Aims The spatial distributions and associations of tree species offer valuable insights into interspecies relationships and their interplay with the surrounding environment. These insights are critical for understanding community assembly and species coexistence.

Methods To investigate the spatial distribution patterns of the tree species in the mid-mountain moist evergreen broadleaf forest in the south of Gaoligong Mountains, the spatial distributions and interspecies associations of ten dominant species were analyzed by using the point pattern analyses for all woody plants with diameter at breast height ≥ 1 cm in a 4 hm² plot.

Important findings Our results showed: (1) All ten dominant species and the overall tree population exhibited a J-shaped diameter class distribution, indicating growing populations with successful recruitment. (2) Under the complete spatial randomness with univariate pairwise correlation functions, the small-scale patterns of species distribution were aggregated. This aggregation weakened with increasing scale, resulting in random and uniform distribution at larger scales. After accounting for environmental heterogeneity, the range of aggregation was reduced, while the range of random and uniform distribution expanded. (3) Bivariate pairwise correlation function tests under complete spatial randomness null model demonstrated that interspecies correlations were dominated by significant positive associations, while become no significant association under heterogeneous Poisson null model. In conclusion, the distribution patterns and correlations of ten dominant species in Gaoligong Mountains varied with spatial scale, further emphasizing the strong scale-dependency of species distributions. This suggests that forests in Gaoligong Mountains were influenced by several factors, such as dispersal limitation, negative density dependence, and habitat heterogeneity.

Aims Biodiversity is important for maintaining multiple ecosystem functions and enhancing community resilience to disturbance. Selection effect and niche complementarity effect are two widely discussed mechanisms for maintaining ecosystem function, but the understanding of how these two mechanisms maintain forest ecosystem multifunctionality (EMF) under climate change is still limited. It is essential to deepen our understanding of these mechanisms, particularly in assessing whether there are differences in their effectiveness across different climatic zones.

Methods Based on plots distributed in natural forests of middle temperate and cold temperate zones in northeastern China, we used functional trait diversity (FD_{q= 0}), single and multidimensional trait functional dispersion indices (FDis) to represent the niche complementarity effect, and community weighted mean trait values (CWM) to represent the selection effect. We also explored the driving force of EMF to climate change by using multivariate linear models and partial least squares path modeling (PLS-PM; structural equation model).

Important findings (1) In middle temperate forests, two attributes of biodiversity (tree species diversity (SR) and FD_{q= 0}) had significant positive effects on EMF, and FD_{q= 0} had stronger effects than SR. In cold temperate forests, no significant relationship between biodiversity and EMF (BEMF) was found. (2) In middle temperate forest communities, the effects of SR on EMF were mediated by trait differences and community weighted mean maximum tree height (CWM_Hmax) value. Both selection effect and niche complementarity effect simultaneously maintained EMF in middle temperate forests, with selection effect slightly higher than complementarity effect. CWM_Hmax was the main biotic factor influencing cold temperate forest EMF, and selection effect was the main driving force on EMF in these forests. SR and trait differences did not have a significant promoting effect on EMF. (3) Due to the “insurance effect” of biodiversity, middle temperate forests had a stronger resistance to climate change. Climate factors had no significant impact on SR, trait differences, CWM_Hmax and EMF. However, cold temperate forests were sensitive to climate change, and climatic factors were important abiotic factors affecting EMF. Higher annual mean air temperature and precipitation significantly altered community trait composition (e.g., CWM_Hmax), diluting the contribution of species with high competitiveness and fitness traits (e.g., maximum tree height (H_max) trait) to ecosystem functions, and reducing the strength of the selection effect. This study highlights the importance of biodiversity for maintaining forest EMF, and demonstrates that both selection effect and complementarity effect are driving forces for temperate forest EMF in northeastern China.

Plant-soil feedback experiment is an important way for studying plant-soil biota interactions. Plant growth can change soil physical, chemical, and biotic properties in ways that then alter subsequent plant performance, population fluctuation, and community dynamics. This process, referred to as “plant-soil feedback” (PSF), might play a key role in biodiversity maintenance, sustainable agriculture development, and ecological restoration. In this review, we first provide an overview of the concept and research methods of PSF. Second, we review the research progress of the role of PSF in the maintenance of plant species diversity, plant community succession, plant invasions and range shifts, ecological response to climate change, above- and below-ground multitrophic interactions, ecosystem restoration, and crop performance in different cropping systems. We suggest three directions for future PSF studies, including: (1) the transition from single-species to community-level interactions between plants and soil biota; (2) the test of PSF experiments in field conditions; (3) the expansion of theoretical knowledge into ecological practice.

Aims Biodiversity loss threatens ecosystem functions. Investigating the effect of biodiversity on the ecological stoichiometry of plant nutrients, therefore, can help reveal the mechanisms of the effect of biodiversity on ecosystem functions.

Methods Using a tree species diversity experiment in subtropical China, Cunninghamia lanceolatafrom plots with different tree species richness (1, 4, 8, 16, 32) were selected as focal tree species. The effects of neighborhood species richness (NSR), functional trait dissimilarities between neighborhood tree species and the focal tree, neighborhood competition index (NCI) on foliar nitrogen (N), phosphorus (P) content and N:P of C. lanceolata were investigated.

Important findings (1) The results showed that the dissimilarity in specific root length (SRL_diss) between neighborhood trees and focal trees significantly increased the foliar P content of C. lanceolata, while the dissimilarity in root tissue density (RTD_diss) significantly decreased the foliar N content of C. lanceolata. (2) Neighborhood competition significantly decreased the foliar N content and N:P of C. lanceolata. (3) The interaction effects of NCI and SRL_diss, as well as the interaction between NSR and SRL_diss significantly reduced the foliar P content of C. lanceolata. The result indicates that the positive effect of SRL_diss on the foliar P content of C. lanceolata decreased with increasing NSR, and the positive effect of SRL_diss on the foliar P content of C. lanceolata decreased with increasing NCI. (4) The interaction between NSR and phylogenetic dissimilarity (NP_diss) significantly increased foliar N:P of C. lanceolata, demonstrating that the negative effect of NP_diss on the foliar N:P content of C. lanceolata decreased with increasing NSR. Our results indicated that the foliar P content of C. lanceolata was significantly enhanced by mixing with tree species with different trait dissimilarities, while foliar N content of C. lanceolata was decreased by neighborhood competition. Tree species richness can help mitigate the adverse effects of interspecific competition on C. lanceolata through niche complementation when mixing with species that have greater trait dissimilarity.

In forest ecosystems, vascular epiphytes in the forest canopy act as buffers against environmental pressures, create important habitats for other organisms, increase the complexity of forest ecosystems, and enhance species diversity and community stability. Vascular epiphytes can create distinct habitat forms and perform unique ecological functions. Based on their morphological functional characteristics, they can be categorized into two groups: collecting plants and ant-nest plants. The former group includes “trash-basket” and “tank-form” plants, while the latter group includes “ant-garden” and “ant-house” plants. The present paper discusses the positive effect of vascular epiphytes on canopy biodiversity through the creation of habitats. It reveals the existence of these microhabitats can increase the complexity of the canopy community structure and food web, thereby promoting community stability. Additionally, we analyze how herbivorous defense and nutrient acquisition promote the evolution of special structures of vascular epiphytes for creating habitats, and the impact of these structures on the evolution of other canopy organisms. Drawing on the current research hotspots in canopy science, this paper explores the role of habitat-constructing vascular epiphytes in the three prominent areas: biological interactions in forest canopies, community succession, and responses to global change. This paper highlights the role of habitat-constructing vascular epiphytes as “umbrella species” with significant conservation value in the face of global change. We suggested to strengthen the research on the evolutionary history and ecological functions of different types of vascular epiphytes, and to explore the biodiversity conservation strategies for tropical and subtropical forests ecosystems in the context of global change.

Aims The relationship between biodiversity and ecosystem function is one of the hotspots in ecological research. In the past, the research on the relationship between biodiversity and ecosystem function only focused on the experimental or observational investigation of single ecosystem function (SEF), ignoring the most essential value that ecosystem can provide multiple functions and services at the same time. Identifying the relationship between plant functional diversity and ecosystem multifunctionality (EMF) can provide a clear understanding of changes in ecosystem function.

Methods In this study, Bayanbulak alpine meadow was taken as the study area, and five altitude sites were set at an interval of 200 m from 2 194 to 3 062 m above sea level. Soil total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, total phosphorus content, available phosphorus content, total potassium content, available potassium content, soil density, aboveground and underground biomass of plant community were selected to characterize EMF, which were closely related to nutrient cycling, soil organic carbon accumulation and plant growth.

Important findings (1) The species composition of the plant community varied greatly along the altitude gradient, and the species richness at the altitude of 2 600 m was significantly higher than that at the other altitudes. Functional evenness index (FEve), functional richness index (FRic) and functional dispersion index (FDis) all showed a “single peak” trend with the rise of altitude, and the highest values were found at 2 600, 2 800 and 2 800 m, respectively. Rao’ quadratic entropy (Rao’Q) showed a monotonically decreasing trend. (2) FRic and FDis at each altitude were positively correlated with soil EMF, which accounted for 47% and 43% of the variation in EMF, respectively. FEve was significantly correlated with nutrient cycling index and soil organic carbon storage index at the altitude of 2 600 m. Rao’Q at 3 000 m was significantly correlated with soil nutrient cycling index, organic carbon storage and EMF. The relationship between plant functional diversity and EMF along the altitude gradient was analyzed by constructing a structural equation model, which showed that altitude could exert impacts on EMF through changing functional diversity, with the greatest effect of functional richness on EMF. In conclusion, with the alteration of altitude, the functional diversity may result in changes, thereby affect the SEF and EMF, and the functional diversity is important to maintain the EMF.

Aims Plant diversity is the basis for plant communities to maintain ecosystem stability. Despite the scarcity of vegetation, desert steppes play an irreplaceable ecological service function in terms of wind-break and sand- fixation, etc. However, how plant diversity in desert steppes responds to long-term extreme precipitation changes still remains poorly understood.

Methods Based on a long-term field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural, 30% increase, and 50% increase) conducted in a desert steppe in Ningxia since 2014, the changing characteristics of plant biomass, species diversity and their relationships with soil properties were studied from May to October in 2020.

Important findings During the growing season, plant community biomass, Patrick richness index and Shannon-Wiener diversity index tended to increase first and then decrease, whereas no obvious regularities in Pielou evenness index and Simpson dominance index. Compared with the natural precipitation, the decreased precipitation had less effect on plant biomass and diversity, especially the 30% reduction in precipitation. In most cases, the increased precipitation stimulated the growth of Sophora alopecuroides, Stipa brevifloraand Pennisetum centrasiaticum,and thus increasing plant biomass. However, it did not significantly change plant diversity when precipitation increased, especially the 30% increase of precipitation. Plant biomass was significantly affected by soil urease activity, temperature, water content, pH, phosphatase activity and sucrase activity, while plant diversity was significantly affected by soil water content, electrical conductivity, and urease activity. In general, the results indicated that plants have high adaptability to moderate or even extreme drought in the research area under seven consecutive years of changing precipitation; moderately increasing precipitation increased soil water availability, enhanced exchangeable ion mobility, and stimulated enzyme activity, thereby promoting plant growth. However, the continuous increase of precipitation leaded to the increase of plant biomass and plant water consumption, resulting in the lack of soil water in the late growth season and then the early completion of the life cycle of some plants.

Plant species change soil abiotic and biotic properties which in turn influence the performance of plants, leading to so-called “plant-soil feedbacks” (PSF). It is the prerequisite of plant-soil feedbacks that plant species can cause specific changes in soil microbial communities which are characterized by specialized soil pathogens and mutualists. Specialized microbes can have substantial effects on host plants, but likely do not influence the performance of non-host plants. PSF have been used to interpret ecological processes of different scales since the concept was proposed in the 1990s, such as succession, interspecific competition, biological invasion and effects of global changes on terrestrial ecosystems. In recent years, community ecologists and theoretical ecologists have started to integrate the research of PSF and community ecology, resulting in fundamental progress. In this review paper, we introduce soil microbe-mediated PSF and its implications for plant species coexistence, community structure and ecosystem functions. Classical PSF theory assumes that soil microbes can generate stabilizing process which promotes plant coexistence. However, recent studies show that soil microbes can also cause fitness difference between plant species which can influence species coexistence through equalizing process. Community ecologists predict that rare species have less negative or more positive PSF than abundant species, thereby leading to negative correlations between plant landscape abundance and PSF. However, empirical evidence demonstrates inconsistent patterns such as negative, positive and neutral correlations, and coevolution of plants and soil pathogens is key to reconcile these patterns. Soil microbes are also considered as a fundamental factor regulating succession. Dilution of soil microbial effects is a mechanism of positive plant diversity-productivity relationships. Specialist pathogens and mutualists accumulate in the soil of monocultures, but their negative and positive effects are diluted in multi-species mixtures, thereby increasing and decreasing biodiversity effects on productivity, respectively. We suggest three directions for future studies: empirical testing for specialization of plants and soil microbes, multi-dimensional species coexistence and eco-evolutionary dynamics in plant-soil feedbacks.

Functional biogeography studies the spatio-temporal variations in patterns of traits and functional diversity, their ecological determinants and effects on ecosystem functioning. With the exponential growth in trait data, this field has developed rapidly in the recent decades and made major progress in exploring the response of species distribution, community structure and composition, and ecosystem properties on environmental changes based on traits. In this paper, we reviewed core objectives, historical developments, main research advance and future directions in the field of plant functional biogeography. Traits are the focus of research in functional biogeography. Here, we first described major findings on the spatial patterns of key traits in plant organs (i.e. leaves, stems, roots, and flowers, along with fruits and seeds) to the whole plants, and their relationships with environment, showing that traits variations are the results of plant adaptive evolution and environmental filtering. Secondly, we summarized the indicators of functional diversity, assessed the spatial distributions of functional diversity, and identified their determinants. We also summarized the main data sources of traits and related gap-filling approaches. Next, we reviewed trait associations and trade-offs among and within organs as well as in the entire plants, focusing on the global leaf economics spectrums and wood economics spectrum, and pointing out the strategies of plants to obtain and allocate important resource (i.e. carbon, nutrients and water). We summarized how trait-based approaches help to predict species distribution, and the link between trait diversity with ecosystem functions. We highlighted the challenges in current research and emphasized the importance to focus on the coordination and trade-offs among multiple traits along with both inter- and intra-specific trait variation in future research, transferring species-based models to individual-based ones, and to adopt approaches like trait networks to quantify the links among traits and their response to environmental changes, further to explore adaptation of plants across scales. Meanwhile, we suggested potential improvement in application of current research advances, which may be useful in constructing next-generation vegetation models and guiding the function-based conservation of plant diversity in future research.

Aims To further understand how community functional diversity drives biomass change following nitrogen (N) addition, a nitrogen addition experiment was conducted in an alpine grassland.

Methods Species composition of community and six functional traits of common species were measured in a short-term N addition experiment in Bayanbulak alpine grassland of Tianshan Mountains. We compared the response patterns of species diversity, functional diversity, and community level traits, and quantified the relative contribution of those factors to community biomass variation.

Important findings Both aboveground and belowground biomass increased following short-term N addition, with higher proportional enhancement of aboveground biomass. N addition reduced functional diversity, but did not affect species diversity. At the community level, height and leaf carbon content increased following N addition, whereas specific leaf area, seed mass, and leaf phosphorus content decreased. The variations of species diversity contributed less to the variations of community biomass change, whereas functional diversity and community level traits explained most of the variation of community biomass. Our results support the mass ratio hypothesis. In conclusion, community level functional traits and functional diversity were sensitive to short-term N addition, and played a key role in driving community biomass.

Leaf is one of the important organs of plants that facilitates the exchange of water and air with the surrounding environment. The morphological variation of leaves directly affect the physiological and biochemical processes of plants, which also reflects the adaptive strategies of plants to obtain resources. By focusing on several leaf morphological traits, including leaf size, leaf shape, leaf margin (with or without teeth) and leaf type (i.e. single vs. compound leaf), here, we reviewed the relevant research progresses in this field. We summarized the ecological functions of leaf morphological traits, identified their geographical distribution patterns, and explored the underlying environmental drivers, potential ecological interactions, and their effects on ecosystem functioning. We found that the current studies exploring the distribution and determinants of leaf size and leaf margin states mainly focused on single or specific taxon in local regions. Studies have also explored the genetic mechanisms of leaf morphology development. Leaf traits trade off with other functional traits, and their spatial variation is driven by both temperature and water availability. Leaf morphological traits, especially leaf size, influence water and nutrient cycling, reflect the response of communities to climate change, and can be scaled up to predict ecosystem primary productivity. Further studies should pay attention to combine new approaches to obtain unbiased data with high coverage, to explore the long-term adaptive evolution of leaf morphology, and to generalize the scaling in leaf morphology and its effect on ecosystem functioning. Leaf provides an important perspective to understand how plants respond and adapt to environmental changes. Studying leaf morphological traits provides insight into species fitness, community dynamics and ecosystem functioning, and also improves our understanding of the research progresses made in related fields, including plant community ecology and functional biogeography.

Comprehensively understanding the mechanisms underlying the formation of ecosystem services is a prerequisite for maintaining the sustainable supply of ecosystem services. Plant functional traits directly participate in a variety of ecosystem processes, which in turn affect the supply of ecosystem services. Revealing the relationship between plant functional traits and ecosystem services is an important way to understand the formation mechanism of ecosystem services. Based on a systematic literature review, 86 papers on plant functional properties and ecosystem services were retrieved in the Web of Science database, and data for 466 pairs of plant functional traits and ecosystem services and 83 plant functional traits were collected. The current status of research on the relationship between plant functional traits and ecosystem services was revealed. Moreover, the main plant functional traits that affect different ecosystem services and their mechanisms underlying their impacts were also demonstrated. The results show that the research on the relationship between plant functional traits and ecosystem services mostly focuses on natural ecosystems such as grasslands and forests. Most of these studies focus on ecosystem products providing and supporting services, including biomass, net primary productivity, and soil fertility. Based on the impacts of plant functional traits on different ecosystem services, the plant functional traits can be clustered into five categories: soil-conservation-related traits, water-cycle-related traits, ecosystem- multifunction- related traits, product-providing-related traits, and pollination-biocontrol-related traits. The impacts of climate change, human activities, and variations in spatial and temporal scales on the relationship between plant functional traits and ecosystem services need to be further explored.

The stability of ecosystems determines whether they can sustainably provide key functions and services in the background of global changes. Ecosystem stability, particularly its relation with biodiversity, is one of the central issues in ecology. Whether biodiversity enhances or impairs ecosystem stability has historically aroused much debate. Based on early reviews and studies on different aspects of stability, here we summarized recent advances from three aspects. Firstly, several recent theoretical studies offered novel insights in understanding the multi- dimensionality of stability and the intrinsic link between different stability measures, and we provided an overview on these new insights. Secondly, we reviewed recent empirical and theoretical studies on biodiversity- stability relationships, including those in the context of multidimensional stability. Thirdly, we introduced the recently developed multi-scale stability framework, which provides new opportunity to understand the scaling of stability and extend diversity-stability relations to a multi-scale context. We ended with a discussion on future research questions and directions.

Global change has exerted profound impacts on ecosystem function, such as variations in plant productivity and imbalances in nutrient cycling. Previous studies mostly focused on the impacts of global change on individual functions. However, ecosystems have multiple functions, known as ecosystem multifunctionality (EMF), such that the evaluation based on a single functionality is inappropriate to reflect the overall performance of ecosystems due to the occurrence of trade-offs or synergies among the differential functions. This imposes limitation to our understanding of the effects of global change on ecosystems. Since the initial quantitative study of EMF by Hector and Bagchi in 2007, this field of research has undergone rapid development and the environmental impacts on EMF have received wide attention with intensification of global change. In order to gain systematic understanding of the progress in EMF studies, we conducted a bibliometric analysis for the period 2007-2020 based on CNKI and ISI Web of Science databases. This paper provides a brief description of the development in EMF research and summary of studies concerning the impacts of land use change, warming, changes in precipitation, and nitrogen deposition on EMF. We raised six issues of further attention in future studies of EMF in the context of global change, including (1) requirement of consensus in EMF indices and evaluation method; (2) consideration on the interactive effects among different factors on EMF; (3) elucidation of EMF responses to global change across various temporal scales; (4) understanding of the relationships between multi-dimensional, multi-scale biodiversity and EMF; (5) understanding of the relationships between multiple trophic diversity and EMF; and (6) understanding of the relationships between root functional traits and EMF.

Over the recent decade, biodiversity and ecosystem multifunctionality (BEMF) has aroused as an emerging reserach hotspot in the filed of biodiversity and ecosystem functioning. Ecosystem multifunctionality is defined as the capacity of an ecosystem to provide multiple ecosystem functions simulateneously, it has received broad consideration by community and ecosystem ecologists. In this study, we first conducted a literature review of the research history in biodiversity and ecosystem multifunctionality. Next, we summarized the major trends in biodiversity and ecosystem multifunctionality research including the impacts of biodiversity dimensions, global change drivers and spatial-temporal scales on ecosystem multifunctionality. We reviewed the new research methods and research directions emerged in the field. We also defined a new concept, i.e., ecosystem multiserviceability (EMS) based on the distinction between ecosystem functions and ecosystem services. Finally, we briefly summarized the limitations in current research of biodiversity and ecosystem multifunctionality/multiserviceability (BEMF/BEMS) and presented the outlook for future study.

Under intensifying human activities and climate change, spatiotemporal changes in ecosystem composition and structure are becoming increasingly drastic and intricate, and there are trends of degradation in many ecosystems. An improved understanding of ecosystem dynamics and their underlying mechanisms in the context of global change can not only help resolve fundamental theoretical questions in ecology, but can also inform applied issues in ecosystem restoration and conservation. Here, we review different models of ecosystem dynamics (gradual continuum, threshold/regime shift, and stochastic) and conceptualize the mechanisms by which biotic interactions can potentially modulate ecosystem dynamics. We then synthesize the state of understanding how biotic interactions regulate secondary succession, regime shift, and species range shift—ecosystem dynamics subject to intense recent investigation. We further discuss results from studies that applied theories on biotic interactions in ecosystem restoration and conservation. We show that there is a growing body of research revealing 1) that multiple types of biotic interactions, such as competition, facilitation (including mutualism), and trophic interactions, can drive or substantially alter the patterns, directions, and rates of ecosystem change at various spatiotemporal scales, and 2) that managing biotic interactions is likely to greatly enhance the performance of ecosystem restoration and conservation. To move forward, we highlight that further research is needed to better understand how the impacts of biotic interactions on ecosystem dynamics vary spatially and temporally, how biotic interactions modulate ecosystem dynamics under multiple anthropogenic disturbances, and how best to manage biotic interactions to optimize ecosystem conservation and restoration.

The food web sustains its structure mainly by bottom-up and top-down regulations of the species interactions among different trophic levels. However, global changes can alter interspecific relationships and threaten the maintenance of biodiversity. It is still unclear how global change alters the structure of the food webs. In recent years, based on numerous studies on food webs composed of multi-trophic levels at large spatiotemporal scales, researchers have found that global changes alter food web structure mainly through three mechanisms: phenological mismatching, loss of key species and biological invasion. Here we focused on these three mechanisms and reviewed how these mechanisms regulate food web structure change, with further discussions on the driving factors in ecology and evolution. All these three mechanisms can alter the interspecific interactions, resulting in distortion of the regulation of food webs. The major difference among these three mechanisms is how interspecific interactions are changed. Phenological mismatching occurs due to the asynchronous responses in the phenology of different species to global changes, while the loss of key species can change or even entirely destroy some critical feeding/predation relationships, and invasive species often simplify the food web structure by causing strong interspecific competition to exclude species at the same trophic level. Finally, we pointed out that the changes in food web structure actually depend on the adaptation of species to the ongoing global changes and we further provided some insights into future research directions. With aggravated global change impacts, it is necessary to further study the mechanisms underlying how global changes influence food web structure, to reinforce the extant theoretical basis for formulating biodiversity conservation and ecological restoration measures.

Varied species interactions form complex species interaction networks in diverse ecological communities. Understanding how the network structure affects ecosystem functions and community stability is one major issue for community ecology. Species interactions can directly affect the flow and circulation of matter and energy among different components of ecosystems. As a result, the network structure is closely related to the structure, stability, and functioning of ecological communities. Prior studies on interaction networks have shed light on community assembly, biodiversity maintenance, ecosystem stability, coevolution and trait diversification. Currently, biodiversity and ecosystem functions have been largely affected by global environmental changes. The interaction networks and their relationship with biodiversity loss in a changing world have become important research topics. Exploring the structure and assembly of species interaction networks, stability, and ecosystem functions is significant for understanding the maintenance mechanism and biodiversity conservation. Here, we reviewed the research advances in the structure of ecological networks and their determinants, network stability, the relationship between network and ecosystem functions, and the mechanisms underlying these relationships. We also suggest future research directions on how to apply machine learning and multilayer network to disentangle the effects of environmental change on network structure and ecosystem functions by integrated theoretical and empirical studies.

Plant-herbivore interaction is one of the most common and important interspecific relationships in nature, which is the core and foundation of the food web theory. In this paper, we review the effects of herbivores on the characteristics of plant individuals, populations and communities, as well as the defense strategies and mechanisms of plants against herbivores at the levels of individuals, populations and communities. Herbivory can significantly change the growth, reproduction and survival rates of plant individuals and populations, which can in turn affect the composition and diversity of plant communities. In order to defend against herbivory, plants have evolved a series of defense mechanisms at the individual, population and community levels. At the individual and population levels, plants avoid herbivory mainly by chemical and physical defense. At the community level, however, plant defenses are achieved mainly by their influences on the behaviors of herbivores. This paper then introduces and compares important hypotheses and theories in related fields. Finally, we point out major existing research issues and identify possible future research directions. Given that natural systems are experiencing strong disturbances from human activities and climate changes, exploring how these disturbances affect plant-animal interactions, and how these changes in plant-animal interactions feedback on the structure, function and stability of the ecosystems, will not only have important theoretical significance, but also help us to formulate successful ecosystem management policy in the future.

Aims In recent years, under the background of climate change and human activities, the trend of biodiversity loss is increasing. Such accelerated loss in biodiversity could bring serious consequences to ecosystem functions. At present, the research on ecosystem function ignores the important driving role of carbon and nitrogen cycling in soil and microorganism on the above ground ecosystem functions. Any changes of soil carbon, nitrogen and microorganism may affect the ability of belowground community, which can have substantial effects on the aboveground ecosystem functions. Our aim was to explore the driving factors and key mechanism of abovegroud ecosystem functions (AEF) in alpine grassland.
Methods From July to August 2015, we conducted a transect survey in alpine grasslands to measure plant community and soil properties across Qingzang Plateau. There were in total 115 sample sites. The aboveground ecosystem function was calculated based on the aboveground biomass, leaf carbon, leaf nitrogen and leaf phosphorus. The effects of key elements such as soil organic carbon, total nitrogen and biomass on the aboveground ecosystem function were analyzed. Combined with mean annual precipitation and air temperature, we explored important drivers of AEF and related mechanisms.
Important findings Precipitation has a greater impact on aboveground ecosystem functions, while air temperature has a minor impact. Mean annual precipitation, soil microbial nitrogen content and aridity index had relative higher importance to aboveground ecosystem functions. Specificially, mean annual precipitation, soil microbial nitrogen content and aridity index accounted for the variations of 21.1%, 10.9% and 10.1%, respectively. The findings indicated that soil properties might play more important roles than plant community and productivity to aboveground ecosystem functions. Considering the cascading impacts of climate factors on soil nutrients cycling and microorganisms, soil microbial biomass nitrogen content plays an important role in regulating AEF of alpine grassland, Qingzang Plateau.

Aims This study demonstrates the consistencies and discrepancies of correlations between climate factors and normalized difference vegetation index (NDVI) in the Protected Zones for Ecological Functions (EFPZs) in China, which provide useful information for monitoring in subsequent studies of vegetation dynamics.
Methods Based on the MODISNDVI data and the grid data for monthly precipitation and air temperatures from 2000 to 2015, the dynamics of NDVI and correlations with climatic factors were examined across 46 EFPZs at two spatial scales, by individual EFPZs and the pixels, using linear tendency and partial correlation methods. In accordance to the analyses, the EFPZs were categorized into different types of climatic influences.
Important findings The overall NDVI across the EFPZs showed an increasing trend, with the average linear slope of 0.045·a^-1. Pixel scale analysis showed that NDVIincreased significantly in the central regions and the northeast of China. Partial correlation coefficients between NDVI and precipitation in the EFPZs varied between -0.30 to 0.72, and were positive for 32 in the EFPZs. Partial correlation between NDVI and air temperature ranged from -0.36 to 0.92, with positive correlations in 39 in the EFPZs. In 50.6% of the pixels, NDVIwas positively correlated with precipitation, mainly in northeast and northwest China. In 64.6% of the pixels,NDVI was positively correlated with air temperatures, mainly in the northeastern and the northern edge of the Qingzang Plateau. Strong temperature-precipitation driving is the main type of climatic influences on NDVI changes across the EFPZs, accounting for 38.7% of the total, with temperature driving type being secondary, accounting for 27.3%; non-climatic driving type accounts for 17.6%. Our results show the NDVI in the EFPZs are significantly correlated with climatic factors concerning precipitation and air temperatures, and that NDVI dynamics in 82.4% of the areas are driven by climate factors. Studying the changes in NDVI and the responses of NDVI to climate factors is very important for understanding the dynamics of vegetation in the EFPZs under climate warming.

Aims The Pinus thunbergii communities is widespread across islands in both Yellow Sea and East China Sea. The objective of this study is to examine the latitudinal pattern of functional diversity and abiotic and biotic drivers of P. thunbergii communities. Our aims are to advance understanding of whether the zonal character of latitude oriented pattern of biodiversity still holds in the same community type across the highly isolated and fragmented landscape.
Methods We investigated community structure and measured plant functional traits across 60 P. thunbergii communities in 27 islands, spanning 13 degree in latitudes of Eastern China. Linear regression was used to analyze the relationships between functional diversity of the P. thunbergii community and each of the biotic factors (the dominance of P. thunbergii and species diversity) and abiotic factors (annual mean temperature, total solar radiation and aridity index). The relative importance of abiotic and biotic factors on the functional diversity of P. thunbergii communities was determined by using the generalized linear model and variance decomposition.
Important findings With the increasing latitude, the dominance of P. thunbergii,species richness, and functional richness, functional dispersion and Rao's quadratic entropy (RaoQ) of stem traits alone and stem and leaf traits in combination decreased significantly but those of leaf traits did not show clear trend, across P. thunbergii communities. The dominance of P. thunbergii, species richness and climatic factors jointly explained 63%, 47% and 39% of variation in each of functional richness, functional dispersion and RaoQ of the combination of leaf and stem traits, and 56%, 67% and 53% of variation in each of functional richness, functional dispersion and RaoQ of stem traits, but small variations in leaf traits (21%-30%). Species richness and Simpson diversity significantly increased but Shannon-Wiener diversity significantly decreased leaf functional richness. Aridity significantly increased functional diversity of stem traits and the combination of leaf and stem traits. Annual mean temperature significantly decreased functional dispersion and RaoQ of wood traits. These results indicate that there is a clear latitudinal pattern of functional diversity in P. thunbergii communities across islands. Climate and species richness play the key roles for shaping the latitudinal variations in functional diversity of P. thunbergii communities across islands in Eastern China.

The response and feedback of ecosystems to global change is a scientific frontier in ecosystem ecology, which combines macro- and micro-level studies across multidisciplines. It focuses on the responses of ecosystem structure and function to global change, and its objective is to achieve sustainable use of ecosystem services. Based on the review of previous studies, we summarized the major progress and main achievements in this field and made an outlook for future challenges. According to the research content and object, this special issue systematically reviewed the effects of different global change factors, including increasing atmospheric CO₂ and O₃ concentration, global warming, precipitation change, increasing nitrogen deposition and land use change, on terrestrial plant ecophysiology, community structure, and ecosystem functions, and global change impacts on marine ecosystems. It mainly discussed the changes in biogeochemical cycles and biodiversity under global change, and clarified the mechanisms underlying feedback between ecosystem and climate change. The study of this research area could provide theoretical basis for the construction of global change adaptation strategies.

Aims Shrub encroachment is a critical ecological problem in arid and semi-arid ecosystems worldwide. The effects of shrub encroachment on ecosystem structure and function of grasslands are complicated and need to be explored in future studies. Our objective is to examine the effects and pathways of shrub encroachment on ecosystem structure and function in a typical steppe of the Inner Mongolia grassland.
Methods Three grassland sites with different degrees of shrub encroachment (i.e. light, moderate, heavy) were selected in the Xilingol Nei Mongol, of which Caragana microphylla was the dominant shrub. Species richness and composition, aboveground net primary productivity (ANPP), soil property, and plant functional traits of dominant species were determined in this study. In addition, species diversity, functional attribute diversity, community-weighted mean traits, and vegetation leaf and soil carbon and nitrogen pools were further calculated.
Important findings 1) The species richness, functional attribute diversity and community-weighted mean traits differed significantly among three grassland sites, and species diversity and functional diversity were relatively higher in the moderate shrub-encroachment site, indicating moderate shrub-encroachment favors biodiversity maintenance. 2) The aboveground net primary productivity of heavy shrub-encroachment grassland was significantly higher than those of light and moderate shrub-encroachment grasslands, which was mainly due to a shift in functional group composition, that is, the proportion of annuals and biennials to perennial grasses and forbs increased greatly with intensifying shrub encroachment. The vegetation leaf and soil carbon and nitrogen pools differed little among three sites. 3) Shrub encroachment did not directly affect ecosystem function, including ANPP, vegetation and soil nutrient pools, but it indirectly affected them through pathways of the shift in functional group composition and changes in soil property and functional diversity. Particularly, the shift in functional group composition and intensified soil drought and basification was separately important biotic and abiotic factors for variations in ecosystem function.

Aims The Nei Mongol Steppe plays an important role for livestock production, and it has been one of the green ecological shelters for Northern China. Enhancing some ecosystem services (provisioning services) in managing the ecosystems may causes reductions of other services, such as regulating and supporting services. The knowledge on how grazing intensity influence the trade-offs is lacking. Methods In order to find out the optimized grazing regimes, we conducted an experiment on a typical steppe in Xinlin Gol with four grazing intensities (no grazing, light grazing, moderate grazing and heavy grazing) in the Nei Mongol Steppe. Important findings Our results showed that: synergetic, trade-offs and no relationships among different ecosystem services existed in all treatments on the managed steppe system. The trade-offs relationship was found between soil respiration rate and net plant biomass growth, and between biodiversity and net photosynthetic rate. However the synergetic relationships were observed between net plant biomass growth and soil water content, between net plant growth biomass and net photosynthetic rate, and also between grassland evapotranspiration rate and biodiversity. The results indicated soil organic carbon was not related to other ecosystem services and functions. Grazing could weaken the conflicts among the ecosystem services. Moderate grazing intensity maximumize ecosystem services and functions.

The loss of genetic diversity is accelerating due to habitat loss and population reduction caused by global change and anthropologenic activities. For species-poor ecosystems, the effect of genetic diversity on ecosystem functioning may not be smaller than that of species diversity. Therefore, understanding the relationship between genetic diversity and ecosystem functioning (GD-EF) and its underlying mechanisms is important for biodiversity conservation, responses of ecosystems to environmental change and ecological restoration. Here, we reviewed the studies on the effects of plant genetic diversity on ecosystem structures (community structure of the higher tropic level) and ecosystem functions (primary production, nutrient cycling and ecosystem stability), and the mechanisms underlying these relationships. We also discussed the influence of functional diversity on GD-EF, the comparison of effects of the genetic and species diversity on ecosystem functioning, and the application of GD-EF in the ecological restorations. We finally pointed out the limitations in current studies to provide references for the future: (1) further studies on the mechanisms of GD-EF are needed; (2) no study has evaluated the influence of genetic diversity on maltifunctinarity; (3) the impacts of different measurements of genetic diversity on ecosystem functioning are unclear; (4) there are lack of long-time GD-EF studies and GD-EF studies conducted at multidimensional scales; (5) the relative importance of genetic diversity and other factors on ecosystem functioning in the nature is unclear.

With increasing data availability in the big data era, many traditional statistical analyses based on the mean or median are insufficient or inappropriate to elucidate the complex patterns of variation. This is particularly the case when multiple factors are involved and the bivariate scatter occurs as scatter clouds. In such circumstances, constraint line (or envelope) method could be an alternative and effective tool to extract the data boundaries, thus improves our understanding of the complex relationships between limiting factor and response factor. Here, we synthesize the major findings and achievements in the field of applying the constraint line method in ecology. Specifically, we first describe the history and development of the constraint line method. We then discuss the techniques to establish the constraint lines with examples, and discuss the applications and implications of the constraint lines in species distribution, population performance, and optimization problem. We suggest simultaneously application of both constraint lines and regression techniques to the same datasets to achieve a comprehensive understanding of ecological process and underlying mechanisms. Such combined methods should be used with special attention to the role of spatial heterogeneity and scale dependency. We also discuss in detail the potential applicability of the constraint line method in studying the linkages between ecosystem services, and land system design.

Aims Over the past twenty years, most biodiversity and ecosystem functioning (BEF) research has focused on the effects of species diversity on single or just a few ecosystem functions. However, ecosystems are primarily valued for their ability to maintain multiple functions and services simultaneously (i.e. multifunctionality here- after). This paper first introduced the constantly perfected concept of “multifunctionality”, and then tried to make some modifications to the current mainstream quantitative method in order to evaluate the multifunctionality of grassland communities with the management of clipping, enclosure and grazing in Inner Mongolia, investigating the relationship between the multifunctionality and species diversity. Methods In free grazing grassland, four sites were set and each site was divided into two parts to conduct enclosure and clipping management respectively. After seven years, 15 quadrats (1 m × 1 m) were established for each type of management in each site (total 60 quadrats for each type) using the regular arrangement method; as a control, we also established 20 quadrats (two sites) in grazing grassland. For each quadrat, we carried out plants census and collected soil mixture sample, measuring 16 soil variables, and then calculated the biodiversity indices and multifunctionality index (M-index) by means of factor analysis. Important findings The results showed that M-indexes by the two evaluation methods were strongly correlated at both quadrat and site scale, suggesting that our modified method was reliable. Over-grazed communities had the lowest biodiversity indices and their most soil indicators were also low, showing obvious degradation features. Enclosure and clipping communities (seven years) had higher biodiversity and better soil indicators. The rank of M-indexes was clipping community (0.2178) > enclosure community (0.0704) > grazing community (-0.8031). The vegetation was distributed mainly along the gradients of water and fertility. Among the biodiversity indices, evenness (Pielou) index and richness (Margelf) index were most strongly correlated with multifunctionality, and their explanatory power (R²) for M-index were higher at site scale (R² = 0.5921, p = 0.0093; R² = 0.7499, p = 0.0007) than at quadrat scale (R² = 0.1871, p < 0.0001; R² = 0.1601, p < 0.0001), indicating study scale played an important role in the determinants of multifunctionality. At both quadrat and site scales, M-indexes is a linear positive function with species evenness and a hump-shaped function of species richness. Therefore, in contrast to enclosure, clipping was more conducive to maintain the ecosystem multifunctionality in this region, and the ecosystem with moderate specie richness, where these species are evenly distributed might have better multifunctionality.

The concept of ecological thresholds was raised in the 1970s. However, it was subsequently given different definitions and interpretations depending on research fields or disciplines. For most scientists, ecological thresholds refer to the points or zones that link abrupt changes between alternative stable states of an ecosystem. The measurement and quantification of ecological thresholds have great theoretical and practical significance in ecological research for clarifying the structure and function of ecosystems, for planning sustainable development modes, and for delimiting ecological red lines in managing the ecosystems of a region. By reviewing the existing concepts and classifications of ecological thresholds, we propose a new concept and definition at two different levels: the ecological threshold points, i.e. the turning points of quantitative changes to qualitative changes, which can be considered as ecological red lines; the ecological threshold zones, i.e. the regime shifts of the quantitative changes among different stable states, which can be considered as the yellow and/or orange warning boundaries of the gradual ecological changes. The yellow thresholds mean that an ecosystem can return to a stable state by its self-adjustment, the orange thresholds indicate that the ecosystem will stay in the equilibrium state after interference factors being removed, whereas the red thresholds, as the critical threshold points, indicate that the ecosystem will undergo irreversible degradation or even collapse beyond those points. We also summarizes two types of popular Methods in determining ecological thresholds: statistical analysis and modeling based on data of field observations. The applications of ecological thresholds in ecosystem service, biodiversity conservation and ecosystem management research are also reviewed. Future research on ecological thresholds should focus on the following aspects: (1) methodological development for measurement and quantification of ecological thresholds; (2) emphasizing the scaling effect of ecological thresholds and establishment of national-scale observation system and network; and (3) implementation of ecological thresholds as early warning tools in ecosystem management and delimiting ecological red lines.

Examining the drivers and regulating mechanisms of multiple ecosystem services has emerged as a central issue in ecology in recent years. In this paper, we start with the definition of ecosystem services, recent progresses and research priorities in the field. Then, we propose an experimental network to examine the key drivers of ecosystem services and relationships among multiple ecosystem services across grassland and desert ecosystems in northern China. The research network include conceptual diagram, research questions and objectives, field experimental design, ecosystem properties and processes observed across four grassland and desert sites. We review the major findings from the experimental network and future research directions in grassland and desert ecosystem services.

Ecosystem with alternative stable states would respond abruptly to minor changes in the external conditions and switch into an alternative stable state with different ecosystem structures and functions when the system approaches the transition threshold. This phenomenon is called critical transition. It is often the case that such transition can result in marked changes in ecosystem services, which are much likely to impact the sustainable development of human being. It is difficult to predict the critical transitions in ecosystems, but the large amount of research in this field show that by monitoring some generic properties (i.e. early-warning signals) relating to ecosystem status, we are able to discern if the system approaches the transition threshold; this can be used to predict the critical transitions in ecosystems. This paper summarizes the major findings and achievements in the field of detecting critical transitions in ecosystems. It first discusses the mechanism and consequence of critical transitions, and then introduces the basic theory behind the early-warning signals. We sum up the methods used to extract early-warning signals both from temporal and spatial dimensions. Finally, challenges confronting the contemporary research are summarized. In future, the application of early-warning signals should make full use of both temporal and spatial data and combine different indicators to improve our ability to forecast unfavorable environmental events. Also, special attention needs to be paid to the relationship between critical transitions and ecosystem structures so that we can strengthen the ability to predict critical transitions in ecosystems.

Aims The relationship between biodiversity and ecosystem functioning has been a central issue in ecology. However, this relationship is poorly understood for the Stipa breviflora grassland, which is a major community type of desert steppe in Nei Mongol. With unpredictably fluctuating climate conditions, these desert steppe ecosystems are fragile and provide a unique opportunity to test our current understanding of the relationship between biodiversity and ecosystem functioning. This study has two objectives: (1) to examine if species diversity and functional group diversity affect ecosystem primary productivity in the desert steppe of Nei Mongol and (2) to explore how resource supply levels affect the relationship between diversity and productivity.
Methods Based on life forms, species were classified into five functional groups: shrub and semishrub, perennial bunchgrass, perennial rhizome grass, perennial forb, and annual and biennial. Species richness and functional group richness were used to represent species diversity and functional group diversity, respectively. Based on the dryness coefficient, 202 sites across the S. breviflora grassland in Nei Mongol were sampled, and divided into two resource supply levels: arid and semiarid zones. In order to tease out the effect of precipitation, partial regression analysis and partial correlation analysis were used for exploring the relationship of ecosystem primary productivity to species richness and functional group richness, respectively. According to the determination coefficient of regression analysis, the effect of resource supply levels on the diversity-productivity relationship was evaluated.
Important findings Species richness and ecosystem primary productivity were both positively and linearly correlated with precipitation, but no significant correlation was found between functional group richness and precipitation. Ecosystem primary productivity increased significantly with species richness, but not with functional group richness. Resource supply levels could affect the diversity-productivity relationship in that plant species diversity generally had a weaker effect on ecosystem primary productivity at the lower resource supply level and a stronger effect at the higher resource supply level.

Aims Recent theoretical and empirical work suggests that species diversity enhances the primary productivity and stability of communities. However, the relationships between the diversity of different species types (i.e., total species, response species, effect species and common species), the special function of ecosystems, and the potential mechanism driving stability remain unclear. Our objective is to address the question by comparing the diversity effect of these different types on aboveground net primary productivity (ANPP) and community stability.
Methods Our experiment was conducted in alpine meadow at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2011. We used a split-plot design with clipping treatment in the whole plot using three clipping levels (stubbled 1 cm, 3 cm and unclipped). Subplots were treated with fertilizer (urea 7.5 g·m^-2·a^-1+ ammonium phosphate 1.8 g·m^-2·a^-1 and unfertilized) and watering (20.1 kg·m^-2·a^-1 and unwatered).
Important findings We observed that the diversity of different species types affected ecosystem functioning differently. ANPP was mainly affected by the diversity of response species and effect species, whereas community stability was largely affected by that of common species. The maintenance of stability depended on increasing diversity in common species, and the potential mechanism was the portfolio effect. Both the over-yielding effect and asynchrony effect, however, had no influence on stabilizing the community. Clipping had enormous effects on the diversity of total species, whereas the changes in diversity of response species mainly connected with resource availability. Thus, clipping and fertilization had reverse effects on species diversity, ANPP and stability, i.e., the former increased both species diversity and stability and decreased ANPP, while the latter had opposite effects on them. Our results suggest that ANPP is driven by the diversity of a few effect species because they have a great influence on ANPP, while stability is driven by the diversity of a large number of common species because they can coexist stably in the community. The portfolio effect is the main mechanism of the diversity-stability relationship. The diversity effect of different species differs among each other; therefore, in terms of specific ecosystem functioning, we infer that “functional identity” of species in community is more important than diversity per se and it may be incorrect if we did not discriminate when defining the relationship between species diversity and ecosystem function in any situation.

Functional traits influence ecosystem services through their effects on ecosystem attributes, processes and their maintenance. Research on the relationship between functional diversity and ecosystem function can contribute to investigating the mechanism of ecosystem functioning and services supplied, which provides insight on ecosystem services. This study reviewed research on functional traits and framework of ecosystem services, relationship between functional diversity and ecosystem function and application of functional traits in ecosystem services. We proposed a framework of ecosystem services based on functional traits. First, abiotic factors and functional diversity indices that significantly affected ecosystem function should be investigated. Second, (a) quantitative relationships between abiotic factors and functional indices and ecosystem function and (b) quantitative relationships between ecosystem function and ecosystem services should be developed. Third, quantitative relationships between functional diversity and ecosystem services should be constructed. At the same time, community assembly theory and species co-existence mechanism should be incorporated into the investigation of the mechanism relationship between functional diversity and ecosystem function to analyze the mechanism of formation and variation of ecosystem services. The results of ecosystem services based on functional traits can support a scientific basis for the process of decision-making in ecosystem management.

The concept of ecosystem services was first used in 1960s in abroad and the terminology of “ecosystem services” appeared in 1981. Three classifications of ecosystem services included function classification, structure classification and description classification, in which function classification has been used widely. The relationship between ecosystem services and biodiversity was examined to understand the mechanism of formation and variation in ecosystem services. At present, many case studies have been conducted to obtain the economic values of ecosystem services at local, river basin, regional and national levels with three kinds of methods: economic method, emergy method and benefit transfer. In China, the concept of ecosystem services was introduced in 1990s and, since then, there have been many studies about ecosystem services which involves the introduction of abroad studies, forming and accumulating process of ecosystem services and case studies.

Because of limitations on the studies of ecosystem services, including the reliability of the evaluation results, confusion of ecological capital and ecosystem services, uncertainty of the quantity of ecosystem services, uncertainty of the monetary values of ecosystem services, and complexity of ecosystem functions and services. A new paradigm of ecosystem services should be set to strictly distinguish the ecosystem services from ecological capital, to evaluate the ecosystem services on the basis of ecological monitoring and ecological models, and to divide the region into different units in evaluation of regional ecosystem services. The researches on ecosystem services should pay more attention in the complex relationships between ecosystem services, structure and processes, the response and feedback of ecosystem services to human activities, the impacts of changes in ecosystem services on human well_being, the impacts of policies and institutions on ecosystem services, and the monetary values of ecosystem services from different kinds of ecosystems.