Sheep rotational grazing strategy to improve soil organic carbon and reduce carbon dioxide emission from spring wheat in an arid region
Irshad Ahmad
A * , Lina Shi A , Shanning Lou A , Jiao Ning A , Yarong Guo A , Muhammad Kamran A , Wanhe Zhu A and Fujiang Hou A *
A
Abstract
Cultivating forage crops is crucial to improve feed production, and grazing is an important utilisation method to improve soil fertility.
Improving soil organic carbon (SOC) content and reducing carbon dioxide (CO2) emission through grazing management from a spring wheat field.
We compared sheep rotational grazing and control, and studied their effects on SOC and CO2 emission from a spring wheat field.
Sheep rotational grazing improved SOC content (by 23.5%) and soil easily oxidised organic carbon (EOC) content (by 7.7%) and reduces soil microbial biomass carbon (MBC) content (by 35.8%) compared with the control. Sheep rotational grazing reduced CO2 emission compared with the control. Sheep grazing reduced cumulative CO2 emission by 28.9% and 33.0% in May and June compared with the control.
Sheep grazing improved SOC content and reduce CO2 emission from a spring wheat field.
Based on our short-term study, sheep rotational grazing has a significant effect on SOC, EOC and MBC contents and CO2 emission from spring wheat fields in arid regions. For a large-scale assessment of sheep grazing on soil fertility and CO2 emission, more investigation for different soils and climates is necessary. Furthermore, a long-term study is also necessary to better understand the effect of sheep rotational grazing on soil fertility and CO2 emission from spring wheat fields in arid regions.
Keywords: arid regions, carbon dioxide emission, microbial biomass carbon, sheep grazing, soil organic carbon, soil fertility, wheat.
Introduction
Natural grasslands cover an area of about 25% of earth terrestrial ecosystems and provide forages for ruminants, carbon sequestration, water conservation, sand-fixing function and other important ecosystem services (Hopkins and Wilkins 2006; Chen et al. 2017; Hu et al. 2019; Zhao et al. 2020). However, natural grasslands are degrading due to over grazing, climate change and poor management and it is challenging to provide quality feed for livestock production (Wang et al. 2019a; Huang et al. 2021). China has 400 million ha of grassland (Sui and Zhou 2013; Li 2017) and a survey by the Ministry of Environmental Protection, China, suggested that about 31.8% of the grasslands are in a degraded state (Li et al. 2018). Overgrazing due to high stocking rates and static grazing management is an important cause of grassland degradation (Akiyama and Kawamura 2007). Feed shortage in China is increasing due to rapid development of livestock husbandry and therefore it is crucial to improve feed production (Li et al. 2015; Kamran et al. 2022). Cultivating forage crops, especially wheat, is important to cope with feed shortage and improve livestock production and food security (Zeleke 2019; Yang et al. 2022). Cultivating forage crops can not only provide high-quality feed for livestock but also increase soil nutrient storage and improve soil fertility and productivity (Dong and Shen 2000; Sun et al. 2019; Ghani et al. 2022). In China, the total grassland area accounts for 13% of the global grassland, and cultivated grassland represents 1.9% of total grassland (Sui and Zhou 2013; Li 2017). Considering the feed shortage it is important to cultivate forage crops for livestock production in arid regions.
Grazing is an effective strategy to regulate natural grasslands and sown pastures in which animals feed on forage, trampling the soil and returning their excrement to pastures (Wang et al. 2019b; Wei et al. 2021). Grazing maintains healthy development of the ecosystem (Hou et al. 2016). Integrated crop and livestock systems reduce fertiliser usage, improve forage yield and enhance nutrient circulation in the ecosystem (Hatfield et al. 2007; Ferreira et al. 2015). Grazing regulates the interspecific competition between crops and weeds, which hinders the growth and reproduction of weeds in the field, thereby reducing the damage to vegetation by pests and diseases, reducing the use of pesticides and protecting the environment in a healthy manner (Carr et al. 2005). Grazing significantly improved water use efficiency, light use efficiency, carbon and nitrogen content in alpine grasslands (Shen et al. 2019). Livestock feeding on the above-ground parts of vegetation can increase the branching of forage and increase the growth rate, thereby stimulating compensatory growth of forage and increasing the yield (Che et al. 2019). Grazing affects physiological and morphological characteristics of plants as well as soil physico-chemical properties (Zheng et al. 2011; Yang et al. 2019). Therefore, sheep grazing is an effective method to improve soil fertility and forage productivity.
Global climatic change and human activities affect the carbon and nitrogen cycles of terrestrial ecosystems (Yan et al. 2014). The global mean temperature will rise 2–7°C by the end of the century due to increasing greenhouse gas emissions (Allison et al. 2009). China will have a CO2 emission peak before 2030 and China plans to achieve carbon neutrality before 2060 (Xi 2020). According to IPCC (2013), minute changes in the soil organic carbon (SOC) pool affect carbon dioxide (CO2) emission. Sequestration of SOC plays a crucial role in mitigating anthropogenic increase in atmospheric concentration of CO2 (Chen et al. 2018). The SOC is part of the carbon cycle and enhancing SOC stock through sustainable soil carbon sequestration practices can help mitigate climate change (Amelung et al. 2020). The CO2 emission from soil depends on soil respiration and the combination of roots and heterotrophic respiration, and therefore changes in roots and soil microorganisms affect CO2 emission (Hanson et al. 2000). Research suggests that grazing lands are a major sink of carbon; however, improper use of grazing land degrades soil carbon storage capacity and soil health and appropriate grazing results in higher SOC content and improves hydrological function and the soil ecosystem (Kim et al. 2023). Grazing plays a crucial role in the carbon cycle of ecosystems (Zhao et al. 2017; Chen and Frank 2020). Grazing affects the SOC storage by three mechanisms: defoliation, excrement return and trampling (Mikola et al. 2009; Liu et al. 2015). Livestock trampling effects seed germination, seed dispersal, plant cover, plant composition, nutrient cycling and soil physical conditions (Drewry et al. 2008; Horn et al. 2013; Schrama et al. 2013; Ludvíková et al. 2014; Heggenes et al. 2017). Previous research suggested that livestock trampling could increase SOC storage (Liu et al. 2015). The influence of grazing on the soluble SOC content is closely related with the growth season and soil depth (Luo et al. 2009). Grazing can increase the distribution of photosynthetic products in the roots of alpine meadow vegetation and promote the input of photosynthetic products into the soil thereby increasing carbon storage (Hafner et al. 2012). In the grasslands of southern Australia, compared with continuous grazing, long-term grazing rotation increased SOC storage by increasing the vegetation productivity and root turnover rate (Sanderman et al. 2015). Additionally, studies in alpine meadows have proved that grazing can increase carbon storage by stimulating the net ecosystem exchange, and grazing can also reduce CO2 emission by reducing the sensitivity of soil respiration to climate factors (Chen et al. 2015). Thus, sheep rotational grazing is an important utilisation method to improve SOC storage and reduce CO2 emission.
Earlier experiments indicated a limited effect of sheep rotational grazing on SOC content, soil microbial biomass carbon (MBC) content, soil easily oxidised organic carbon (EOC) content and CO2 emission. The objectives of our experiment were to determine the effect of sheep rotational grazing and control treatment on SOC content and CO2 emission in arid regions. The experimental results provide important insights regarding reducing CO2 emission from wheat fields and improvement of soil fertility using sheep rotational grazing.
Materials and methods
Experimental site, experimental design and field management
A field experiment was conducted at the Linze Grassland Agricultural Experimental Station of Lanzhou University, China (100°02′E, 39°15′N; 1390 a.s.l.) in the 2018 growth season. The experimental station is located in the core area of the Hexi corridor Hei-he Oasis in the inland arid area of northwest China, with the Qilian Mountains in the south and the Alxa Desert in the north. The experimental area is a salinised meadow area. The soil of the experimental site was classified as Aquisalids according to United States Department of Agriculture soil taxonomy (Ning et al. 2020). Soil pH of the experiment site was 8.5 and salt contents were 0.6–0.9% (Ghani et al. 2022). The soil electrical conductivity was 4.2 dS m−1. The experimental site is an arid area having deficit and erratic precipitation (Fig. 1). The annual precipitation of the site was 118.4 mm. The precipitation is concentrated in May–September and accounts for more than 70% of total annual precipitation. Evaporation of the experimental site was 1830.4 mm. The annual average temperature is 7.7°C, annual sunshine hours are 3042 and the frost-free period is about 170 days. Monthly precipitation and monthly average temperature during the growth season were measured using an automatic weather station (Fig. 1). The main agricultural systems in the study area are specialised intensive crop production and extensive integrated crop–livestock production (Hou et al. 2008). The nutrient status of the top 0–20 cm soil layer of the site comprised 10.2 g kg−1 SOC, 4.8 g kg−1 EOC, 208.3 mg kg−1 MBC, 0.80 g kg−1 total soil nitrogen, 0.85 g kg−1 soil total phosphorus and 0.50 g kg−1 soil total potassium.
Mean temperature (°C) and precipitation (mm) for January–December 2018 at the experimental site.
The field experiment had a randomized complete block design with three replications. There were two treatments: sheep grazing (RG) and control (CK). Spring wheat (Yong-Liang No. 15), which is commonly grown for forage production in arid regions, was sown in March 2018 at a seed rate of 300 kg ha−1. Each single plot had an area of 1 ha. The inter row spacing was 10 cm. Nitrogen (urea, 46% N) was applied at the time of sowing at a rate of 225 kg N ha−1 (Guo et al. 2023) and phosphorus (calcium superphosphate, 16% P2O5) at 75 kg ha−1. These are the recommended rates of nitrogen and phosphorus for wheat in this area. Sheep grazing was carried out at a stocking rate of 80 adult sheep ha−1 at stem elongation stage (BBCH-30). Sheep grazing was carried out at two times. The grazing time in the wheat field was from May (1–5 May) to June (1–5 June). Each grazing time was 5 days, and the grazing time interval was about 25 days. In the middle of each plot we constructed a wire fence to isolate a 10 m × 10 m plot as CK. The field was irrigated (120 mm) once in April.
Sampling and measurements
Dry matter yield (g m−2) was measured in May (20 days after first sheep grazing), June (20 days after second sheep grazing) and July (40 days after second sheep grazing) in RG and CK treatments in 2018. At three different locations in each replication, a 1 m2 area was cut at ground level. The samples were oven dried at 75°C to a constant weight. An electronic balance was used to measure the dry matter yield.
The SOC, MBC and EOC contents were measured in May (20 days after first sheep grazing), June (20 days after second grazing) and in July (40 days after second grazing) during the 2018 growth season. Soil samples from 0–10, 10–20 and 20–30 cm soil depths at three different locations in each replication were taken with an auger. The SOC content was determined using the potassium dichromate sulfuric acid oxidation method (Wang et al. 2014a); MBC content was assayed as described by Zeng et al. (2015); and EOC content was assayed by potassium permanganate oxidation method (Wang et al. 2014b).
The CO2 emission was measured during May and June. The measurements were carried out during 6–10 May, 11–20 May, 21–30 May, 6–10 June, 11– 20 June and 21–June from 0 to 24 h. The 8150 Multiplexer Soil Carbon Flux Automatic Monitoring System 8100-104 (LI-COR USA), a long-term CO2 emission measurement system, was used to monitor the CO2 emission fluxes. Taking 0–24 h as a measurement cycle, the air chamber was automatically closed once every 30 min, and the closing time was 1.5 min. The system automatically recorded the changes in CO2 fluxes and we used the Li-8100-201 temperature sensor and Li-8100-204 ML 2x soil moisture sensor to monitor the 5 cm soil-depth temperature and moisture. One day before each measurement, in order to avoid the impact of installation of the air chamber on soil respiration, a polyvinyl chloride respiration measurement ring was inserted in the soil in advance. The inner diameter and height of the ring were 10 and 12 cm, respectively. The height of the measuring ring exposed to the ground was adjusted by artificially adjusting the height of the air chamber, which was generally about 5–8 cm.
Statistical analysis
Analysis of variance was determined with SPSS 19.0 software (SPSS, Inc., Armonk, USA). The data obtained from each sampling event were analysed separately. Mean comparison was carried out with Tukey’s test at P ≤ 0.05. Pearson’s correlations were calculated to determine the relationship of CO2 fluxes with soil temperature and soil moisture.
Results
Dry matter yield
Dry matter yield of spring wheat significantly differed for the RG and CK treatments (Fig. 2). The dry matter yield in RG and CK treatments increased from May (20 days after first sheep grazing) to July (40 days after second grazing), and maximum dry matter yield was in July (40 days after second grazing). The dry matter yield was higher in the CK than the RG treatment. The RG treatment decreased dry matter yield in May (20 days after first grazing) by 49.4 g m−2, in June (20 days after second grazing) by 79.7 g m−2 and in July (40 days after second grazing) by 91.4 g m−2 compared with the CK treatment.
SOC and its components
Sheep grazing significantly improved SOC content compared with the CK treatment (Fig. 3). The SOC content was high at 0–10 cm soil depth and then reduced with greater soil depth. The SOC content increased from May (20 days after first grazing), reached to its maximum in June (20 days after second grazing) and then decreased in July (40 days after second grazing). Means based on three stages’ data showed that sheep grazing significantly increased SOC content at 0–10 cm soil depth by 23.5%, at 10–20 cm depth by 21.4% and at 20–30 cm depth by 25.6% compared with CK treatment.
Effects of sheep rotational grazing (RG) and control treatment (CK) on the soil organic carbon content at 0–10, 10–20 and 20–30 cm soil depths of spring wheat at 20 days after first sheep grazing and 20 and 40 days after second sheep grazing. Vertical bars represent means ± s.d. (n = 3). Analyses were done separately for different grazing intervals and different soil depths.
Sheep grazing significantly reduced the MBC content compared with CK treatment (Fig. 4). The MBC content was high at 0–10 cm soil depth. The MBC content was higher in May (20 days after first grazing), decreased in June (20 days after second grazing) and then increased in July (40 days after second grazing). Means based on May, June and July data showed that RG significantly reduced MBC content at 0–10 cm soil depth by 35.9%, at 10–20 cm by 33.0% and at 20–30 cm by 38.5% compared with CK treatment.
Effects of sheep rotational grazing (RG) and control treatment (CK) on the soil microbial biomass carbon content at 0–10, 10–20 and 20–30 cm soil depth of spring wheat at 20 days after first sheep grazing and 20 and 40 days after second sheep grazing. Vertical bars represent means ± s.d. (n = 3). Analyses were done separately for different grazing intervals and different soil depths.
The EOC content was higher in RG compared with CK treatment (Fig. 5). The EOC content was higher in the 0–10 cm soil layer, followed by 10–20 cm and then 20–30 cm. Means based on May, June and July data showed that RG increased EOC content at 0–10 cm soil layer by 4.9%, at 10–20 cm by 13.6% and at 20–30 cm by 4.5% compared with CK treatment.
Effects of sheep rotational grazing (RG) and control treatment (CK) on the soil easily oxidised organic carbon content at 0–10, 10–20 and 20–30 cm soil depth of spring wheat at 20 days after first sheep grazing and 20 and 40 days after second sheep grazing. Vertical bars represent means ± s.d. (n = 3). Analyses were done separately for different grazing intervals and different soil depths.
Sheep grazing significantly reduced CO2 emission from the spring wheat field compared with CK treatment (Fig. 6). The CO2 emission fluxes peaks all appeared around 2:00 PM. The daily dynamics of CO2 emission in RG and CK treatments showed a trend of simultaneous change. The average CO2 emission in RG treatment was 4.9 (6–10 May), 5.7 (11–20 May) and 6.5 (21–30 May) μmol m−2 s−1 and correspondingly in CK was 6.4, 7.4 and 8.1 μmol m−2 s−1. The average CO2 emission in RG treatment was 5.6 (6–10 June), 5.2 (11–20 June) and 5.1 (21–30 June) μmol m−2 s−1 and correspondingly in CK was 7.0, 8.0 and 6.9 μmol m−2 s−1.
Effects of sheep rotational grazing (RG) and control treatment (CK) on carbon dioxide emission from a spring wheat field for 6–10 May (May, a), 11–20 May (May, b), 21–30 May (May, c), 6–10 June (June, a), 11–20 June (June, b) and 21–30 June (June, c) from 0 to 24 h. Vertical bars represent means ± s.d. (n = 3). Data of May (a) and June (a) are means of 5 days whereas data of May (b), June (b), May (c) and June (c) are means of 10 days.
The RG and CK treatments showed significantly different cumulative CO2 emission from the spring wheat field (Fig. 7). The CK treatment had higher cumulative CO2 emission in May and June compared with RG treatment. The cumulative CO2 emission in May and June in CK treatment was 228.1 and 217.9 g CO2 m−2 month−1, respectively, and correspondingly in RG treatment was 177.0 and 163.7 g CO2 m−2 month−1. Sheep grazing reduced the cumulative CO2 emission in May by 28.9% and in June by 33.0% compared with CK treatment.
During the spring wheat growth season, the CO2 fluxes showed an exponential increase with increases in soil temperature and moisture (Fig. 8). Soil temperature and moisture were significantly positively correlated with CO2 fluxes. In May and June, during the monitoring period of the two treatments of wheat field, the R2 value of CO2 flux against soil temperature was higher than that for soil moisture, but the influence of soil moisture on CO2 flux in May was higher than that of soil temperature (P < 0.001 vs P < 0.05).
Discussion
Effect of sheep rotational grazing on SOC content and its components
Soil is the biggest carbon pool of grassland ecosystem and stores 28–37% of the carbon in the terrestrial ecosystem (Lal 2004a; Tang et al. 2018; Zhang et al. 2018). The increase of storage or sequestration of SOC content is important to improve soil fertility and crop productivity as well as mitigate the CO2 increase in the atmosphere (Lal 2004b; Wiesmeier et al. 2019). The SOC content reflects the long-term stability between accumulation and loss of organic carbon and is affected by human activities, land use, precipitation and microbial metabolism (Piao et al. 2009; Yang et al. 2012). Grazing is an important strategy to utilise cultivated grasslands by improving soil fertility and environmental quality (Šimek and Čuhel 2009; Ehsanul 2016). Grazing significantly influences SOC storage in grasslands (Hao et al. 2024). Long-term grazing rotation can increase SOC storage by increasing vegetation productivity and root turnover rate (Sanderman et al. 2015). In our study, the RG treatment significantly increased SOC content compared with CK. A possible reason is that sheep trampling enhanced the decomposition of litter and converted it into soil organic matter (Ball et al. 2012). An other possible reason is that livestock feeding on forage changes the pattern of vegetation carbon allocation, promoting the transfer of photosynthetic products to the root system and providing a rich substrate for the formation of soil organic matter (Piñeiro et al. 2010; Hafner et al. 2012). A third possible reason is that the sheep excrement return during grazing improved the SOC content. Research suggests that grazing increases the SOC content (Han et al. 2014). The MBC is an index indicating any SOC content changes due to land use or management measures, and its content generally accounts for 1–4% of the soil organic matter (Allen et al. 2010). The MBC is a crucial indicator of changes of soil quality as well as management practices and is sensitive to environmental changes (Holt 1997; Wang and Long 2008). Liu et al. (2012) showed that grazing increased SOC, MBC and total nitrogen contents in typical steppe and desert steppe ecosystems in China. However, our results suggested that SOC content was increased and MBC content decreased in RG compared with CK treatment. The possible reason for lower MBC content in sheep grazing treatment is that sheep trampling increases the soil compactness and decreases soil porosity, soil permeability and water-stable aggregates and thus changes the living environment of microorganisms, which in turn disturbs microorganism metabolism and reproduction, reducing their activity and ultimately leading to lower MBC content (Chai et al. 2016; Tong et al. 2018). Xu et al. (2023) showed that the soil microbial biomass and enzyme activities reduced with increases in grazing intensity and duration. In our study, MBC content of the surface soil was higher compared with deeper soil layers, and surface soil contains more microorganisms than deeper soil layers. The SOC content was also higher in the surface soil compared with deeper soil layers, and the soil porosity is high and the oxygen sufficient, which are conducive for survival of microorganisms (Niu et al. 2013). Rui et al. (2011) suggested that Tibetan sheep grazing increased the organic matter of surface soil of alpine meadow but reduced the MBC content at 20–30 cm soil depth. The EOC content under RG treatment was not much higher than for CK. A possible reason is that EOC content is an unstable part of the SOC, and the effect of grazing on EOC content is not obvious; it may also be related to the quality of litter entering the soil (Wen et al. 2016). The higher EOC content in the top 0–10 cm soil depth in RG treatment was attributed to sheep excrement return during grazing.
Effects of sheep rotational grazing on CO2 emission and its relation with soil moisture and temperature
Soil respiration is an important process in the global carbon cycle and plays an important role in altering CO2 levels in the atmosphere (Li et al. 2024). Soil respiration is composed of three parts – root respiration, microorganism respiration and soil animal respiration – with the first two accounting for about 90% of soil respiration (Chen et al. 2011). Grazing animals feeding, trampling and their excreta return directly or indirectly result in greenhouse gas emissions and global warming (IPCC 2007; Treweek et al. 2016). The RG treatment significantly reduced CO2 emission and cumulative CO2 emission compared with CK. Previous study showed that grazing reduced soil respiration rate compared with no-grazing treatment (Jia et al. 2007); furthermore, the mean soil respiration rate in no-grazing and grazing treatments was 247.9 and 108.3 mg CO2 m−2 h−1, respectively. Moreover, the higher soil respiration in no-grazing treatment was attributed to higher biomass and soil moisture content. Cui et al. (2000) reported that grazing reduced CO2 emission in Stipa grandis grasslands. Previous research suggested that summer grazing decreased CO2 concentration in desert and typical temperate steppe ecosystems, whereas it increased in meadow (Shi et al. 2017). Furthermore, N2O emission increased in meadow but was not significantly higher than for desert and typical temperate steppe ecosystems. Our results are consistent with those of Jia et al. (2007), who found that grazing significantly reduced CO2 emission in typical Leymus chinensis steppes in Inner Mongolia. The possible reason for low CO2 emission in sheep grazing treatment is that long-term sheep trampling compacts the soil and reduces its porosity, which in turn reduces soil hydraulic conductivity, and thus the decrease in soil water content reduces respiration rate and CO2 emission (Ball et al. 2012; Chen et al. 2013). Another possible reason for low CO2 emission is that RG treatment had lower vegetation coverage and the soil was more exposed, which accelerated the evaporation and loss of soil water; at the same time the increase in the area of grassland exposed to light makes the change in soil temperature more obvious and the CO2 emission is significantly reduced (Jia et al. 2007). Furthermore, grazing reduces the existing stock on the ground, reduces the photosynthetic rate and supplies more photosynthetic products to the above-ground parts, which reduces root biomass, weakens root respiration and reduces CO2 emission (Gong et al. 2014). Our findings are inconsistent with those of Liu et al. (2016), likely because of differences in the grazing system, forage type and soil moisture status. Chen et al. (2015) suggested that in alpine meadow, grazing can increase carbon storage by stimulating net ecosystem exchange, and also reduce system CO2 emission by reducing the sensitivity of soil respiration to climate factors. In western Canadian grasslands, grazing reduced CO2 emissions from sandy soil (Thomas et al. 2018). Our study showed significantly reduced CO2 emission for RG compared with CK treatment. The CO2 fluxes were affected by soil temperature and moisture. The CO2 fluxes increased exponentially with increased soil temperature and moisture, consistent with results of Zhao et al. (2016). The daily dynamics of CO2 fluxes are related to the daily changes in soil temperature. During the day, solar radiation reaches its maximum at about 2:00 PM and at this time the soil temperature is almost at its peak. The increase in temperature can promote plant root respiration, speed up metabolism of related microorganisms in the soil, stimulate enzyme activity and thus cause more CO2 emission (Huang et al. 2005; Johnston and Sibly 2018; Nissan et al. 2023). Many studies have shown a quadratic, exponential or linear relationship of soil moisture and soil temperature with CO2 fluxes (Zhou et al. 2013; Gong et al. 2014). Our findings indicated that sheep grazing is an important strategy to improve soil fertility and reduce CO2 emission in arid regions.
Conclusion
In this experiment, sheep grazing affected SOC, EOC and MBC contents, CO2 emission and dry matter yield of wheat. Sheep grazing resulted in higher SOC and EOC contents but lower MBC content. The CO2 emission and cumulative CO2 emission were also lower for the sheep grazing treatment. The results are important for improving the SOC, EOC and MBC contents and reducing CO2 emission from spring wheat in arid regions. In our short-term study, sheep rotational grazing had a significant effect on SOC, EOC and MBC contents and CO2 emission from a spring wheat field in an arid region. More investigation using different soils and climates is necessary for a large-scale assessment of effects of sheep grazing on soil fertility and CO2 emission. Furthermore, a long-term study is required to better understand the sheep grazing impact on soil physico-chemical properties, greenhouse gas emissions and soil microbial community structure in arid regions.
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declaration of funding
This research work was supported by the Program for Innovative Research Team of Ministry of Education (IRT_17R50), the Program of National Science and Technology Assistance (KY202002011), the China Postdoctoral Science Foundation (2021M701521) and Lanzhou City’s Scientific Research Funding Subsidy to Lanzhou University.
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