/PA152.367<0.00122.283<0.0012.7210.0514.3080.00413.190<0.00122.340<0.00123.418<0.001
B137.177<0.00170.053<0.00114.384<0.00111.768<0.0013.6660.00359.099<0.00117.008<0.001
BiomassA491.807<0.001514.315<0.00112.571<0.00110.885<0.0012.3630.0391.8910.0941.9580.041
B33.400<0.001737.660<0.00110.124<0.0011.7470.1491.1680.3330.333<0.0010.7790.669
Proline 3914.07 <0.0011417.11 <0.00144.715<0.001141.056<0.0014.968<0.0017.803<0.0017.766<0.001
Note: “A” denotes aboveground; “B” denotes belowground; ”C/N” denotes carbon-to-nitrogen ratio; ”C/P” denotes carbon-to-phosphorus ratio; ”N/P” denotes nitrogen-to-phosphorus ratio.
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Kang, R.; Li, M.; Guo, S.; Xia, D.; Liu, L.; Dong, W.; Xu, W.; Lv, Y. Effect of Brassinolide on Stoichiometric Stability Characteristics of Tall Fescue under Drought Stress in Ecological Restoration. Sustainability 2024, 16, 5942. https://doi.org/10.3390/su16145942

AMA Style

Kang R, Li M, Guo S, Xia D, Liu L, Dong W, Xu W, Lv Y. Effect of Brassinolide on Stoichiometric Stability Characteristics of Tall Fescue under Drought Stress in Ecological Restoration. Sustainability. 2024; 16(14):5942. https://doi.org/10.3390/su16145942

Chicago/Turabian Style

Kang, Roujia, Mingyi Li, Shiwei Guo, Dong Xia, Liming Liu, Wenhao Dong, Wennian Xu, and Yucai Lv. 2024. "Effect of Brassinolide on Stoichiometric Stability Characteristics of Tall Fescue under Drought Stress in Ecological Restoration" Sustainability 16, no. 14: 5942. https://doi.org/10.3390/su16145942

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