Grassland Ecosystem Function Research Articles

Cessation of grazing stabilizes productivity through effects on species asynchrony and stability of shrub/semi-shrub plants in arid grasslands

Grasslands are globally abundant and important ecosystems, supporting considerable biodiversity and the livelihoods of herders. However, many grasslands have become degraded through overgrazing. Cessation of grazing can have significant effects on grassland biodiversity and ecosystem functioning, yet, to date, there is no consensus about how grazing cessation affects temporal stability of plant community productivity or the underlying mechanisms driving effects. In this study, we evaluated the effects of grazing cessation on the temporal stability of annual net primary productivity (ANPP) in the plant communities, using a 15-year field experiment conducted in an Inner Mongolian desert steppe landscape. Plant diversity, species asynchrony and the temporal stability of ANPP of functional groups were analyzed to explore the driving mechanisms of temporal stability of plant community ANPP during periods without grazing. The results showed that plant ANPP and its temporal stability of whole community, shrubs/semi-shrubs and perennial forbs were greater in areas when grazing had ceased compared with areas under continuous grazing. Grazing cessation increased both species asynchrony and species richness at the community level. Structural equation modelling (SEM) was used to better understand the mechanisms behind the result and showed that grazing cessation increased temporal stability of community ANPP by increasing species asynchrony and the temporal stability of shrubs/semi-shrubs ANPP. Temporal stability of whole community ANPP were not related to species richness. Our study also found that the effects of grazing cessation on temporal stability of community ANPP was largest during the initial five years, while the latter ten years of grazing cessation had few additional effects on temporal stability of community ANPP. Together, our results suggest that species asynchrony and the temporal stability of shrubs/semi-shrubs ANPP may be the key drivers affecting temporal stability of community ANPP during grazing cessation, and short-term grazing cessation may be more impactful than medium- or longer term grazing cessation.

Early Evidence That Soil Dryness Causes Widespread Decline in Grassland Productivity in China

The burning of fossil fuels by humans emits large amounts of CO2 into the atmosphere and strongly affects the Earth’s carbon balance, with grassland ecosystems changing from weak carbon sinks that were previously close to equilibrium to core carbon sinks. Chinese grasslands are located in typical arid–semi-arid and semi-arid climatic regions, and drought events in the soil and atmosphere can have strong and irreversible consequences on the function and structure of Chinese grassland ecosystems. Based on this, we investigated the response of the gross primary production (GPP) of Chinese grasslands to land–atmosphere moisture constraints, using GPP data simulated through four terrestrial ecosystem models and introduced copula functions and Bayesian equations. The main results were as follows: (1) Soil moisture trends were not significant, and changes were dominated by interannual variability. The detrended warm-season SM correlated with GPP at 0.48 and 0.63 for the historical and future periods, respectively; thus, soil moisture is the critical water stress that regulates interannual variability in Chinese grassland GPP. (2) The positive correlation between shallow SM (0–50 cm) and GPP was higher (r = 0.62). Shallow-soil moisture is the main soil layer that constrains GPP, and the soil moisture decrease in shallow layers is much more likely to cause GPP decline in Chinese grasslands than that in deep-soil water. (3) The probability of GPP decline in Chinese grasslands caused by drought in shallow soils of 0–20 and 20–50 cm is 32.49% and 27.64%, respectively, which is much higher than the probability of GPP decline in deeper soils. In particular, soil drought was more detrimental to grassland GPP in Xinjiang and the Loess Plateau. (4) The probability of soil drought causing GPP decline was higher than that of atmospheric drought during the historical period (1.78–8.19%), but the probability of an atmospheric drought-induced GPP deficit increases significantly in the future and becomes a key factor inhibiting GPP accumulation in some regions (e.g., the Loess Plateau). Our study highlighted the response of grassland ecosystems after the occurrence of soil drought, especially for the shallow-soil-water indicator, which provides important theoretical references for grassland drought disaster emergency prevention and policy formulation.

Multifunctionality of temperate alley-cropping agroforestry outperforms open cropland and grassland

Intensively managed open croplands are highly productive but often have deleterious environmental impacts. Temperate agroforestry potentially improves ecosystem functions, although comprehensive analysis is lacking. Here, we measured primary data on 47 indicators of seven ecosystem functions in croplands and 16 indicators of four ecosystem functions in grasslands to assess how alley-cropping agroforestry performs compared to open cropland and grassland. Carbon sequestration, habitat for soil biological activity, and wind erosion resistance improved for cropland agroforestry (P ≤ 0.03) whereas only carbon sequestration improved for grassland agroforestry (P < 0.01). In cropland agroforestry, soil nutrient cycling, soil greenhouse gas abatement, and water regulation did not improve, due to customary high fertilization rates. Alley-cropping agroforestry increased multifunctionality, compared to open croplands. To ameliorate the environmental benefits of agroforestry, more efficient use of nutrients is required. Financial incentives should focus on conversion of open croplands to alley-cropping agroforestry and incorporate fertilizer management.

Artificial reseeding improves multiple ecosystem functions in an alpine sandy meadow of the eastern Tibetan Plateau

AbstractDesertification in alpine grasslands is exacerbated by rapid climate change and intensive anthropogenic activity, which will substantially threaten the structure and function of alpine grassland ecosystems. Artificial reseeding was a widely used strategy for the restoration of alpine sandy grasslands. However, it is still unclear whether reseeding restoration can improve multiple ecosystem functions of sandy meadows. To narrow these knowledge gaps, we evaluated the changes in plant communities, soil conditions, and ecosystem multifunctionality (EMF) across native meadow, sandy meadow, and restored meadow on the eastern Tibetan Plateau, and further identified the links between individual and multiple ecosystem functions. Artificial reseeding had contributed to the promotion of plant diversity, productivity, soil fertility, and soil carbon and nitrogen sequestrations. However, the recovery levels of plant diversity, productivity, and soil fertility in the restored meadow were still far lower than that in the native meadow. The results revealed that the EMF index of the restored meadow increased greatly compared with the sandy meadow, but it did not recover to that of the native meadow level. In addition, short‐term reseeding improved the aboveground EMF index more than the belowground EMF index. The EMF indexes and most individual ecosystem functions showed positive correlations with plant diversity and productivity. These findings indicated an important role of artificial reseeding in the restoration of ecosystem functions in the alpine sandy meadow, and it had critical implications for the regional ecological security and sustainable development of alpine grasslands.

Effects of Grazing, Extreme Drought, Extreme Rainfall and Nitrogen Addition on Vegetation Characteristics and Productivity of Semiarid Grassland.

Grassland use patterns, water and nutrients are the main determinants of ecosystem structure and function in semiarid grasslands. However, few studies have reported how the interactive effects of rainfall changes and nitrogen deposition influence the recovery of semiarid grasslands degraded by grazing. In this study, a simulated grazing, increasing and decreasing rainfall, nitrogen deposition test platform was constructed, and the regulation mechanism of vegetation characteristics and productivity were studied. We found that grazing decreased plant community height (CWMheight) and litter and increased plant density. Increasing rainfall by 60% from May to August (+60%) increased CWMheight; decreasing rainfall by 60% from May to August (-60%) and by 100% from May to June (-60 d) decreased CWMheight and coverage; -60 d, +60% and increasing rainfall by 100% from May to June (+60 d) increased plant density; -60% increased the Simpson dominance index (D index) but decreased the Shannon-Wiener diversity index (H index); -60 d decreased the aboveground biomass (ABG), and -60% increased the underground biomass (BGB) in the 10-60 cm layer. Nitrogen addition decreased species richness and the D index and increased the H index and AGB. Rainfall and soil nitrogen directly affect AGB; grazing and rainfall can also indirectly affect AGB by inducing changes in CWMheight; grazing indirectly affects BGB by affecting plant density and soil nitrogen. The results of this study showed that in the semiarid grassland of Inner Mongolia, grazing in the nongrowing season and grazing prohibition in the growing season can promote grassland recovery, continuous drought in the early growing season will have dramatic impacts on productivity, nitrogen addition has a certain impact on the species composition of vegetation, and the impact on productivity will not appear in the short term.

日尺度下水热因子变化对青藏高原高寒草原生产力的影响特征

PDF HTML阅读 XML下载 导出引用 引用提醒 日尺度下水热因子变化对青藏高原高寒草原生产力的影响特征 DOI: 10.5846/stxb202112103509 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(41701606,U21A2021);中央高校基本科研业务费(2452020009);陕西省自然科学基础研究计划(2021JM-093) Effects of daily variation of hydro-thermal factors on alpine grassland productivity on the Qinghai-Tibet Plateau Author: Affiliation: Fund Project: National Natural Science Foundation of China (41701606、U21A2021)；the Fundamental Research Funds for the Central Universities (2452020009)、Natural Science Basic Research Program of Shaanxi Province(2021JM-093) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:温度和降水变化显著影响高寒生态系统植被生长和系统功能。草地生产力作为草地系统功能强弱的重要体现,对气候变化,特别是温度和降水变化十分敏感。探究高寒草原生产力如何响应气候变化,对预测未来气候变化情景下高寒草地系统功能变化意义重大。前期研究大都从年或季节尺度探究气候变化对草地生产力的影响特征,缺乏更精细时间尺度的关联分析。本研究基于 1997-2020 年青藏高原高寒草原长期植被观测数据及相应气候资料,应用简单线性回归及偏最小二乘回归法(Partial Least Squares regression, PLS)探究了研究区草地地上净初级生产力对日尺度温度和降水变化响应特征。结果表明:(1)近24 a来研究区年平均气温和降水量分别以0.03℃/a和4.36 mm/a的速率显著升高;(2)近24 a来研究区草地生产力显著升高(增幅为5.24 g m-2 a-1),且与年平均温度和降水量呈显著正相关关系;(3)日尺度分析表明,不同阶段温度和降水变化对草地生产力的影响不同,其中5-8月和9-10月的温度及5-7月和9-11月的降水是影响研究区草地生产力的气候因子关键作用期,尤以生长季温度(5-8月)和降水(5-7月)变化影响更高,这表明生长季气候变化是该高寒草地生产力变化的主要驱动因素。总之,本研究指出近24 a生长季温度和降水量显著增加对高寒草原生产力具有重要促进作用,这意味着青藏高原暖湿化对高寒草原生态系统功能(草地生产力)影响不仅依赖于温度和降水变化的幅度,同时亦与温度和降水变化的方向和是否同步密切相关。 Abstract:Changes in temperature and precipitation significantly affect plant growth and system function in the alpine ecosystem. As an important reflection of grassland system function, grassland productivity is very sensitive to climate change, especially to temperature and precipitation. Therefore, it is significant to explore how grassland productivity responds to climate change for predicting system function in the alpine steppe under the background of future climate change. Previous studies often investigated the effects of climate change on grassland productivity at annual or seasonal scales, but there was a lack of correlation analysis at finer time scales. Based on the long-term productivity records and corresponding climatic data from 1997 to 2020, we used simple linear regression and partial least squares regression to reveal the responses of grassland productivity to temperature and precipitation on a daily scale. The results showed that: (1) the annual mean temperature and precipitation in the study area increased significantly in the past 24 years, with a rate of 0.03 ℃/a and 4.36 mm/a, respectively. (2) Meanwhile, grassland productivity increased significantly, with a rate of 5.24 g m-2 a-1, and had significantly positive responses to annual mean temperature and precipitation variation. (3) The results of the daily analysis showed that the effects of temperature and precipitation during different periods on grassland productivity were different. In specific, the temperature from May to August and September to October and precipitation from May to July and September to November were key periods to explain the impacts of climate change on grassland productivity, especially temperature (May to August) and precipitation (May to July) variations during the growing season had the higher impacts on grassland productivity, suggesting climate change in the growing season was the main driving factor for variation in grassland productivity. Overall, the present study indicated that increasing temperature and precipitation during the growing season in the past 24 years significantly promoted grassland productivity of the alpine steppe. The effects of warm-wet climate on alpine grassland ecosystem function (e.g., grassland productivity) were closely dependent on the magnitude, direction, and synchronization of altered temperature and precipitation. 参考文献 相似文献 引证文献

Photovoltaic panels have altered grassland plant biodiversity and soil microbial diversity.

Human concerns about fossil fuel depletion, energy security and environmental degradation have driven the rapid development of solar photovoltaic (PV) power generation. Most of the photovoltaic power generation plants are concentrated in desert, grassland and arable land, which means the change of land use type. However, there is still a gap in the research of the PV panel layout on grassland plant species diversity and ecological function. In this study, Illumina high-throughput sequencing technology was used to investigate the effects of PV panel arrangement on grassland plant species diversity and soil microbial diversity. In view of the differences in the microclimate at different sites of the PV panels, quadrates were arranged in front edge (FE), beneath the center of each panel (BP), back edge (BE), the uncovered interspace adjacent to each panel (IS) and the undisturbed grassland around the PV panels (Control), respectively. PV panels (especially FE) significantly increased the total aboveground productivity (total AGB) and plant species diversity in grasslands. FE increased precipitation accumulation and plant species diversity directly and indirectly changed the diversity of soil bacterial and fungal communities. PV panels decreased the relative abundance of Actinobacteriota, while increased the relative abundance of Proteobacteria, Acidobacteriota, and Methylomirabilota. EC, Margalef' s richness and total AGB were the main factors affecting the composition of bacterial communities, while alkaline hydrolysis nitrogen (AN) and available phosphorus (AP) were the main factors affecting the composition of fungal communities. In conclusion, the arrangement of PV panels increased the plant species diversity and soil microorganisms in grassland. This study provides important information for further understanding the impact of PV panels on grassland ecosystem function and is of great significance for maintaining grassland ecosystem function.

Effects of decadal nitrogen and phosphorus fertilization on microbial taxonomic and functional attributes associated with soil organic carbon decomposition and concentration in an alpine meadow

Microorganisms drive many important soil processes and ecosystem functioning; however, the soil microbial community can respond to environmental change, which can alter decomposition and storage of soil organic carbon (SOC). We assessed soil microbial taxonomic and functional attributes linked to SOC decomposition and concentration based on a grassland experiment fertilized with nitrogen (N) and phosphorus (P). There were divergent responses at both the taxonomic and functional level to fertilization, with a greater quantitative response in terms of the taxonomic attributes of bacteria and fungi than the abundance of SOC degradation genes. There was a negative correlation between SOC concentration and the abundance of SOC degradation genes. This indicated that N and P fertilization had the potential to stimulate SOC decomposition through modification of the soil microbial community, particularly by increasing the abundance of SOC degradation genes. Redundancy and variation partitioning analyses, as well as structural equation models revealed that soil total P was a pivotal factor shaping the microbial community both for taxonomic and functional gene attributes in the alpine meadow. The abundance of SOC degrading genes had stronger effects on SOC concentrations than did taxonomic attributes. Quantification of the abundance of SOC degradation genes can provide more direct and effective understanding of SOC decomposition processes and prediction of shifts in soil function as organic C pool in grasslands than a focus on the taxonomy of microbial communities. Given the important role of microbial community in regulating SOC decomposition and lower SOC concentrations under N and P fertilization, we recommend that the alpine meadow should be protected from mineral fertilizers, particularly P alone fertilization, to sustain high grassland ecosystem function as SOC sink in this region.

Grassland Degradation Has Stronger Effects on Soil Fungal Community Than Bacterial Community across the Semi-Arid Region of Northern China.

Soil microbes play crucial roles in grassland ecosystem functions, such as soil carbon (C) pool and nutrient cycle. Soil microbes in grasslands are susceptible to the degradation mediated by climate change and anthropogenic disturbance. However, research on how the degradation influences the diversity and community structure of different soil microbial taxa is relatively scarce. We conducted a large-scale field survey to describe the effects of four degradation levels (PD: potential degradation, LD: light degradation, MD: moderate degradation, and SD: severe degradation) on soil bacterial and fungal community in the semi-arid grasslands of northern China. We found that soil moisture, nutrients, and clay content decreased, but soil sand content increased along the increasing degradation gradient. However, the degradation had no effects on soil pH and the C:N ratio. Grassland degradation had non-significant effect on soil bacterial diversity, but it significantly affected soil bacterial community structure. The degradation decreased soil fungal diversity and had a relatively larger influence on the community structure of soil fungi than that of bacteria. The community composition and structure of soil fungi were mainly affected by soil nutrients and texture, while those of soil bacteria were mainly affected by soil pH. These results indicate that changes in soil properties induced by grassland degradation mainly drive the variation in the soil fungal community and have less effect on the soil bacterial community. This study reveals the sensitivity of soil fungal community to grassland degradation, highlighting the priority of soil fungal community for the management and restoration of degraded grasslands.

Resilience of ecosystem service delivery in grasslands in response to single and compound extreme weather events

Extreme weather events are increasing in frequency and magnitude with profound effects on ecosystem functioning. Further, there is now a greater likelihood that multiple extreme events are occurring within a single year. Here we investigated the effect of a single drought, flood or compound (flood + drought) extreme event on temperate grassland ecosystem processes in a field experiment. To assess system resistance and resilience, we studied changes in a wide range of above- and below-ground indicators (plant diversity and productivity, greenhouse gas emissions, soil chemical, physical and biological metrics) during the 8 week stress events and then for 2 years post-stress. We hypothesized that agricultural grasslands would have different degrees of resistance and resilience to flood and drought stress. We also investigated two alternative hypotheses that the combined flood + drought treatment would either, (A) promote ecosystem resilience through more rapid recovery of soil moisture conditions or (B) exacerbate the impact of the single flood or drought event. Our results showed that flooding had a much greater effect than drought on ecosystem processes and that the grassland was more resistant and resilient to drought than to flood. The immediate impact of flooding on all indicators was negative, especially for those related to production, and climate and water regulation. Flooding stress caused pronounced and persistent shifts in soil microbial and plant communities with large implications for nutrient cycling and long-term ecosystem function. The compound flood + drought treatment failed to show a more severe impact than the single extreme events. Rather, there was an indication of quicker recovery of soil and microbial parameters suggesting greater resilience in line with hypothesis (A). This study clearly reveals that contrasting extreme weather events differentially affect grassland ecosystem function but that concurrent events of a contrasting nature may promote ecosystem resilience to future stress.

Effects of grazing on soil aggregate composition and stability in Stipa breviflora desert steppe

Grazing, one of the main grassland utilization modes, has notable impacts on grassland ecosystem structure and functions. However, the effects of long-term grazing on soil aggregate composition and stability are poorly understood. Based on a long-term grazing experiment platform in Inner Mongolia Stipa breviflora desert steppe established in 2004, with treatements of no grazing (control), light, moderate, and heavy grazing intensities, we studied the changes of soil aggregate composition and stability under different grazing intensities. With the measurement of relevant soil physical and chemical characteristics, we explored the main factors that affecting the stability of soil aggregates. The results showed that grazing significantly altered soil aggregate composition. Compared with control, the content of large aggregates (0.25-2 mm) was unchanged in light grazing but significantly decreased in treatments with moderate and heavy grazing intensities. Heavy grazing significantly decreased the content of small aggregates (0.053-0.25 mm), while light and moderate grazing significantly increased that of microaggregates (<0.053 mm). Soil aggregate stability was maintained at a high level under light grazing, but significantly decreased under moderate and heavy grazing treatments. Soil aggregate stability was positively correlated with macroaggregate content but negatively correlated with microaggregate content. Soil pH, bulk density, organic carbon and other physicochemical indices jointly contributed to the changes of soil aggregate composition and hence affect soil aggregate stability. In conclusion, our results showed that appropriate grazing could maintain high level of soil aggregate stability in desert steppe.

Bison movements change with weather: Implications for their continued conservation in the Anthropocene.

Animal movement patterns are affected by complex interactions between biotic and abiotic landscape conditions, and these patterns are being altered by weather variability associated with a changing climate. Some animals, like the American plains bison (Bison bison L.; hereafter, plains bison), are considered keystone species, thus their response to weather variability may alter ecosystem structure and biodiversity patterns. Many movement studies of plains bison and other ungulates have focused on point-pattern analyses (e.g., resource-selection) that have provided information about where these animals move, but information about when or why these animals move is limited. For example, information surrounding the influence of weather on plains bison movement in response to weather is limited but has important implications for their conservation in a changing climate. To explore how movement distance is affected by weather patterns and drought, we utilized 12-min GPS data from two of the largest plains bison herds in North America to model their response to weather and drought parameters using generalized additive mixed models. Distance moved was best predicted by air temperature, wind speed, and rainfall. However, air temperature best explained the variation in distance moved compared to any other single parameter we measured, predicting a 48% decrease in movement rates above 28°C. Moreover, severe drought (as indicated by 25-cm depth soil moisture) better predicted movement distance than moderate drought. The strong influence of weather and drought on plains bison movements observed in our study suggest that shifting climate and weather will likely affect plains bison movement patterns, further complicating conservation efforts for this wide-ranging keystone species. Moreover, changes in plains bison movement patterns may have cascading effects for grassland ecosystem structure, function, and biodiversity. Plains bison and grassland conservation efforts need to be proactive and adaptive when considering the implications of a changing climate on bison movement patterns.

Biodiversity and soil pH regulate the recovery of ecosystem multifunctionality during secondary succession of abandoned croplands in northern China

The ‘Grain-for-Green’ program in China provides a valuable opportunity to investigate whether spontaneous restoration can reverse the deterioration of grassland ecosystem functions. Previous studies have focused on individual ecosystem functions, but the response of and mechanisms driving variation in ecosystem multifunctionality (EMF) during restoration are poorly understood. Here, we quantified EMF using productivity, nutrient cycling, and water regulation functions along abandoned croplands in a recovery chronosequence (5, 15 and 20 years) and in natural grasslands in the desert steppe and typical steppe. We also analyzed the effects of plant and microbial diversity and an abiotic factor (soil pH) on EMF. Our results showed that EMF increased gradually concomitant with recovery time, shifting toward EMF values comparable to those in natural grasslands in both desert and typical steppe. Similar results were found for the productivity function, the water regulation function, and soil organic carbon. However, even after 20 years of restoration, EMF did not reach the levels observed in natural grasslands. Structural equation modeling showed that the driving mechanisms of EMF differed between the two steppe types. Specifically, in the desert steppe, plant diversity, especially the diversity of perennial graminoids and perennial herbs, had a positive effect on EMF, but in the typical steppe, soil bacterial diversity had a negative effect, while soil pH had a positive effect on EMF. Our results demonstrated that spontaneous grassland restoration effectively enhanced EMF, and emphasized the importance of biodiversity and soil pH in regulating EMF during secondary succession. This work provides important insights for grassland ecosystem management in arid and semi-arid regions.

Relationship between Biomass and Biodiversity of Degraded Grassland in the Sanjiangyuan Region of Qinghai–Tibet Plateau

Understanding the mechanisms of diversity–productivity relationships is a central question in community ecology. Grazing is the main driving force affecting biodiversity, function, and stability of grassland ecosystems, and thus should play an important role in mediating diversity-productivity relationships. In this study, we examined the effect of grazing intensity on both aboveground biomass and biodiversity and explored the relationship between them in alpine meadow ecosystems in Sanjiangyuan, which is the source of the Yangtze, Yellow, and Lancang rivers. The results showed that the aboveground biomass and species richness decreased significantly due to multi-state succession in alpine meadows caused by long-term grazing, while the Shannon–Wiener index and Pielou evenness index decreased and then increased with increasing grazing intensity. The relationship between the aboveground biomass and biodiversity was U-shaped. Our results highlighted the opposite pattern of the diversity–productivity relationship under low and medium grazing intensity versus an extremely high grazing intensity; evenness contributed largely to this pattern. This study provided a new perspective on grassland management and the relationship between productivity and biodiversity. Attention should be paid to rational grazing to restore biodiversity and ecosystem functions and services in alpine meadows.

Root systems reserve under humid conditions of floodplain meadows of the Ob River in the subzone of the southern taiga

The results of the study of the underground phytomass of the floodplain meadow communities in the Middle Ob obtained from three permanent sample plots in the area of the Kaibasovo research station of Tomsk University (Kri-vosheinsky district of the Tomsk region) are presented. The functioning and productivity of grassland ecosystems should be carefully studied, especially in the light of ongoing climate change, as they are actively involved in the carbon cycle. However, the belowground phytomass is given much less attention in the literature than the aboveground part, despite the fact that they are equally important for the study of the cycle. The study of vegetation cover in order to analyze the biological cycle of flood-plain ecosystems, the production and destruction of plant matter in this area was practically not carried out. The goal was to assess the structure and stock of root phytomass in the meadows of the Ob floodplain. In the course of the work, the hydro-climatic conditions of the growing season of the current and previous years were characterized in order to assess their impact on root development. The reserves of underground organs in the 0-20 cm soil layer were determined, the limits of fluctuations of the total reserves of roots in the 0-20 cm layer between the sampling periods in June and August were established.&#x0D; Key words. Belowground biomass, flood, floodplain meadows, productivity, roots, Western Siberia.

Drought‐driven shifts in relationships between plant biodiversity and productivity in temperate steppes

Abstract Drought events induced by global climate change strongly modify ecosystem structure and function in grasslands. Higher plant biodiversity can enhance ecosystem resistance to drought; however, the potential effects of drought on the relationships between above‐ground productivity (ANPP) and biodiversity along a natural aridity gradient remain poorly understood. Here, we studied the effects of experimental drought on plant community structure and ANPP during the two different dry years (2015 and 2017) spanning three temperate steppe sites with low‐, medium‐ and high‐aridity levels. We also examined the effects of drought and aridity on the associations of plant species (richness and abundance), functional (community‐weighted trait means and functional dispersion) and phylogenetic diversity (evolutionary lineages) with ANPP. A structural equation modelling (SEM) was used to elucidate how the drought affected ANPP by altering biodiversity attributes. We found that experimental drought shaped the biodiversity–ANPP relationships, and the biodiversity–ANPP relationships differed among three sites. At the low‐aridity site, ANPP was correlated with plant functional traits, whereas ANPP was correlated with functional dispersion, species and phylogenetic diversity at the medium‐aridity site. At the high‐aridity site, ANPP was correlated with species richness, functional traits and phylogenetic diversity. Compared with 2015, natural drought in 2017 strengthened the associations of species diversity, functional dispersion, leaf dry matter content and leaf nitrogen content with ANPP across three sites. SEM further showed that both experimental and natural drought directly decreased ANPP and indirectly decreased ANPP by reducing community‐weighted mean of plant height. Synthesis. These results suggest that the aridity increase or drought occurrence is likely to induce the shifts in the associations of ANPP with species and functional diversity, highlighting the important role of water availability or precipitation conditions in regulating the biodiversity–ANPP relationships in temperate steppes. Overall, functional traits related to plant size play a crucial role in modulating the response of productivity to drought across three steppe sites. Thus, to buffer the negative effects of drought on steppe ANPP should pay attention to protect the species with large plant size. Read the free Plain Language Summary for this article on the Journal blog.

Grassland degradation-induced declines in soil fungal complexity reduce fungal community stability and ecosystem multifunctionality

Soil microorganisms are major regulators of ecosystem functioning and are under threat from human-induced disturbances. Among these threats is grassland degradation, which is estimated to affect 49% of the grassland area worldwide, threatening biodiversity and ecosystem functioning. Yet, we currently lack an understanding of how grassland degradation influences belowground microbial communities, their stability, and functioning, and how effective restoration efforts are for the recovery of these important belowground properties. Here, we assessed soil fungal network complexity and a suite of ecosystem functions along a well-characterised gradient of grassland degradation and restoration on the Qinghai-Tibetan Plateau, and conducted an accompanying microcosm experiment designed to test the effects of complexity on stability in soil fungal communities. We found that with increasing levels of grassland degradation, soil fungal communities became less complex and were less compositionally stable when confronted with drought under laboratory conditions. Moreover, this degradation-induced reduction in fungal community complexity was associated with lower ecosystem multifunctionality. However, fungal communities and ecosystem multifunctionality failed to recover even after ten years of grassland restoration. Our results indicate that degradation-induced simplification of fungal communities can potentially impair fungal community stability and ecosystem multifunctionality, thereby highlighting the need to protect and restore healthy grasslands with complex belowground microbial communities.

Intensification of disturbance destabilizes productivity through effects on dominant species

• Both intensification and cessation of disturbance destabilized plant productivity. • Community stability was mainly driven by the stability of dominant species. • Maintaining disturbance may be an appropriate strategy for community stability. Disturbances, including anthropogenic disturbances, are integral to the maintenance of grassland ecosystems. Most research on anthropogenic disturbances focuses on the effects of intensification, yet cessation of disturbance can have equally important effects on grassland biodiversity and ecosystem functioning. Natural disturbances have largely been replaced by anthropogenic disturbance, which has pronounced effects on community function and structure in grassland ecosystems. It is still unclear how changing disturbance intensity affects community stability and its mechanisms. We examined the temporal stability of above-ground net primary productivity (ANPP) in a seven-year field mowing experiment which included normal disturbance (control, mowing annually at 5 cm stubble height), increasing disturbance (mowing annually at 2 cm stubble height) and ceasing disturbance (no mowing) in a typical steppe in Inner Mongolia. Overall, ceasing disturbance increased ANPP of whole community but increasing disturbance had no significant effect on community ANPP, which was driven by ANPP of dominant species; and species richness and asynchrony were independent of changing disturbance. Despite having no effect on species richness, both intensification and cessation of disturbance destabilized plant community productivity, primarily through effects on the stability of the dominant species. This highlights the importance of dominant species in driving community dynamics. Maintaining disturbance intensity is an appropriate strategy to maintain hay production and community stability in typical steppe in Inner Mongolia, and may be beneficial to the development of sustainable utilization of grassland and may ensure the income of resident population.

Shrub encroachment drives different responses of soil respiration to increased precipitation and N enrichment

In the context of global change, changes in precipitation patterns and increases in atmospheric nitrogen (N) deposition have important impacts on grassland ecosystem processes and functions, such as soil respiration. However, most studies on the effects of increased precipitation and N enrichment on soil respiration have focused on pure grassland vegetation types (such as typical steppe), but less on grassland at different stages of shrub encroachment. Here, we examined the effects of increased precipitation and N enrichment on soil respiration and its components (heterotrophic and autotrophic respiration) in different stages of shrub-encroached steppe (i.e., no shrub invasion, light, moderate and severe encroachment) based on water and N addition experiments. Our results showed that increased precipitation greatly promoted soil respiration in typical steppe, lightly and moderately shrub-encroached steppe, but had no significant effects in severely encroached steppe; particularly, soil respiration in a wet year (2021) was significantly higher than that in a dry year (2020). However, N addition had no significant effect on soil respiration across the four stages of shrub encroachment, mainly due to the severe soil water limitation. In general, shrub encroachment significantly reduced soil respiration in Inner Mongolia steppe, mainly by increasing soil temperature, but decreasing soil moisture, microbial biomass and root biomass. We found that the driving factors of soil respiration varied with the development of shrub encroachment, especially the biological factors gradually shifted from aboveground plant community to underground microbial community. These findings have important implications for assessing carbon emissions from arid and semi-arid grasslands under global change. Considering that the effects of increased precipitation and N deposition on shrub-encroached steppe (especially severely encroached steppe) were different from those of typical steppe, the stage of shrub encroachment should be fully considered when constructing carbon cycle models to accurately evaluate the carbon emissions of degraded grassland.

A Mixed Model for Assessing the Effect of Numerous Plant Species Interactions on Grassland Biodiversity and Ecosystem Function Relationships

In grassland ecosystems, it is well known that increasing plant species diversity can improve ecosystem functions (i.e., ecosystem responses), for example, by increasing productivity and reducing weed invasion. Diversity-Interactions models use species proportions and their interactions as predictors in a regression framework to assess biodiversity and ecosystem function relationships. However, it can be difficult to model numerous interactions if there are many species, and interactions may be temporally variable or dependent on spatial planting patterns. We developed a new Diversity-Interactions mixed model for jointly assessing many species interactions and within-plot species planting pattern over multiple years. We model pairwise interactions using a small number of fixed parameters that incorporate spatial effects and supplement this by including all pairwise interaction variables as random effects, each constrained to have the same variance within each year. The random effects are indexed by pairs of species within plots rather than a plot-level factor as is typical in mixed models, and capture remaining variation due to pairwise species interactions parsimoniously. We apply our novel methodology to three years of weed invasion data from a 16-species grassland experiment that manipulated plant species diversity and spatial planting pattern and test its statistical properties in a simulation study.Supplementary materials accompanying this paper appear online.