Community Temporal Stability Research Articles

Grazing and selenium influence community stability by increasing asynchrony and sedge, forbs stability in alpine meadow of Qinghai-Tibet Plateau

Grazing is a major driving force of biodiversity, functions and stability of alpine meadows. In selenium-deficient alpine meadows, moderate selenium supplementation can promote plant growth and increase selenium content within the food web. However, the combined effect of grazing and selenium (Se) addition on the stability of alpine meadow communities within selenium-deficient soil is still unclear. Therefore, we conducted a three-year experiment in an alpine meadow of Qinghai-Tibetan Plateau (QTP), with two stocking rates (0 and 6 sheep months ha−1) and six levels of Se addition (0, 5, 10, 20, 40 and 80 g ha−1) to explore how grazing and Se addition affect community stability and its relationship with species richness, species asynchrony and functional group stability. Results showed that the community stability, species richness and biomass response ratio of the community increased gradually with the increase in the selenium application under grazing and enclosure treatments, reaching the maximum values at 20 g ha−1. However, when the selenium addition exceeded 20 g ha−1, the above mentioned indexes were decreased gradually, especially under grazing. Structural equation model showed that grazing and selenium addition indirectly affected the temporal stability of sedges and forbs, thus influencing the temporal stability of the community. Results of this study indicated that the alpine meadow can maintain high species diversity and community temporal stability under moderate grazing combined with selenium addition, providing a scientific basis for selenium-enriched grazing management in alpine meadows.

Temporal stability responses to nitrogen addition in Xizang alpine grasslands: A community composition perspective

Plant community composition typically undergoes progressive changes along environmental gradients. However, most experimental studies have focused on individual communities, so it remains unclear how exogenous nutrient inputs affect the stability of plant communities along environmental gradients. Along a rainfall gradient on the northern Xizang Plateau, we conducted an 8-year nitrogen (N) addition experiment in four alpine grasslands (alpine desert steppe, ADS; alpine steppe, AS; alpine meadow steppe, AMS; and alpine meadow, AM) and used two-way ANOVA to examine the effects of N addition on the temporal stability of these different alpine grasslands. We found that community aboveground biomass showed saturation trends in AM and AMS with increasing N gradients, while there was no change in AS and a gradual increase in ADS. The temporal stability showed different patterns of gradual decreases in ADS and AM, and a unimodal trend in AMS with increasing N gradients. However, N addition had no effect on the temporal stability of AS. Dominant species stability was the controlling factor for alpine grasslands along the transect, while the effect of asynchrony gradually increased with decreasing precipitation. These findings highlight that community composition, especially the dominant species, along the environmental gradient can mediate the effects of N inputs on community temporal stability. Thus, the conservation and restoration of the dominant species are particularly important under future scenarios of increased atmospheric N deposition.

Increase in precipitation will facilitate the ecological stability of desert steppe in the future

Community stability plays a vital role in ensuring the consistent provision of ecosystem services despite climatic changes. It is presumed that future changes to annual precipitation will impact the ecological stability of many systems, particularly the ‘fragile’ desert steppe. However, most studies of ecological stability are inferred from short-term field precipitation manipulation experiments. There is still extensively to learn regarding how the desert steppe reacts to long-term changes in precipitation. We conducted a 7-year experimental study monitoring the aboveground biomass of major plant functional groups (perennial grasses, perennial forbs, annual herbs, and semi-shrubs) under four experimentally manipulated precipitation gradients [reducing natural precipitation by 50% (-50%), natural precipitation (CK), increasing natural precipitation by 50% (+50%), and increasing natural precipitation by 100% (+100%)] to evaluate how changes in precipitation affect the biomass stability of plant communities. We did observe higher levels of species asynchrony, resistance, resilience, and temporal stability of community and functional groups in experimental plots receiving more precipitation. Interestingly, the contribution of species richness to community stability was not observed in our experiment. The increase in soil water content in the 20–30 cm soil layer caused by increased precipitation promoted the resilience of perennial grasses but inhibited the resistance of perennial forbs. At the same time, the decrease in soil inorganic nitrogen caused by increased rainfall inhibited the resilience of perennial grasses. Notably, community resilience predominantly hinged on the resilience of perennial grasses, while community resistance was primarily dictated by the resistance of perennial forbs. Moreover, species asynchrony emerged as the primary regulator of community temporal stability. Our long-term experimental evidence underscores the transformative potential of precipitation in reshaping grassland stability across both functional and structural dimensions. Importantly, sustaining the high stability of perennial herbs emerges as a strategic avenue for enhancing the ecological stability of the desert steppe in the face of evolving precipitation patterns.

Divergent driving mechanisms of community temporal stability in China's drylands

Climate change and anthropogenic activities are reshaping dryland ecosystems globally at an unprecedented pace, jeopardizing their stability. The stability of these ecosystems is crucial for maintaining ecological balance and supporting local communities. Yet, the mechanisms governing their stability are poorly understood, largely due to the scarcity of comprehensive field data. Here we show the patterns of community temporal stability and its determinants across an aridity spectrum by integrating a transect survey across China's drylands with remote sensing. Our results revealed a U-shaped relationship between community temporal stability and aridity, with a pivotal shift occurring around an aridity level of 0.88. In less arid areas (aridity level below 0.88), enhanced precipitation and biodiversity were associated with increased community productivity and stability. Conversely, in more arid zones (aridity level above 0.88), elevated soil organic carbon and biodiversity were linked to greater fluctuations in community productivity and reduced stability. Our study identifies a critical aridity threshold that precipitates significant changes in community stability in China's drylands, underscoring the importance of distinct mechanisms driving ecosystem stability in varying aridity contexts. These insights are pivotal for developing informed ecosystem management and policy strategies tailored to the unique challenges of dryland conservation.

Long‐term stability of sapling dynamics is regulated by soil phosphorus availability in subtropical forest

Abstract The abiotic and biotic factors that regulate stability in species‐rich forests are poorly resolved, and this limits the ability to predict how climate change and other perturbations impact forest dynamics. Phosphorus limitation and nitrogen deposition are important factors affecting the dynamics and functioning of tropical and subtropical forests, but how long‐term temporal stability of tree communities is affected by availability and heterogeneity of soil phosphorus and nitrogen remains unclear. We collected annual dynamic data of 20,768 regenerating saplings, which were censused from 2008 to 2019 in a subtropical forest, to investigate how soil nutrients affect the temporal stability of productivity at both population and community levels. We found that concentrations of soil inorganic phosphorus were significantly and positively correlated with sapling richness and phylogenetic diversity, leading to significantly higher species asynchrony and community temporal stability. By contrast, higher concentrations of organic phosphorus weakened community stability via a negative effect on species richness. Structural equation models provide further strong evidence that increasing concentrations of soil inorganic phosphorus strongly promoted community temporal stability via increased species diversity, species asynchrony and population stability, while organic phosphorus displayed opposite effects. Meanwhile, soil concentrations of available and unavailable forms of nitrogen showed much weaker and negative associations with community stability. Synthesis. Using a 12‐year data set of sapling demography from a subtropical forest of south China, our study demonstrates that soil phosphorus is an important determinant of the long‐term stability of sapling dynamics and consequently the whole‐community structure, and the composition of soil phosphorus pools predicts the temporal stability and diversity of tree communities in phosphorus‐limited forests.

Fungal pathogens increase community temporal stability through species asynchrony regardless of nutrient fertilization.

Natural enemies and their interaction with host nutrient availability influence plant population dynamics, community structure, and ecosystem functions. However, the nature in which these factors influence patterns of community stability, as well as the direct and indirect processes underlying that stability, remain unclear. Here, we investigated the separate and interactive roles of fungal/oomycete pathogens and nutrient fertilization on the temporal stability of community biomass and the potential mechanisms using a factorial experiment in an alpine meadow. We found that fungal pathogen exclusion reduced community temporal stability mainly through decreasing species asynchrony, while fertilization tended to reduce community temporal stability through decreasing species stability. However, there was no interaction between pathogen exclusion and nutrient fertilization. These effects were largely due to the direct effects of the treatments on plant biomass, and not due to indirect effects mediated through plant diversity. Our findings highlight the need for a multi-trophic perspective in field studies examining ecosystem stability.

Grazing and precipitation addition reduces the temporal stability of aboveground biomass in a typical steppe of Chinese Loess Plateau

Few studies on the effects of human activities and global climate change on temporal stability have considered either grazing or precipitation addition (PA). How community stability responds to the interaction between PA and grazing in a single experiment remains unknown. We studied the impact of grazing and PA on the temporal stability of communities in four years field experiment conducted in a typical steppe, adopting a randomized complete block design with grazing was the main block factor and PA was the split block factor. Grazing and PA had negative impacts on the temporal stability of communities. PA reduced the community stability through decreasing the stability of subordinate and community species richness (SR), whereas grazing reduced the community stability through decreasing the stability of the SR and dominant species. In contrast, grazing and PA maintained community stability through increasing species asynchronism and promoting the decoupling of asynchronism and stability. Our results revealed the different mechanisms of grazing and PA on community stability. Exploring the response characteristics of population dynamics to global climate change and pasture management is key to understanding future climate scenarios and changes in community stability under grazing.

Shifts in dominant species modulate nitrogen effects on community temporal stability along a degradation gradient in Tibetan alpine grasslands

Grassland degradation is a widespread concern globally. Nutrient addition is widely recognized as an important management measure for degraded grassland restoration, but nutrient inputs may have important effects on temporal stability of communities. However, it is unclear how the degradation degrees regulate the impacts of adding nitrogen (N) on temporal stability of communities due to large variations in community composition and soil nutrient content. Herein, long-term experimental study was used to identify the N influences on temporal stability of community and driving factors of alpine grasslands at three degradational stages (none (ND), moderate (MD), and heavily degraded grassland (HD)). Elevated N could significantly enhance the aboveground biomass of ND, while there was no notable effect on MD and HD. However, N addition significantly lowered the temporal stability of all these three grasslands, although species richness was only pronouncedly reduced in MD. Our most conspicuous outcome is the major mechanism of temporal stability of community varied with degradation stages. N addition decreased temporal stability of the community predominantly by decrease in the richness of species and the stability of dominant species in ND and MD while decrease in dominant species stability, asynchrony, and richness of species in HD. This study highlights that impacts of N enrichment on temporal stability of community are potentially intermediated via community composition of alpine grasslands, which can offer guidance for scientific management and rehabilitation of degraded alpine grasslands.

Biodiversity stabilizes plant communities through statistical-averaging effects rather than compensatory dynamics

Understanding the relationship between biodiversity and ecosystem stability is a central goal of ecologists. Recent studies have concluded that biodiversity increases community temporal stability by increasing the asynchrony between the dynamics of different species. Theoretically, this enhancement can occur through either increased between-species compensatory dynamics, a fundamentally biological mechanism; or through an averaging effect, primarily a statistical mechanism. Yet it remains unclear which mechanism is dominant in explaining the diversity-stability relationship. We address this issue by mathematically decomposing asynchrony into components separately quantifying the compensatory and statistical-averaging effects. We applied the new decomposition approach to plant survey and experimental data from North American grasslands. We show that statistical averaging, rather than compensatory dynamics, was the principal mediator of biodiversity effects on community stability. Our simple decomposition approach helps integrate concepts of stability, asynchrony, statistical averaging, and compensatory dynamics, and suggests that statistical averaging, rather than compensatory dynamics, is the primary means by which biodiversity confers ecological stability.

Temporal change in community temporal stability in response to mowing and nutrient enrichment: evidence from a 15-year grassland experiment

Abstract 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.

Species richness and asynchrony maintain the stability of primary productivity against seasonal climatic variability.

The stability of grassland communities informs us about the ability of grasslands to provide reliable services despite environmental fluctuations. There is large evidence that higher plant diversity and asynchrony among species stabilizes grassland primary productivity against interannual climate variability. Whether biodiversity and asynchrony among species and functional groups stabilize grassland productivity against seasonal climate variability remains unknown. Here, using 29-year monitoring of a temperate grassland, we found lower community temporal stability with higher seasonal climate variability (temperature and precipitation). This was due to a combination of processes including related species richness, species asynchrony, functional group asynchrony and dominant species stability. Among those processes, functional group asynchrony had the strongest contribution to community compensatory dynamics and community stability. Based on a long-term study spanning 29 years, our results indicate that biodiversity and compensatory dynamics a key for the stable provision of grassland function against increasing seasonal climate variability.

Different responses of community temporal stability to nitrogen and phosphorus addition in a non-degraded alpine grassland

Fertilization has been widely used in grassland management, but different types of fertilizers may have inconsistent impacts on grassland productivity and stability. However, less is known about the responses of plant community stability and the shifts of driving mechanisms under different fertilizers. We conducted a long-term nitrogen (N) and/or phosphorus (P) addition experiment in an alpine steppe meadow, using two N levels (5 (N5), 10 (N10) g N/m−2(−|-) year−1), one P level (5 g N m−2 year−1, P5) and the combined treatments (N5P5 and N10P5), to examine their effects on community temporal stability and the underlying mechanisms. Both N addition alone and the combined addition significantly increased community aboveground biomass, while P5 did not affect community aboveground biomass. However, only N10, N5P5, and N10P5 decreased annual average species richness, while other treatments showed no pronounced effect. Except for N5, community stability decreased under both N and P additions. The most remarkable finding is that the driving mechanisms underlying community stability shifted with nutrient types. The decrease in species richness induced by N addition decreased community stability. However, the decrease in dominant species asynchrony induced by P addition affected community asynchrony, which contributed to the decrease in community stability. N and P combined addition could additively affect community stability both by species richness and dominant species asynchrony and further community asynchrony. Our results indicate that fertilizer types can alter the regulatory effect of plant diversity on community stability. This study reveals that attention should be paid to the different mechanisms driving community stability under different nutrient types, which provides a scientific basis for alpine grassland management.

Winter warming alleviates the severely negative effects of nitrogen addition on ecosystem stability in a Tibetan alpine grassland

Many recent studies have explored how global warming and increased nitrogen (N) deposition affect the structure and function of natural ecosystems. However, how ecosystems respond to the combination of warming and N enrichment remains unexplored, especially under asymmetric seasonal warming scenarios. We conducted a decade-long field experiment in an alpine grassland to investigate the effects of warming (ambient condition (NW), winter-only (WW), and year-round (YW) warming) and N addition on the temporal stability of communities. Although N addition significantly reduced community temporal stability in NW, WW, and YW, WW relieved the severely negative effects of N addition compared to NW and YW (from 47.7 % in NW and 76.1 % in YW to 18.6 % in WW under 80 kg N hm−2 year−1). The most remarkable finding is that the main factors driving community stability shifted with warming patterns. The increase in community dominance under NW was a significant driver of the decreased temporal stability in the community. However, the decrease in community stability caused by N addition was ascribed to the decreased stability of both dominant and common species under WW. In contrast, N addition decreased community temporal stability mainly via a decrease in species asynchrony under YW. Our results suggested that warming patterns can modulate the effects of N enhancement on community stability. To predict the effects of climate change on alpine grasslands accurately, the idiosyncratic effects of asymmetric seasonal warming under future climate change scenarios should be considered.

Multiple global changes drive grassland productivity and stability: A meta‐analysis

Abstract Temporal stability of primary productivity is the key to stable provisioning of ecosystem services to human beings. Yet, the effects of various global changes on grassland stability remain ambiguous. Here, we conducted a comprehensive meta‐analysis based on 1070 multi‐year paired observations from 173 studies, to examine the impacts of various global changes on productivity, community stability and plant diversity of grasslands on a global scale. The global change drivers include nitrogen (N) addition, phosphorus (P) addition, N and P addition, precipitation increase, precipitation decrease, elevated CO2 and warming. Global change drivers generally had stronger impacts on grassland productivity than on temporal stability, except for precipitation changes. Community temporal stability was reduced by N addition, N and P addition and precipitation decrease, but was increased by precipitation increase and remained unchanged under P addition, elevated CO2 and warming. In addition, species richness decreased under N addition, N and P addition and precipitation decrease. At the plant functional group level, N and P addition reduced grasses' stability and precipitation increase enhanced forbs' stability. Nutrient additions decreased community stability via increasing the inter‐annual variation more than the mean of primary productivity, while precipitation changes mainly affected community temporal stability via changing mean productivity. The negative impacts of global change drivers (i.e. N and P addition, warming) on community temporal stability increased with the degree of species loss but decreased with increasing stability of grasses. Moreover, the negative impacts of nutrient addition and precipitation decrease on community stability was lessened while the positive effect of precipitation increase on community stability was enhanced in grasslands with higher historical precipitation variability, greater soil fertility and longer experimental duration. Synthesis. Our findings demonstrate that N‐based nutrient additions and drought destabilise grassland productivity, while precipitation increase enhances community stability. Impacts of global changes on community productivity and stability are mediated by species richness, plant functional group, site‐specific environmental conditions (i.e. climate, soil) and experimental duration, which deserve more attention in grassland management practices under future global change scenarios.

Temporal stability and maintenance mechanisms of alpine meadow communities under clipping and fertilization.

Negative effects of long‐term overgrazing have been seriously, grasslands temporal stability is an important ecological concern we need to research. Here, we performed a 12‐year‐long (2007–2018) two‐factor controlled experiment on Kobresia humilis meadow on the Tibetan Plateau. The manipulations included three clipping levels (no clipping, NC; moderate clipping, MC; heavy clipping, HC) and two fertilization levels (no fertilization, NF; fertilization, F). Our results revealed that the two clipping manipulations significantly increased the temporal stability of alpine meadow communities, whose significant increase was more pronounced under the MC than HC treatment. Species asynchrony had a significant positive correlation with species abundance along with compound community gradient. Moreover, asynchrony effects, portfolio effects, and facilitation interactions were all present in the communities under the six types of experimental treatment combinations. Additionally, a selection effect was detected in the compound communities, demonstrating characteristics that are common to different mechanisms. There were no significant differences in the effects of these mechanisms on community temporal stability between the NC–NF and MC–NF interactive communities. The portfolio effects predominated when clipping intensity was moderate under both fertilization and nonfertilization conditions. By contrast, in the compound communities, the selection effect predominated. In summary, we conclude that in meadow communities that undergo clipping and fertilization disturbances, facilitation interactions and weak interactions make a greater contribution toward maintaining their temporal stability.

Heavy grazing disrupts positive effects of arbuscular mycorrhizae symbiosis on community productivity and stability under low and high phosphorus conditions

We quantified the potential influence of arbuscular mycorrhizal fungi (AMF) on primary productivity and community stability and tested whether the effects of AMF depend on soil phosphorus (P) availability and grazing intensity in a semiarid grassland. We manipulated the abundance of AMF and soil P availability (P addition and no P addition) under four levels of grazing intensity. The aboveground biomass of plant species, functional groups and community, as well as community temporal stability were examined under these conditions. Under no to moderate grazing, benomyl decreased the aboveground biomass in C4 grasses and forbs, but increased the aboveground biomass in C3 grasses under low P conditions; thus no obvious changes in community primary productivity were observed. These results indicated that the mycorrhizal dependency of C4 grasses and forbs is higher than that of C3 grasses under low P conditions. However, community primary productivity was greatly enhanced by benomyl due to the increased biomasses of C3 grasses and forbs under high P conditions. Under heavy grazing conditions, benomyl increased community primary productivity under both low and high P conditions. AMF presence increased the community temporal stability by promoting the compensatory effects between plant species under no to moderate grazing conditions; whereas AMF decreased the community stability by forming a parasitic symbiosis with their plant hosts under heavy grazing conditions. Our findings demonstrate that the effects of benomyl application to suppress AMF on primary productivity and community stability are strongly mediated by soil P availability and grazing intensity, which improves our understanding for the roles of AMF-plant symbiosis on ecosystem functioning in grazed systems.

Suppression of arbuscular mycorrhizal fungi decreases the temporal stability of community productivity under elevated temperature and nitrogen addition in a temperate meadow

Global change alters how terrestrial ecosystems function and makes them less stable over time. Global change can also suppress the development and effectiveness of arbuscular mycorrhizal fungi (AMF). This is concerning, as AMF have been shown to alleviate the negative influence of global changes on plant growth and maintain species coexistence. However, how AMF and global change interact and influence community temporal stability remains poorly understood. Here, we conducted a 4-year field experiment and used structural equation modeling (SEM) to explore the influence of elevated temperature, nitrogen (N) addition and AMF suppression on community temporal stability (quantified as the ratio of the mean community productivity to its standard deviation) in a temperate meadow in northern China. We found that elevated temperature and AMF suppression independently decreased the community temporal stability but that N addition had no impact. Community temporal stability was mainly driven by elevated temperature, N addition and AMF suppression that modulated the dominant species stability; to a lesser extent by the elevated temperature and AMF suppression that modulated AMF richness associated with community asynchrony; and finally by the N addition and AMF suppression that modulated mycorrhizal colonization. In addition, although N addition, AMF suppression and elevated temperature plus AMF suppression reduced plant species richness, there was no evidence that changes in community temporal stability were linked to changes in plant richness. SEM further showed that elevated temperature, N addition and AMF suppression regulated community temporal stability by influencing both the temporal mean and variation in community productivity. Our results suggest that global environmental changes may have appreciable consequences for the stability of temperate meadows while also highlighting the role of belowground AMF status in the responses of plant community temporal stability to global change.

Mycorrhizal fungi maintain plant community stability by mitigating the negative effects of nitrogen deposition on subordinate species in Central Asia

AbstractQuestionsPlant community stability is threatened by increasing numbers of simultaneously changing factors such as increased precipitation and nitrogen (N) deposition. Despite the pivotal roles of arbuscular mycorrhizal fungi (AMF) for plant community dynamics, only few studies have paid attention to their roles in maintaining plant community stability under global change. We therefore assessed the interactive effects of a realistic N deposition and AMF on plant community temporal stability under future increased precipitation scenarios.LocationGurbantunggut desert, China.MethodsWe conducted a four‐year field experiment simulating a realistic N deposition and with/without AMF treatments in one typical ephemeral plant community, dynamically monitoring the changes in plant community biomass and composition.ResultsWe found that suppression of AMF significantly reduced Shannon–Wiener diversity and evenness while the realistic N deposition only marginally reduced the Shannon–Wiener diversity. Suppression of AMF and increased N deposition highly increased the species turnover. Particularly, the stability of subordinate plant species significantly correlated to the community‐level stability. AMF were able to buffer the negative effects of increased N deposition on plant community diversity, to maintain community‐level stability.ConclusionsOur study supports the subordinate insurance hypothesis, highlighting the considerable roles of subordinate plant species in maintaining community stability. Furthermore, our results indicate the joint roles of AMF and N deposition in regulating plant community stability, and point to the importance of taking AMF and the realistic N deposition into account for understanding the responses of community stability to multiple global change scenarios.

Plant community temporal stability in response to nitrogen addition among different degraded grasslands

Atmospheric nitrogen (N) deposition is generally believed to decrease plant community temporal stability. However, it remains unclear whether the responses of community temporal stability to N deposition vary with disturbance regimes, such as among different grasslands with degrees of degradation. We established a 4-year field experiment with six N addition levels on four grassland sites in northern China with varying degradation statuses (non-degraded, moderately, severely and extremely degraded grasslands). We examined the response of community temporal stability (quantified as the ratio of the mean of community biomass to its standard deviation) to N addition and important regulating factors. Asynchrony was calculated as the difference between one and synchrony (quantified as the ratio of the variance of community biomass to the square of the sum of the standard deviation of species biomass). The most interesting result we found was that community temporal stability of the moderately and severely degraded grasslands was relatively higher among the four grasslands without N addition. This was attributed to shifts in dominant species composition rather than species diversity. Community temporal stability of nearly all sites were not significantly affected by N addition except the moderately degraded grassland. Community temporal stability of the moderately degraded grassland responded to N addition non-linearly, being promoted by low N addition levels (10 and 20 g N m−2 yr−1) and decreased by high N addition levels (30–50 g N m−2 yr−1). Furthermore, community temporal stability of the non-degraded and moderately degraded grasslands was mainly driven by species asynchrony. Whereas, in the severely and extremely degraded grasslands, community temporal stability was mainly regulated by species richness and dominant species stability, respectively. These findings highlight the importance of grassland degradation in the response of community temporal stability to N deposition and provide scientific support for the management and restoration of degraded grasslands.

Temporal stability of aboveground biomass is governed by species asynchrony in temperate forests.

Understanding the effects of plant species diversity and trait composition on aboveground biomass is a central focus of ecology and has important implications for biodiversity conservation. However, the simultaneous direct and indirect effects of soil nutrients, species asynchrony, functional trait diversity, and trait composition for explaining the community temporal stability of aboveground biomass remain underrepresented in natural forests. Here, we hypothesized that species asynchrony relative to soil nutrients, functional trait diversity, and trait composition plays a central role in stabilizing the community temporal stability of natural forests. We tested this hypothesis using a structural equation model based on 10-year continuous monitoring data (i.e., three-time repeated forest inventories) in both second-growth and old-growth temperate forests in northeast China. Our results showed that the community temporal stability of aboveground biomass was driven by a strong direct positive effect of species asynchrony in both second-growth and old-growth temperate forests, whereas functional trait diversity and composition (i.e. community-weighted mean of leaf nitrogen content) were of additional importance in an old-growth forest only. Functional trait diversity decreased community-weighted mean of leaf nitrogen content in an old-growth forest, whereas this relationship was non-significant in a second-growth forest. Soil nutrients had non-significant effects on the community temporal stability of both second-growth and old-growth forests. Species asynchrony was the direct determinant of the community temporal stability of aboveground biomass in temperate forests. The direct effect of species asynchrony increased with forest succession, implying that temporal niche differentiation and facilitation increase over time. This study suggests that managing forests with mixtures of both early and late successional species or shade intolerant and tolerant species, not only species diversity, is important for maintaining forest stability in a changing environment. We argue that the species asynchrony effect is crucial to understand the underlying ecological mechanisms for a diversity-biomass relationship in natural forests.