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Ecological succession after disturbance plays a vital role in influencing ecosystem structure and functioning. However, how global change factors regulate ecosystem carbon (C) cycling in successional plant communities remains largely elusive. As part of an 8-year (2012-2019) manipulative experiment, this study was designed to examine the responses of soil respiration and its heterotrophic component to simulated increases in precipitation and atmospheric nitrogen (N) deposition in an old-field grassland undergoing secondary succession. Over the 8-year experimental period, increased precipitation stimulated soil respiration by 11.6%, but did not affect soil heterotrophic respiration. Nitrogen addition increased both soil respiration (5.1%) and heterotrophic respiration (6.2%). Soil respiration and heterotrophic respiration linearly increased with time in the control plots, resulting from changes in soil moisture and shifts of plant community composition from grass-forb codominance to grass dominance in this old-field grassland. Compared to the control, increased precipitation significantly strengthened the temporal increase in soil respiration through stimulating belowground net primary productivity. By contrast, N addition accelerated temporal increases in both soil respiration and its heterotrophic component by driving plant community shifts and thus stimulating soil organic C. Our findings indicate that increases in water and N availabilities may accelerate soil C release during old-field grassland succession and reduce their potential positive impacts on soil C accumulation under future climate change scenarios.

Responses of the terrestrial biosphere to rapidly changing environmental conditions are a major source of uncertainty in climate projections. In an effort to reduce this uncertainty, a wide range of global change experiments have been conducted that mimic future conditions in terrestrial ecosystems, manipulating CO2 , temperature, and nutrient and water availability. Syntheses of results across experiments provide a more general sense of ecosystem responses to global change, and help to discern the influence of background conditions such as climate and vegetation type in determining global change responses. Several independent syntheses of published data have yielded distinct databases for specific objectives. Such parallel, uncoordinated initiatives carry the risk of producing redundant data collection efforts and have led to contrasting outcomes without clarifying the underlying reason for divergence. These problems could be avoided by creating a publicly available, updatable, curated database. Here, we report on a global effort to collect and curate 57,089 treatment responses across 3644 manipulation experiments at 1145 sites, simulating elevated CO2 , warming, nutrient addition, and precipitation changes. In the resulting Manipulation Experiments Synthesis Initiative (MESI) database, effects of experimental global change drivers on carbon and nutrient cycles are included, as well as ancillary data such as background climate, vegetation type, treatment magnitude, duration, and, unique to our database, measured soil properties. Our analysis of the database indicates that most experiments are short term (one or few growing seasons), conducted in the USA, Europe, or China, and that the most abundantly reported variable is aboveground biomass. We provide the most comprehensive multifactor global change database to date, enabling the research community to tackle open research questions, vital to global policymaking. The MESI database, freely accessible at doi.org/10.5281/zenodo.7153253, opens new avenues for model evaluation and synthesis-based understanding of how global change affects terrestrial biomes. We welcome contributions to the database on GitHub. ispartof: GLOBAL CHANGE BIOLOGY vol:29 issue:7 pages:1922-1938 ispartof: location:England status: accepted

Land use and nutrient enrichment can substantially affect biodiversity and ecosystem functioning. However, whether and how the responses of community temporal stability to land use and nutrient enrichment change with time remain poorly understood. As part of a 15-year (2005–2019) field experiment, this study was conducted to explore the effects of mowing, nitrogen (N) and phosphorus (P) additions on community temporal stability in a temperate steppe on the Mongolian Plateau. Over the 15 years, N and P additions decreased community temporal stability by reducing the population stability, especially the shrub and semi-shrub stability. However, mowing increased community temporal stability in the early stage (2005–2009) only. Nitrogen addition suppressed community temporal stability in the early and late (2015–2019) stages, whereas enhanced it in the intermediate stage (2010–2014). Phosphorus addition decreased community temporal stability marginally in the early stage and significantly in the late stage. The fluctuations of N-induced changes in community temporal stability are mainly explained by its diverse effects on species asynchrony and population stability over time. Our findings highlight the important role of plant functional groups and species asynchrony in regulating community temporal stability, suggesting that more long-term studies are needed to accurately forecast ecosystem response patterns in the context of global change.

Anthropogenic nutrient enrichment is known to alter the composition and functioning of plant communities. However, how nutrient enrichment influences multiple dimensions of community- and ecosystem-level stability remains poorly understood. Using data from a nitrogen (N) and phosphorus (P) addition experiment in a temperate semi-arid grassland that experienced a natural drought, we show that N enrichment, not P enrichment, decreased grassland functional and compositional temporal stability, resistance and recovery but increased functional and compositional resilience. Compositional stability and species asynchrony, rather than species diversity, were identified as key determinants of all dimensions of grassland functional stability, except for recovery. Whereas grassland functional recovery was decoupled from compositional recovery, N enrichment altered other dimensions of functional stability primarily through changing their corresponding compositional stability dimensions. Our findings highlight the need to examine ecological stability at the community level for a more mechanistic understanding of ecosystem dynamics in the face of environmental change.

Grazing can affect plant community composition and structure directly by foraging and indirectly by increasing wind erosion and dust storms and subsequently influence ecosystem functioning and ecological services. However, the combined effects of grazing, wind erosion, and dust deposition have not been explored. As part of a 7-year (2010–2016) field manipulative experiment, this study was conducted to examine the impacts of grazing and simulated aeolian processes (wind erosion and dust deposition) on plant community cover and species richness in a temperate steppe on the Mongolian Plateau, China. Grazing decreased total cover by 4.2%, particularly the cover of tall-stature plants (> 20 cm in height), but resulted in 9.1% greater species richness. Wind erosion also reduced total cover by 17.0% primarily via suppressing short-stature plants associated with soil nitrogen loss, but had no effect on species richness. Dust deposition enhanced total cover by 5.7%, but resulted in a 7.3% decrease in species richness by driving some of the short-stature plant species to extinction. Both wind erosion and dust deposition showed additive effects with grazing on vegetation cover and species richness, though no detectable interaction between aeolian processes and grazing could be detected due to our methodological constraints. The changes in gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity under the wind erosion and dust deposition treatments were positively related to aeolian process-induced changes in vegetation cover and species richness, highlighting the important roles of plant community shifts in regulating ecosystem carbon cycling. Our findings suggest that plant traits (for example, canopy height) and soil nutrients may be the key for understanding plant community responses to grassland management and natural hazards.

Asymmetrically seasonal warming has been widely observed on the Earth, but great uncertainties remain for its effects on terrestrial carbon (C) cycling. As a part of a 7-year seasonal warming experiment in an old-field grassland in Central China, this study demonstrated that spring and autumn warming reduced soil respiration by 8.3% and 9.8%, respectively. In addition, spring warming decreased soil respiration by 1.0% and 15.9% without and with autumn warming, respectively. Autumn warming suppressed soil respiration by 2.5% and 17.2% without and with spring warming, respectively. Decreased soil respiration in summer under both spring and autumn warming dominated the treatment-induced suppressions in annual mean soil respiration, which could be primarily attributable to the reductions in plant photosynthesis and growth (aboveground net primary productivity). These observations suggest that the asymmetrically seasonal warming may diminish soil C loss and its feedback to climate warming. Our findings highlight the urgent need of incorporating the interactive and legacy effects of seasonal warming into models used in the IPCC reports for the robust projections of future climate change.

Changing precipitation regimes can profoundly affect plant growth in terrestrial ecosystems, especially in arid and semi-arid regions. However, how changing precipitation, especially extreme precipitation events, alters plant diversity and community composition is still poorly understood. A 3-year field manipulative experiment with seven precipitation treatments, including - 60%, - 40%, - 20%, 0% (as a control), + 20%, + 40%, and + 60% of ambient growing-season precipitation, was conducted in a semi-arid steppe in the Mongolian Plateau. Results showed total plant community cover and forb cover were enhanced with increased precipitation and reduced under decreased precipitation, whereas grass cover was suppressed under the - 60% treatment only. Plant community and grass species richness were reduced by the - 60% treatment only. Moreover, our results demonstrated that total plant community cover was more sensitive to decreased than increased precipitation under normal and extreme precipitation change, and species richness was more sensitive to decreased than increased precipitation under extreme precipitation change. The community composition and low field water holding capacity may drive this asymmetric response. Accumulated changes in community cover may eventually lead to changes in species richness. However, compared to control, Shannon-Weiner index (H) did not respond to any precipitation treatment, and Pielou's evenness index (E) was reduced under the + 60% treatment across the 3 year, but not in each year. Thus, the findings suggest that plant biodiversity in the semi-arid steppe may have a strong resistance to precipitation pattern changes through adjusting its composition in a short term.

Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO2 and nitrogen across major terrestrial vegetation types of the world. Most experiments manipulated single rather than multiple global change drivers in temperate ecosystems of the USA, Europe and China. The magnitudes of warming and elevated CO2 treatments were consistent with the ranges of future projections, whereas those of precipitation changes and nitrogen inputs often exceeded the projected ranges. Increases in global change drivers consistently accelerated, but decreased precipitation slowed down carbon-cycle processes. Nonlinear (including synergistic and antagonistic) effects among global change drivers were rare. Belowground carbon allocation responded negatively to increased precipitation and nitrogen addition and positively to decreased precipitation and elevated CO2. The sensitivities of carbon variables to multiple global change drivers depended on the background climate and ecosystem condition, suggesting that Earth system models should be evaluated using site-specific conditions for best uses of this large dataset. Together, this synthesis underscores an urgent need to explore the interactions among multiple global change drivers in under-represented regions such as semi-arid ecosystems, forests in the tropics and subtropics, and Arctic tundra when forecasting future terrestrial carbon-climate feedback. National Natural Science Foundation of ChinaNational Natural Science Foundation of China [31430015, 31830012]; US NSFNational Science Foundation (NSF) [DEB-0955771]; ClimMani COST actionEuropean Cooperation in Science and Technology (COST) [ES1308] We thank J. Wang (Hebei University), S. Yang (Institute of Botany, Chinese Academy of Sciences), L. Zhou (East China Normal University), C. Qiao (Xinyang Normal University) and H. Li (Henan University) for their help in meta-analyses and interaction analyses, and H. Li, Y. Liu (Institute of Tibetan Plateau Research, Chinese Academy of Sciences) and Y. He (Peking University) for their help in plotting figures. This work was financially supported by the National Natural Science Foundation of China (grant nos. 31430015 and 31830012). This study emerged from the INTERFACE Workshop in Beijing, China (https://www.bio.purdue.edu/INTERFACE/) supported by the US NSF DEB-0955771. We also acknowledge support from the ClimMani COST action (ES1308). Public domain – authored by a U.S. government employee

Anthropogenic environmental changes are known to affect the Earth's ecosystems. However, how these changes influence assembly trajectories of the impacted communities remains a largely open question. In this study, we investigated the effect of elevated nitrogen (N) deposition and increased precipitation on plant taxonomic and phylogenetic β‐diversity in a 9‐year field experiment in the temperate semi‐arid steppe of Inner Mongolia, China. We found that both N and water addition significantly increased taxonomic β‐diversity, whereas N, not water, addition significantly increased phylogenetic β‐diversity. After the differences in local species diversity were controlled using null models, the standard effect size of taxonomic β‐diversity still increased with both N and water addition, whereas water, not N, addition, significantly reduced the standard effect size of phylogenetic β‐diversity. The increased phylogenetic convergence observed in the water addition treatment was associated with colonizing species in each water addition plot being more closely related to species in other replicate plots of the same treatment. Species colonization in this treatment was found to be trait‐based, with leaf nitrogen concentration being the key functional trait. Synthesis. Our analyses demonstrate that anthropogenic environmental changes may affect the assembly trajectories of plant communities at both taxonomic and phylogenetic scales. Our results also suggest that while stochastic processes may cause communities to diverge in species composition, deterministic process could still drive communities to converge in phylogenetic community structure.

Our understanding of how simultaneous climate warming and changing precipitation influence plant phenology in grasslands is still limited. As part of a field transplant experiment, this study was conducted to explore the flowering phenology of the dominant species in three temperate steppes (i.e. a desert, typical, and meadow steppe) along a precipitation gradient in response to simulated night warming and precipitation manipulation (i.e. decreased, ambient, and increased precipitation). Of all monitored species and across three growing seasons (2015–2017), night warming advanced flowering date in the desert and typical steppes, but delayed it in the meadow steppe. Decreased precipitation postponed flowering date but increased precipitation advanced it in all the three steppes. Plant growth largely determined the changes in flowering date under night warming and changing precipitation across and in each of the three steppes. The dominant role of plant growth in modulating reproductive phenology provides mechanistic understanding in interpreting phenological response and facilitate the projections of response of temperate grasslands under future climate change scenarios.

Numerous ecosystem manipulative experiments have been conducted since 1970/80 s to elucidate responses of terrestrial carbon cycling to the changing atmospheric composition (CO2 enrichment and nitrogen deposition) and climate (warming and changing precipitation regimes), which is crucial for model projection and mitigation of future global change effects. Here, we extract data from 2,242 publications that report global change manipulative experiments and build a comprehensive global database with 5,213 pairs of samples for plant production (productivity, biomass, and litter mass) and ecosystem carbon exchange (gross and net ecosystem productivity as well as ecosystem and soil respiration). Information on climate characteristics and vegetation types of experimental sites as well as experimental facilities and manipulation magnitudes subjected to manipulative experiments are also included in this database. This global database can facilitate the estimation of response and sensitivity of key terrestrial carbon-cycling variables under future global change scenarios, and improve the robust projection of global change‒terrestrial carbon feedbacks imposed by Earth System Models., Measurement(s) organic material • plant production • carbon exchange Technology Type(s) digital curation Factor Type(s) climate characteristics • vegetation traits Sample Characteristic - Environment climate system Sample Characteristic - Location global Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12932843

Litter and understory play important roles in maintaining structure and functions of belowground ecosystems in forests. However, how litter and understory affect soil microbial community is unclear. As part of a three-year (2016–2018) manipulative experiment, this study was designed to evaluate the effects of litter and/or understory removal on soil microbial community in a coniferous-broadleaved mixed forest of the subtropical-warm temperate transition zone in Central China. The results showed that soil moisture, NO3−-N, NH4+-N, and dissolved organic carbon were decreased under litter removal, but remained unchanged under understory removal. Total, bacteria, and actinomycetes PLFAs were significantly reduced by 11.2%, 16.3%, and 11.0% under litter removal, and by 10.1%, 13.3%, and 12.5% under understory removal, respectively. Both litter and understory removal suppressed network complexity of soil microbial community, but litter removal showed much stronger impacts on the biomass (−14.9 mg kg−1 vs. −10.9 mg kg−1) and composition (−7.77% vs. −2.89%) of bacteria (including gram-positive and gram-negative bacteria) as well as fungi to bacteria ratio than understory removal. Changes of soil NH4+-N and moisture might be primarily responsible for the inhibitory effects of litter removal on soil gram-positive and gram-negative bacterial biomass, respectively. Our findings highlight the contrasting responses of soil microbial community to litter and understory removal and would facilitate the mechanistic understanding of these two management practices on belowground ecology in climate transitional forests.

Elevated CO2 is widely accepted to enhance terrestrial carbon sink, especially in arid and semi-arid regions. However, great uncertainties exist for the CO2 fertilisation effects, particularly when its interactions with other global change factors are considered. A four-factor (CO2 , temperature, precipitation and nitrogen) experiment revealed that elevated CO2 did not affect either gross ecosystem productivity or ecosystem respiration, and consequently resulted in no changes of net ecosystem productivity in a semi-arid grassland despite whether temperature, precipitation and nitrogen were elevated or not. The observations could be primarily attributable to the offset of ecosystem carbon uptake by enhanced soil carbon release under CO2 enrichment. Our findings indicate that arid and semi-arid ecosystems may not be sensitive to CO2 enrichment as previously expected and highlight the urgent need to incorporate this mechanism into most IPCC carbon-cycle models for convincing projection of terrestrial carbon sink and its feedback to climate change.

Responses and feedbacks of ecosystem carbon (C) cycling in the terrestrial biosphere to climate change pose the major challenge for Earth System Model projections. However, whether ecosystem C cycling among diverse vegetation types shows different sensitivities and the associated underlying mechanisms remain elusive. As part of a 5-year (2014–2018) soil monolith transplant experiment, this study was designed to examine the influences of night warming, decreased precipitation, and increased precipitation on soil respiration in the three temperate steppes (i.e. desert, typical, and meadow steppes) along a precipitation gradient on the Mongolian Plateau. Over the 5 years, night warming had no effect on soil respiration in any of the three steppes. Decreased precipitation reduced soil respiration, whereas increased precipitation stimulated it in each steppe. In addition, the sensitivity of soil respiration to increased precipitation was larger than that to decreased precipitation, suggesting a positive asymmetry of soil respiration in response to changing precipitation. The soil respiration responses were predominately determined by both soil water availability and belowground net primary productivity in the desert and typical steppes, but by soil total C alone in the meadow steppe. These findings not only improve mechanistic understanding on the responses of soil respiration in various grassland ecosystems, but also facilitate the extrapolation from local to regional scale for the robust projections of terrestrial C-climate change feedbacks.

Elevated CO

Changing precipitation regimes could have profound influences on carbon (C) cycle in the biosphere. However, how soil C release from terrestrial ecosystems responds to changing seasonal distribution of precipitation remains unclear. A field experiment was conducted for 4 years (2013-2016) to examine effects of altered precipitation distributions in the growing season on soil respiration in a temperate steppe in the Mongolian Plateau. Over the 4 years, both advanced and delayed precipitation peaks suppressed soil respiration, and the reductions mainly occurred in August. The decreased soil respiration could be primarily attributable to water stress and subsequently limited plant growth (community cover and belowground net primary productivity) and soil microbial activities in the middle growing season, suggesting that precipitation amount in the middle growing season is more important than that in the early, late or whole growing seasons in regulating soil C release in grasslands. The observations of the additive effects of advanced and delayed precipitation peaks indicate semiarid grasslands will release less C through soil respiratory processes under the projected seasonal redistribution of precipitation in the future. Our findings highlight the potential role of intra-annual redistribution of precipitation in regulating ecosystem C cycling in arid and semiarid regions. This article is protected by copyright. All rights reserved.