Northern China's Grasslands Research Articles

Responses of Soil Enzyme Activity to Long-Term Nitrogen Enrichment and Water Addition in a Typical Steppe

Enzyme activity plays an important role in soil biochemical processes and is a key factor driving nutrient cycling. Although a great number of studies examined the effects of nitrogen (N) enrichment and water (W) addition on soil enzyme activity, most of them focused on the effect of only one resource and are based on short-term investigations. The separate and interactive effects of long-term changes in nitrogen and water on soil enzyme activity remain largely unexplored. In this study, we demonstrated the responses of two types of soil enzyme, β-1,4-glucosidase (BG) and acid phosphatase (APA), to increased nitrogen and water based on a 16-year experiment conducted in a typical grassland in northern China. The results show that: (1) nitrogen addition inhibited BG and APA in 2019 and 2020; (2) water addition had no significant effect on BG activity, but significantly reduced APA activity in 2020; and (3) redundancy analysis (RDA) showed that nitrogen and water addition affected soil enzyme activity mainly by affecting soil microbial biomass carbon (MBC). The present research offers a comprehensive explanation of how atmospheric nitrogen deposition and precipitation patterns affect the characteristics of microorganisms and the cycling of nutrients in grassland ecosystems.

Short-term legacy effects of long-term nitrogen and water addition on soil chemical properties and micro-bial characteristics in a temperate grassland.

Nitrogen deposition and summer precipitation in eastern Inner Mongolia are predicted to increase in recent decades. However, such increases in nitrogen inputs and precipitation may not be continuous under the future new patterns of global change, with the direction and magnitude of which may change or weaken. The legacy effects of nitrogen and water addition after cessation on ecosystems are still unclear. Based on a 13-year nitrogen and water addition experiment in temperate grassland of northern China, we examined the short-term (2 years) legacy effects of historical nitrogen and water addition on soil physicochemical properties and microbial properties after the cessation of nitrogen and water addition in the 14th year. The results showed that the positive effects of historical nitrogen addition on most of soil nutrient variables diminished after two years of cessation, including ammonium nitrogen, nitrate nitrogen, dissolved organic carbon and nitrogen, and Olsen-P concentrations. In contrast, there were legacy effects on soil microbial characteristics. For example, the historical nitrogen input of 15 g N·m-2·a-1 reduced microbial biomass carbon, respiration, and alkaline phosphomonoesterase activity by 73.3%, 81.9%, and 70.3% respectively. It implied that microbial parameters restored slowly in comparison with soil nutrients, showing a hysteresis effect. Results of Pearson's correlation and redundancy analysis showed that the legacy effects of historical nitrogen addition on microbial parameters could be attributed to the negative effects of nitrogen addition on soil pH. Historical water addition showed significant legacy effects on soil pH, ammonium nitrogen, dissolved organic carbon and nitrogen, respiration, and soil enzyme activities, which significantly interacted with historical nitrogen addition. These results are of great significance to predict the changes in grassland ecosystem functions and services under the local environmental improvement conditions, and to reveal the restoration mechanism of degraded grassland.

A dataset of observational key parameters in carbon and water fluxes in a semi-arid steppe, Inner Mongolia (2012 – 2020): based on a long-term manipulative experiment of precipitation pattern

Warming has led to remarkable changes in global precipitation pattern, which will significantly affect vegetation growth and ecosystem function of the semiarid grasslands in Northern China. As a key processe of ecosystem function, carbon and water flux determines the carbon sequestration capability and resource utilization strategies of ecosystems. Therefore, understanding the responses of ecosystem carbon and water fluxes to precipitation pattern changes and their controls will be helpful for the evaluation in the carbon sequestration capacity of grassland ecosystems. However, there is a lack of long-term experiments and observational data on the responses of carbon and water processes to precipitation pattern changes in grassland ecosystems. Based on the long-term precipitation pattern manipulative experiment (including seven precipitation amount and rain event frequency treatments), we collected seasonal dynamics of ecosystem carbon and water fluxes by the static chamber method connecting with infrared gas analyzer during 2012-2020 in Xilin Gol grassland, Inner Mongolia. The dataset consists of two data files, namely the meteorological environmental data file (including annual precipitation, air temperature, soil moisture, and soil temperature) and the carbon and water fluxes data file (including ecosystem gross primary productivity, ecosystem respiration, net ecosystem carbon exchange, evapotranspiration, carbon use efficiency, and water use efficiency). Preliminary data analysis has shown that the drought treatment could significantly reduce the carbon and water fluxes, while water addition treatment had no significant effect on them. All the parameters recovered to the control level in the first year after the treatment cessation. This dataset is expected to provide important data support for the understanding of the responses of carbon and water cycles and their coupling processes to future precipitation regime in grasslands of Northern China.

Precipitation regime changes alter allometry and plasticity of meristem allocation in annual herbaceous plants in a semiarid sandy grassland, northern China

AbstractThe three principal fates of axillary meristem in flowering plants are growth (G), reproduction (R), and inactivity (I). The allocation relationships between each meristem and plant size in annual herbaceous plants tend to change with altered precipitation (P) patterns in arid and semiarid grasslands. Here, we examined the allometry and plasticity of meristem allocation in three dominant annual herbaceous plants: Setaria viridis, Corispermum macrocarpum, and Bassia dasyphylla in a semiarid sandy grassland in northern China. We determined the range of plant sizes for each of the three species in the following treatments: ambient environment (Amb), P increased by 30% (P[+]) and by 60% (P[++]), P decreased by 30% (P[−]) and by 60% (P[− −]), drought for 46 days from May 1st to June 15th (D1) and from July 1st to August 15th (D2). We found that meristem allocation to branching intensity increased while allocation to apical dominance decreased with increasing plant size under decreased precipitation and seasonal drought. Decreased precipitation and seasonal drought caused the slope of allometry of meristem allocation in the three species to be significantly different from 1. Plasticity of meristem allocation to G, R, and I in S. viridis tended to be significantly greater in August under P(+) and P(++) while in C. macrocarpum tended to be greater in July under P(−), P(− −), D1, and D2. Our findings are important components of an adaptive strategy in annual herbaceous plants throughout the development stage, which will contribute to predict their developmental dynamics in the semiarid sandy grassland under future climate change.

Aridity and decreasing soil heterogeneity reduce microbial network complexity and stability in the semi-arid grasslands

Soil microbes play vital roles in mediating the functions and services of terrestrial ecosystems in the context of ongoing climate change and human disturbance. There are complex interactions between soil microbial taxa. However, research on the drivers of soil microbial network complexity and stability based on microbial taxa interactions is still in its infancy. We examined network structure and the complexity and stability of soil microbial communities across a large-scale environmental gradient in semi-arid grasslands of northern China by combining network theory and high-throughput sequencing. We found that aridity was the strongest driver of soil microbial network structure. Increasing aridity directly reduced the complexity and stability of soil microbial networks by decreasing the ratio of microbial taxa that participated in network construction and the ratio of potential positive and negative interactions of networks. Soil heterogeneity enhanced microbial network complexity and stability by potentially promoting diverse host plants and mediating uneven distribution of soil resources. These findings suggest that aridity and decreasing soil heterogeneity may have detrimental influences on soil microbial functions and the associated plant performance. This study provides new insights into the controls of climatic and/or edaphic variables in regulating soil microbial networks and highlights the importance of environmental heterogeneity in community assembly mechanisms of soil microbes.

Biotic and abiotic drivers of ecosystem multifunctionality: Evidence from the semi-arid grasslands of northern China

Ecosystem functioning plays a crucial role in maintaining human welfare. Terrestrial ecosystems provide multiple ecosystem services simultaneously, such as carbon sequestration, nutrient cycling, water purification, and biodiversity conservation, known as ecosystem multifunctionality (EMF). However, the mechanisms by which biotic and abiotic factors, and their interactions regulate EMF in grasslands are unclear. We conducted a transect survey to illustrate the single and combined effects of biotic factors (including plant species diversity, trait-based functional diversity, community-weighted mean (CWM) of traits, and soil microbial diversity) and abiotic factors (including climate and soil) on EMF. Eight functions were investigated, including aboveground living biomass and litter biomass, soil bacterial biomass, fungal biomass, arbuscular mycorrhizal fungi biomass, and soil organic carbon storage, total carbon storage and total nitrogen storage. We detected a significant interactive effect between plant species diversity and soil microbial diversity on the EMF; Structural equation model showed that soil microbial diversity indirectly affected EMF by regulating plant species diversity. These findings highlight the importance of the interaction effect of above- and below-ground diversity on EMF. Both plant species diversity and functional diversity had similar explanatory power for the variation in EMF, implying that niche differentiation and multifunctional complementarity among plant species and traits are essential in regulating the EMF. Furthermore, the effects of abiotic factors on EMF were stronger than those of biotic factors via direct and indirect pathways affecting above- and below-ground biodiversity. As a dominant regulator, the soil sand content was negatively correlated with EMF. These findings indicate the vital role of abiotic mechanisms in affecting EMF, and deepen our understanding of the single and combined effects of biotic and abiotic factors on EMF. We conclude that soil texture and plant diversity, representing crucial abiotic and biotic factors, respectively, are important determinants of the EMF of grasslands.

Arbuscular mycorrhizal fungi alter plant N and P resorption of dominant species in a degraded grassland of northern China

Plant nutrient resorption is an important regulator of biogeochemical cycling and decomposition. Arbuscular mycorrhizal fungi (AMF) may influence this process by helping plants absorb nutrients, although the mechanism by which this occurs remains unclear. We examined variations in nutrient resorption over a period of 3 years in three dominant species, namely, Artemisia frigida, Potentilla acaulis, and Stipa krylovii, treated with or without fungicide in a degraded grassland in Inner Mongolia in 2017. Our results showed that AMF increased the nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) in A. frigida but decreased NRE and PRE in S. krylovii and PRE in P. acaulis. The inconsistent nutrient resorption responses of A. frigida and S. krylovii to AMF were primarily attributed to the changes in biomass in the presence of AMF, thereby changing the nutrient requirements. For P. acaulis, the reduction in PRE with AMF was because AMF-induced its N limitation, which is consistent with the relative nutrient resorption hypothesis. AMF increased internal nutrient cycling in A. frigida, which may promote its dominance in degraded grassland in Inner Mongolia, China. Moreover, AMF reduced senesced leaf N concentrations, thereby reducing the carbon (C):N ratio in senesced leaves, which may affect nutrient return to the soil. Our findings indicate that AMF substantially affect the biomass and nutrient requirements of dominant plant species, potentially leading to changes in nutrient resorption during grassland degradation, which may provide a deep insight into plant nutrient retranslocation in degraded grasslands.

Prescribed fire alters nematode communities in an old-field grassland.

Fire is a common disturbance in many biomes, with both beneficial and detrimental effects on soil biology, which largely depend on fire intensity. However, little is known about the impact of fire on soil nematode communities in terrestrial ecosystem. In the present study, we investigated the effects of short-term prescribed fire on soil nematode communities and soil properties in an old-field grassland in Northern China. The results showed that burning significantly increased soil nematode abundance by 77% and genus richness by 49% compared to the control. Burning also decreased taxon dominance by 45% (Simpson's D) and increased nematode diversity by 31% (Shannon-Weaver H'). However, burning increased plant parasites (particularly genera Cephalenchus and Pratylenchus) and shifted community to more bacterial-feeding genera (i.e., decreased Channel Index). Generally, burning increased soil bio-available nitrogen (NH4 +-N and NO3 --N) content, which would be the main drivers causing nematode community to flourish via a "bottom-up" effect. These results suggest that prescribed fire increases nematode diversity and alters community composition toward more plant parasites and bacterial feeders. Our findings highlight the importance of prescribed fire management in shaping short-term nematode community structure and function, but the long-term effects and impacts of these changes on soil nutrient and carbon cycling remain unknown.

Higher N Addition and Mowing Interactively Improved Net Primary Productivity by Stimulating Gross Nitrification in a Temperate Steppe of Northern China.

Anthropogenic disturbance, such as nitrogen (N) fertilization and mowing, is constantly changing the function and structure of grassland ecosystems during past years and will continue to affect the sustainability of arid and semiarid grassland in the future. However, how and whether the different N addition levels and the frequency of N addition, as well as the occurrence of mowing, affect the key processes of N cycling is still unclear. We designed a field experiment with five levels of N addition (0, 2, 10, 20, and 50 g N m-2 yr-1), two types of N addition frequencies (twice a year added in June/November and monthly addition), and mowing treatment in a typical grassland of northern China. The results showed that higher N addition and mowing interactively improved net primary productivity (NPP), including aboveground and belowground biomass, while different N addition frequency had no significant effects on NPP. Different N addition levels significantly improved gross ammonification (GA) and nitrification (GN) rates, which positively correlated to aboveground net primary productivity (ANPP). However, the effect of N addition frequency was differentiated with N addition levels, the highest N addition level (50 g N m-2 yr-1) with lower frequency (twice a year) significantly increased GA and GN rates. Mowing significantly increased the GA rate but decreased the GN rate both under the highest N addition level (50 g N m-2 yr-1) and lower N addition frequency (twice a year), which could improve N turnover by stimulating plant and microbial activity. However, a long-term study of the effects of N enrichment and mowing on N turnover will be needed for understanding the mechanisms by which nutrient cycling occurs in typical grassland ecosystems under global change scenarios.

Characteristics of Mercury Fluxes between Soil and Air in the Farming-Pastoral Ecotone of Songnen Grassland

In order to understand the characteristics and influencing factors of surface release fluxes in the typical agro-pastoral mosaic region of the Songnen grasslands of northern China, this study selected two sample plots to, respectively, represent the L. chinensis covered grassland (L), and the Z. mays covered fields (Z) in the Waizi area of Changling County, with western Jilin Province as the study area. This study investigated the atmospheric mercury (Total Gaseous Mercury (TGM)) concentrations, surface soil mercury concentrations, the gaseous elemental mercury exchange fluxes, and related environmental factors. The results showed that the TGM concentrations in two sample plots in the study area were basically the same during the summer and autumn months, but were higher in summer than in autumn, and there was a clear diurnal pattern. The average mercury concentrations in the surface soil were also higher in summer than in autumn. Furthermore, the surface soil has a clear mercury release process, and the mercury release were higher in the sheep grass field than the maize field during the same season. The mercury release fluxes in each site within the ecotone were related to the solar radiation and soil temperature values, and the effects of them on the soil mercury release were independent from one another.

Seasonal precipitation regulates magnitude and direction of the effect of nitrogen addition on net ecosystem CO2 exchange in saline-alkaline grassland of northern China

Increased nitrogen (N) deposition and altered precipitation regimes have profound effects on carbon (C) flux in semi-arid grasslands. However, the interactive effects between N enrichment and precipitation alterations (both increasing and decreasing) on ecosystem CO2 fluxes and ecosystem resource use efficiency (water use efficiency (WUE) and carbon use efficiency (CUE)) remain unclear, particularly in saline-alkaline grasslands. A four-year (2018–2021) field manipulation experiment was conducted to investigate N enrichment and precipitation alterations (decreased and increased by 50 % of ambient precipitation) and their interactions on ecosystem CO2 fluxes (gross- ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO2 exchange (NEE)), as well as their underlying regulatory mechanisms under severe salinity stress in northern China. Our results showed that N addition and precipitation alteration alone did not significantly affect the GEP, ER and NEE. While the interaction of N addition and increased precipitation over the four years significantly improved the mean GEP and NEE by 24.9 % and 15.9 %, respectively. The interactive effects of N addition and increased precipitation treatment significantly stimulated the mean value of WUE by 39.1 % compared with control, but had no significant effects on CUE over the four years. Based on the four-year experiment, the magnitude and direction of the effects of N addition on the NEE were related to seasonal precipitation. Nitrogen addition increased the NEE under increased precipitation and decreased it during extreme drought. Soil salinization (pH and base cations) could directly or indirectly affect GEP and NEE via plants productivity, plant communities, as well as ecosystem resource use efficiency (WUE and CUE) based on structural equation model. Our results address lacking investigations of ecosystem C flux in saline-alkaline grasslands, and highlight that precipitation regulates the magnitude and direction of N addition on NEE in saline-alkaline grasslands.

Autumn nitrogen enrichment destabilizes ecosystem biomass production in a semiarid grassland.

Nitrogen (N) deposition decreases the temporal stability of ecosystem aboveground biomass production (ecosystem stability). However, little is known about how the responses of ecosystem stability differ based on seasonal N enrichment. By adding N in autumn, winter, or growing season, from October 2014 to May 2020, in a temperate grassland in northern China, we found that only N addition in autumn resulted in a significantly positive correlation between ecosystem mean aboveground net primary productivity (ANPP) and its standard deviation and significantly reduced ecosystem stability. Autumn N-induced reduction in ecosystem stability was associated with the vanished negative effect of community-wide species asynchrony (asynchronous dynamics among populations to environmental perturbations) on the standard deviation of ecosystem ANPP in combination with the emerged positive effect of dominance (Simpson's dominance index that indicates the relative weight of dominant species in a community). Our findings indicate that autumn N addition might overestimate the negative effect of annual atmospheric N deposition on ecosystem stability, suggesting that to better evaluate the influence of N deposition in temperate grasslands, both field experiments and global modeling should consider not only the annual N load but also its seasonal dynamics. Moreover, further studies should pay more attention to the alteration in the ecosystem temporal deviations, which might be more sensitive to human-induced environmental changes.

Conversion of croplands to shrublands does not improve soil organic carbon and nitrogen but reduces soil phosphorus in a temperate grassland of northern China

Understanding changes in soil organic carbon and nutrient contents through converting grasslands to croplands and croplands to shrublands is critically important for grassland management. To investigate the impact of land-use changes on soil properties, we chose five sites within 60 km of the temperate grassland in Inner Mongolia as replicates. At each site, soil and vegetation characteristics of three land-use types, including natural grasslands, croplands, and shrublands (shrublands were converted from croplands), were separately investigated. We found the highest aboveground biomass in shrublands and the highest root biomass in grasslands among the three land-use types. We also found that soil bulk density increased, but soil organic carbon (OC), total nitrogen (TN) and total phosphorus (TP) contents decreased significantly in the cropland compared to the natural grassland. Compared with the long-term planted cropland, the 17-year-old shrub plantation did not significantly change soil organic carbon and nitrogen contents and storages, while it significantly reduced the soil phosphorus content and storage. Moreover, soil C:P ratio was the highest in the shrubland but the lowest in the cropland at 0–10 cm soil layer, while soil C:N and N:P ratios remained relatively stable in different land-use types within 0–50 cm soil profile. These findings demonstrate that the current shrub plantation and utilization mode are still not effective in restoring soil organic carbon and nutrients in the temperate grassland in Inner Mongolia. Further management improvements, such as decreasing mowing utilization and sowing herbage with developed roots in shrublands, are needed to accelerate the restoration.

Variation in microbial CAZyme families across degradation severity in a steppe grassland in northern China

Little is known about the effects of grassland degradation on the carbohydrate-active enzyme (CAZYme) genes responsible for C cycling. Here we used a metagenomic approach to reveal variation in abundance and composition of CAZyme genes in grassland experiencing a range of degradation severity (i.e., non-, light, moderately, and severely degraded) in two soil layers (0–10 cm, 10–20 cm) in a steppe grassland in northern China. We observed a higher CAZyme abundance in severely degraded grassland compared with the other three degradation severities. Glycoside hydrolase (GH) and glycosyltransferase (GT) were identified as the most abundant gene families. The Mantel test and variation partitioning suggested an interactive effect of degradation severity and soil depth with respect to CAZyme gene composition. Structural equation modeling indicated that total soil carbon, microbial biomass carbon and organic carbon were the three soil characteristics most important to CAZyme abundance, which suggests an interaction between degradation and soil carbon fractions in determining CAZyme gene composition. Both above- and below-ground factors linked to soil organic matter play a central role in determining the abundance of CAZyme gene families.

Corrigendum: The roles for branch shelters and sheep manure to accelerate the restoration of degraded grasslands in northern China

CORRECTION article Front. Environ. Sci., 03 February 2023Sec. Soil Processes Volume 11 - 2023 | https://doi.org/10.3389/fenvs.2023.1138449

Comparing Machine Learning Algorithms for Pixel/Object-Based Classifications of Semi-Arid Grassland in Northern China Using Multisource Medium Resolution Imageries

Knowledge of grassland classification in a timely and accurate manner is essential for grassland resource management and utilization. Although remote sensing imagery analysis technology is widely applied for land cover classification, few studies have systematically compared the performance of commonly used methods on semi-arid native grasslands in northern China. This renders the grassland classification work in this region devoid of applicable technical references. In this study, the central Xilingol (China) was selected as the study area, and the performances of four widely used machine learning algorithms for mapping semi-arid grassland under pixel-based and object-based classification methods were compared: random forest (RF), support vector machine (SVM), k-nearest neighbor (KNN), and naive Bayes (NB). The features were composed of the Landsat OLI multispectral data, spectral indices, Sentinel SAR C bands, topographic, position (coordinates), geometric, and grey-level co-occurrence matrix (GLCM) texture variables. The findings demonstrated that (1) the object-based methods depicted a more realistic land cover distribution and had greater accuracy than the pixel-based methods; (2) in the pixel-based classification, RF performed the best, with OA and Kappa values of 96.32% and 0.95, respectively. In object-based classification, RF and SVM presented no statistically different predictions, with OA and Kappa exceeding 97.5% and 0.97, respectively, and both performed significantly better than other algorithms. (3) In pixel-based classification, multispectral bands, spectral indices, and geographic features significantly distinguished grassland, whereas, in object-based classification, multispectral bands, spectral indices, elevation, and position features were more prominent. Despite the fact that Sentinel 1 SAR variables were chosen as an effective variable in object-based classification, they made no significant contribution to the grassland distinction.

Increasing precipitation weakened the negative effects of simulated warming on soil microbial community composition in a semi-arid sandy grassland.

Soil microbial diversity, composition, and function are sensitive to global change factors. It has been predicted that the temperature and precipitation will increase in northern China. Although many studies have been carried out to reveal how global change factors affect soil microbial biomass and composition in terrestrial ecosystems, it is still unexplored how soil microbial diversity and composition, especially in microbial functional genes, respond to increasing precipitation and warming in a semiarid grassland of northern China. A field experiment was established to simulate warming and increasing precipitation in a temperate semiarid grassland of the Horqin region. Soil bacterial (16S) and fungal (ITS1) diversity, composition, and functional genes were analyzed after two growing seasons. The result showed that warming exerted negative effects on soil microbial diversity, composition, and predicted functional genes associated with carbon and nitrogen cycles. Increasing precipitation did not change soil microbial diversity, but it weakened the negative effects of simulated warming on soil microbial diversity. Bacterial and fungal diversities respond consistently to the global change scenario in semiarid sandy grassland, but the reasons were different for bacteria and fungi. The co-occurrence of warming and increasing precipitation will alleviate the negative effects of global change on biodiversity loss and ecosystem degradation under a predicted climate change scenario in a semiarid grassland. Our results provide evidence that soil microbial diversity, composition, and function changed under climate change conditions, and it will improve the predictive models of the ecological changes of temperate grassland in future climate change scenarios.

Mechanisms of dust emissions from lakes during different drying stages in a semi-arid grassland in northern China

Semi-arid playas are important to grassland ecosystem species as an important source of global dust emissions. However, there is a lack of data on dust emissions during the different drying stages of grassland playas. In this study, we initially conducted the field experiments on two types of surfaces (intermittently dried and permanently dried) in playas located in semi-arid regions in northern China, and we measured dust emissions at five wind speeds in spring when wind erosion was frequent. The results showed that the intermittently dried surface was more prone to wind erosion, which was primarily due to the formation of a loose and fragile salt crust on the surface. In addition, the proportion of salt in the dust was higher than that for the permanently dried surfaces. Nevertheless, the total horizontal dust flux (1.13–2.3 g/cm2·min) from the intermittently dried surface was only 5%–15% that of the permanently dried surface (7.47–42.86 g/cm2·min). The dust content varied linearly with the height of the intermittently dried surface, and varied exponentially with the height of the permanently dried surface. The particles collected on the intermittently dried surface were larger (<63 μm) than those collected on the permanently dried surface (<10 μm), and the unit mass concentration of each ion (mainly Na+, Cl−, and SO42−) in the salt dust was also higher for the intermittently dried surface than for the permanently dried surface. Although salt dust was continuously released from the intermittently dried surface, the total amount released each time was limited. These results indicate that to attenuate the damage of salt dust storms, priority should be given to protecting permanently dried surfaces and reducing the supply of salt dust particles at the surface.

The roles for branch shelters and sheep manure to accelerate the restoration of degraded grasslands in northern China

New strategies are desperately needed for restoring the millions of hectares of degraded grasslands in arid and semiarid areas of northern China. This study evaluated using different combinations of manure amendments and shrub branch shelters for their impacts on soil moisture, nutrient availability, and plant growth over two growing seasons in a degraded grassland in Ningxia, China. A two-factor experiment was conducted, with three concentrations of 1.2 g m−2, 442 g m−2, and 884 g m−2 native Tan sheep manure as the main plots. Cut caragana (Caragana intermedia) branches were used to create branch shelters covering 0%, 20%, 40%, and 60% of ground area, and these acted as sub-main plots. Soil water storage, soil temperature, manure decomposition, branch decomposition, soil nutrients, and plant growth were monitored for 2 years. Results indicated that soil water storage was significantly increased, and soil temperature decreased, under the 40% and 60% branch shelters. Decomposition rate of manure and shrub branches also increased with increasing soil water availability associated with the higher branch sheltering effects, although soil carbon and nitrogen concentrations were primarily driven by the decomposing manure. The combination of high levels of shrub branch shelter and manure application significantly enhanced plant production, although the bulk of the biomass was concentrated in one species, Artemisia scoparia. In conclusion, our study successfully demonstrated feasible and inexpensive solution for the restoration of degraded grasslands, which takes advantage of resources associated with overgrazing Tan sheep and Caragana shrub encroachment in arid and semiarid areas.

Plant compensatory growth and optimal grazing intensity of grasslands in northern China: A meta-analysis of grazing experiments

补偿性生长是草地植物对动物采食的一种适应策略，合理的放牧强度能够促进植物的补偿性生长，有利于草地生产力和稳定性的维持，而长期过度放牧则导致草地退化. 因此，确定合理的放牧强度是科学配置草地生产-生态功能，实现草牧业可持续发展的基础. 本文基于各类放牧实验已发表的118篇研究文献，将放牧家畜的采食率（地上生物量移除量，%）作为放牧强度的测度指标，对我国北方5种主要草地类型的植物补偿生长特征和其合理放牧强度进行了整合分析，并结合气候、土壤及植物群落地下生物量和多样性等数据，厘清了影响植物补偿生长的关键生物和非生物因子. 结果表明，我国北方草地植物总体处于欠补偿生长状态，且植物地上部分的补偿性生长主要以牺牲其地下生物量为代价. 其中，高寒草甸、草甸草原和荒漠草原植物均表现欠补偿生长，高寒草原和典型草原植物表现等补偿生长. 在区域尺度上，补偿性生长的绝对值随年降水量和植物物种丰富度的增加而增加. 满足植物群落地上生物量实现等补偿或超补偿，且对地下生物量不产生负效应，各类草地的合理利用强度为：高寒草甸50%、草甸草原48%、典型草原40%、高寒草原37%、荒漠草原31%. 本研究对指导我国北方草地保护与合理利用，以及退化草地恢复具有重要的理论和实践意义.