Plant ecological stoichiometry, as a branch of ecological stoichiometry, focuses on the study of elemental content, ratios and relationships within and across plant organs, and the underlying biotic and abiotic drivers. In the 19th century, chemists detected the elemental contents in plant organs via laboratory experiments, sprouting the exploration of plant stoichiometric characteristics. Nowadays, ecologists have explored plant ecological stoichiometric characteristics and their responses to global changes and relationships with plant functional traits, using both field investigation and manipulative experiments. These sustained efforts have largely enriched the knowledge and understanding of plant ecological stoichiometry. In this paper, we briefly introduced the history and reviewed the research progresses of plant stoichiometry since the 19th century. Firstly, we proposed the developmental history of plant ecological stoichiometry as three main periods: sprouting, hypothesis foundation, and theoretical construction periods, and introduced some representative works for each period. Secondly, we overviewed plant ecological stoichiometric characteristics across organs, life forms and environmental gradients. The geometric mean values of leaf nitrogen (N) and phosphorus (P) contents and N:P mass ratios in global terrestrial plants are 18.74 mg∙g^-1, 1.21 mg∙g^-1 and 15.55 (i.e. similar to the Redfield ratio of 16:1), respectively. Leaf N and P contents at either species or community level generally show a decreasing trend with increasing temperature and precipitation, and have large variations among life forms, with higher values in herbaceous than woody plants, and deciduous broad-leaved than evergreen broad-leaved and coniferous woody plants. Compared with leaves, the stoichiometric characteristics of fine roots and other organs in plants remain poorly documented. Thirdly, we reviewed the effects of nutrient addition on plant ecological stoichiometric characteristics. In general, N addition increases soil N availability, then the N content and N:P in plants, thus leading to an increase in plant productivity to some extents. P addition might alleviate the N and P imbalance induced by excessive N inputs, and then increase plant P content. However, long-term nutrient fertilization could perturb the intrinsic stoichiometric characteristics in plants, resulting in the deteriorated nutrient imbalance in tissues and then the subsequent decline in plant productivity. Fourthly, we introduced the main hypotheses of plant ecological stoichiometry. These hypotheses include function-associated hypotheses, environment-associated hypotheses and evolution-associated hypotheses, which delineate the relationships of stoichiometric characteristics with plant growth functions, environmental factors and plant evolutionary history, respectively. Finally, we made an outlook on future research in the area of plant ecological stoichiometry, and highlighted ten potential and important research themes.

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.

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.

In this article, I first briefly introduce the concept of “Carbon Neutrality”, and then discuss the vital role of ecosystem carbon sinks in achieving the carbon neutrality target. It is assertive that any efforts to achieve the carbon neutrality target depend unavoidably on both reducing carbon emissions and enhancing carbon sequestrations. There are four key factors in reducing carbon emissions, including lowering energy consumption in human activities, restructuring fossil energy consumptions especially decreasing coal consumption, promoting energy use efficiency, and developing clean and low-carbon energy. Enhancing carbon sequestration relies inclusively on restoration, construction, and better management of the ecosystems. Benefited from enhanced vegetation growth and ecological engineering practice, Chinese terrestrial ecosystem has acted and will continue to act the significant role in the carbon sequestration. To improve the ecosystem carbon sequestration, I propose the “three-optimization principles”, i.e., optimal ecosystem arrangement, optimal species setting, and optimal ecosystem management. In addition, I also state some viewpoints on potential problems and challenges in the “post-carbon neutrality” era. It may be crucial to proactively and rationally think about the possibilities of declining global vegetation productivity and relevant new environmental issues caused by a decrease in the CO₂ concentration rising in the era.

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.

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.

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.

Quantitative estimation of the contribution of predictary variables to community composition is a hotspot in community ecology. However, multicollinearity and joint contributions among predictors make it difficult to estimate the importance of predictor in specific analysis scenarios. To address this issue, the “rdacca.hp” package provides a new quantitative indicator by introducing the concept of hierarchical partitioning (HP) to assign individual effects for individual predictors (or groups of predictors) across all possible model subsets. The package solves the problem of estimating the relative importance of predictors with multicollinearity in canonical analysis. The “rdacca.hp” package has become an important tool for community ecological analysis. To further promote users’ understanding and use of the “rdacca.hp” package, we demonstrate the general steps for using this package in canonical analysis with an example analyzing the important environmental and spatial drivers that shape the oribatid mites (Oribatida) community. Subsequently, we conduct a bibliometric analysis of recent studies using “rdacca.hp” package. The results show that, since its launch, the package has been widely used as a fundamental quantitative framework in ecology, environmental science and related disciplines. Finally, we discuss the further application and extension of the “rdacca.hp” package. In conclusion, this paper aims to advocate the understanding and application of the “rdacca.hp” package for domestic researchers.

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.

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.

Plot-based data are an important foundation for studying plant community characteristics and compiling vegetation monographs, vegetation map, and vegegraphy. It is the key data source of studies in vegetation ecology. To understand the species composition, community characteristics, and distribution pattern of special plateau vegetation on the Qingzang Plateau (QZP), this study uses the data of 338 sites including 758 plots in different regions of the QZP from 2018 to 2021 to analyze the species composition, floristic characteristics, and vegetation classification of plateau plant communities. A plot-based dataset of plant community on the QZP is then established. The 758 plots have 837 plant species belonging to 279 genera from 65 families in the alpine and temperate vegetation communities. The largest number of species are found in five families: Asteraceae (134 species), Poaceae (88 species), Fabaceae (75 species), Rosaceae (43 species), and Cyperaceae (40 species), as well as five genera: Artemisia (29 species), Pedicularis (27 species), Saussurea (25 species), Astragalus (23 species), and Poa (23 species). The floristic composition is mainly temperate (145 genera) and cosmopolitan (36 genera). The growth forms of the species are mainly herbs (83.51%) and shrubs (10.87%), and the life forms of herbs and woody plants are mainly perennial herbs (88.23%) and deciduous shrubs (83.67%), respectively. A total of 338 sites can be divided into four vegetation formation groups, 10 vegetation formations, 20 vegetation subformations, 78 alliance groups, and 117 alliances, in which 34 are steppe alliances, 33 are meadow alliances, 33 are desert alliances, 14 are shrubland alliances, and 3 are coniferous forest alliances. This dataset covers most of the alpine shrubland, meadow, steppe, desert, and temperate steppe, desert vegetation regions of the QZP. This work provides a solid foundation for exploring the vegetation characteristics and regularity of vegetation zonal differentiation and determining the impacts of climate change and human disturbances on alpine vegetation and their ecological restoration. The dataset also provides a reference for the updating of the next generation of China's vegetation map.

Drought-related tree mortality profoundly impacts the ecosystem functions and carbon budgets, in which one of the principal mechanisms involved is the catastrophic failure of the hydraulic systems. However, our understanding of tree hydraulic systems and the mechanisms of tree death under extreme drought conditions are limited because the responses of trees to drought stress are multi-dimensional and complex. In this review, we first expounded the indexes of measuring plant drought resistance, and focused on the stomatal safety margin (SSM) that can be used to comprehensively evaluate the drought tolerance of plants. A larger positive value of SSM indicates a stronger coordination between stomata and hydraulic traits, a lower possibility of xylem embolization, and a more conservative hydraulic strategy adopted. Second, we integrated general response processes of woody plants to drought stress. Third, we introduced response mechanisms of different plant organs (leaf, stem and root) to drought stress. The probability of reaching the critical threshold and the duration of tree death are determined by interactions between physiological and morphological traits. Finally, we discussed hydraulic recovery mechanisms of woody plants, and put forward three research priorities in the future: (1) to improve the methodology for measuring leaf hydraulic conductance, especially the xylem and outside-xylem hydraulic conductance, and quantify the relative contributions of the four water transport pathways in mesophyll tissues; (2) to quantify variations in the epidermal permeability for better understanding plant water-use strategies; and (3) to deepen the understanding of the water-carbon coupling mechanisms, and link individual-level structural and physiological traits with patterns and processes at the community and landscape levels, so as to better assessing and monitoring the potential risk of drought-induced tree mortality.

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 Various colors combined with symbols are usually employed to differentiate vegetation types in vegetation mapping, aiming to convey the vegetation information to readers more visually and clearly. How to differentiate vegetation types by appropriate setting of color and symbol is a key step in vegetation mapping, especially for regions with diverse vegetation types. Usually, vegetation map legends are based on the vegetation classification system. Recently, the vegetation classification system of China has been revised according to the achievements in vegetation surveys and research over the past decade. Therefore, it is necessary to put forward a new color and symbol setting scheme for vegetation mapping. Our objective is to improve the scientificity and artistry of current vegetation mapping.
Methods The principles of color and symbol setting of existing vegetation maps and other thematic maps were summarized. Based on the principles of systematicness, scientificity and symbolism, the changes and combinations of the three color attributes (hue, lightness and saturation) and the basic visual variables (shape, size, direction, color, density and brightness) of the symbols were taken in consideration for the national vegetation map legends. In the legends, Vegetation Formation Groups were differentiated by hues, and Vegetation Formations and Vegetation Subformations were represented by different lightnesses and saturations. In addition, different symbols attached to the colors were employed to distinguish vegetation types. The colors and symbols were designed to reflect the physiognomy and habitats of the vegetation types as much as possible.
Important findings The principles of color and symbol setting for vegetation mapping and a new scheme of national vegetation map legends were presented. These results would provide guideline for vegetation cartographer to set the legends of the new Chinese vegetation map (1:500 000).

Arbuscular mycorrhizal (AM) fungi are a group of soil-dwelling fungi that can form symbiotic associations with most terrestrial plants. The extraradical mycelium can colonize different plant roots in addition to hyphal fusion, thus form extensive arbuscular mycorrhizal networks (AMNs) underground. AMNs can transport and recycle water and nutrients including carbon, nitrogen, phosphorus among plants, recent evidences show that AMNs can also transfer defensive signals to neighboring plants when plants suffer environmental stresses, thus providing early warning to surrounding neighbors. However, the research on AMNs-mediated signal transfer is still in its infancy. Here, we firstly reviewed current research progresses in this research area, then proposed the unanswered questions that worth exploration in the future, including the possible pathways and mechanisms of signal transfer via AMNs among plants, the possible regulation of mycorrhizal symbionts by AMNs-mediated signal transfer, and the common techniques and their development used in the study of AMNs. Finally, we discussed about the possible ecological applications of AMNs such as filed crop protection.

The main vegetation types of Desert Grassland Nature Reserve in Qitai, Xinjiang were investigated in this paper. Based on the data from 65 plot samples, the characteristics of the main desert plant communities from the main vegetation types were quantitatively described. The results showed that, the vegetation in this reserve can be divided into 12 major plant community types: Haloxylon ammodendron Simi-Arbor and Shrub Desert Alliance, Ephedra przewalskii Simi-Arbor and Shrub Desert Alliance, Gymnocarpos przewalskii Simi-Arbor and Shrub Desert Alliance, Reaumuria soongarica Simi-Arbor and Shrub Desert Alliance, Iljinia regelii Semi-Shrub and Herb Desert Alliance, Anabasis brevifolia Semi-Shrub and Herb Desert Alliance, Tamarix laxa Deciduous Broadleaf Shrubland Alliance, Kalidium foliatum Semi-Shrub and Herb Desert Alliance, Ajania fruticulosa Semi-Shrub and Herb Desert Alliance, Achnatherum splendens Tussock Grassland Alliance, Leymus angustus Tussock Grassland Alliance, Phragmites australis Tussock Grassland Alliance. Finally, 15 associations were derived from these 12 major community types.

Pollen record is an essential data for reconstructing paleovegetation and paleoclimate. It is important for the studies of paleoenvironmental evolution, characteristics of paleoclimate change and simulation of paleobiogeochemical cycles from site to regional and global scales. In this paper, we collected and sorted out the pollen data records from published and unpublished Chinese literature between 1960 to 2020. The records included sample numbers, sampling locations (latitude, longitude and altitude of sampling sites), sample types, data sources, data types, surrounding vegetation, references, and pollen taxa, their compositions as well. They were filtered and standardized to integrate a pollen dataset of China. This dataset consists of 4 497 modern pollen sampling sites, including 660 published data from the Chinese Quaternary Pollen Database, 1 763 from early published data and 2 074 from recently collected data, belonging to 772 pollen taxa. The samples were mainly from surface soils (3 332 sites), and the rest were from moss plosters, surface sediments from lakes and the ocean. The sampling sites are widely scattered around China representing different geographical regions and vegetation types: 24.91%. in the temperate desert region, 24.02% in the subtropical evergreen broad-leaved forest region, followed by the temperate grassland region (16.14%) and alpine vegetation region of Qingzang Plateau (15.83%). The data can be divided into the raw data (58%) and numerical data (42%) according to their sources, and grain count (59%) and calculated pollen percentage (41%) by data type as well. The database constructed from the samples over China during the past half-century+ period is, though by far from complete, good representation of most of the areas in China, which can be effective in the reconstruction of past vegetation and climates as modern verification.

Owing to the high carbon capture and storage capacity, salt marshes are considered an effective blue carbon sink for mitigating global warming. In addition, salt marshes are likely to increase their carbon sink capacity in the future in response to climate warming and sea level rise. Therefore, the blue carbon sink function of salt marshes has received increasing attention from the international research community. This study reviewed the five aspects comprising the key processes of blue carbon formation, photosynthetic carbon allocation, burial fluxes and sources of sedimentary organic carbon, stability of soil carbon pools and the associated microbial mechanisms, and the simulation and assessment of blue carbon sequestration potentials in salt marshes. On this basis, concerning the main knowledge gaps, this paper proposes further research on the effect of vegetation distribution pattern along the land-to-sea hydrologic gradient on photosynthetic carbon fixation and allocation, the response of soil organic carbon deposition and burial to global change, the stability of soil carbon pools and its lateral exchange, blue carbon simulation and assessment of blue carbon sink potential in the context of climate change and sea level rise, and technologies and approaches of blue carbon sequestration in salt marshes. Prioritizing these research topics may elucidate the formation processes and mechanisms of blue carbon, predict the changing trend of blue carbon sequestration potential under global changes, and offer new insights into achieving the goal of “carbon peak and carbon neutrality”.

Recent advances in solar-induced chlorophyll fluorescence (SIF), which is a complement to optical remote sensing based on greenness observation, have made it possible to monitor the photosynthesis of plants in terrestrial ecosystems using state-of-the-art technologies. With the rapid development of tower-based, unmanned aerial vehicle (UAV), airborne and space-borne SIF observation technology and improving understanding of SIF mechanism, SIF is providing essential data support and mechanism understanding for the estimation of biological traits and gross primary production of terrestrial ecosystem, early detection of abiotic stress, extraction of photosynthetic phenology and monitoring of transpiration. In this review, we first introduce the fundamental theory, the observation systems and technologies and the retrieval method of SIF. Then, we review the applications of SIF in terrestrial ecosystem monitoring. Finally, we propose a roadmap of activities to facilitate future directions and discuss critical emerging applications of SIF in terrestrial ecosystem monitoring that can benefit from cross-disciplinary expertise.

Stable hydrogen and oxygen isotope analysis provides an important tool for calculating plant root water uptake amount, determining the contribution to plant water source, and evaluating plant water use strategy, and is thus of great relevance to ecohydrological studies with respect to exploration of the water transmission mechanism of the atmosphere-vegetation-soil system. However, the stable hydrogen and oxygen isotope ratios (δ²H and δ¹⁸O) offset between soil and xylem water can cause inconsistency in the calculated contribution rate of plant water source, but the reasons for differences in hydrogen and oxygen isotope results are unclear. In this review, we first briefly introduced the phenomenon of hydrogen-oxygen stable isotope ratio offset; secondly, the framework was constructed along the water transport path of the soil-plant-atmosphere continuum. We systematically expounded the natural effects of δ²H and δ¹⁸O offset in three interfaces (plant-atmosphere interface, soil-atmosphere interface, and root-soil interface) and two spaces (plant and soil layer). At the same time, we summarized the methodological artifacts that are associated with soil and xylem sample extraction and δ²H and δ¹⁸O determination technologies. Finally, we identify main knowledge uncertainties according to the existing research progress; and highlight three areas that deserve future research attention: the acquisition of isotope spatiotemporal data, the cause of micro-scale isotope offset, and the optimization of extraction and determination technology.

Understanding the response patterns and potential mechanisms of structure and function in grassland ecosystems to nitrogen (N) enrichment is essential to evaluate ecological impacts of external N input. The muti-level N manipulative experiment offers the possibility to explore the nonlinear response patterns and associated mechanisms of structure and function in grassland ecosystems to additional N input. In this review, we summarized the impacts of additional N inputs on community diversity, carbon (C) and N cycling in grassland ecosystems around the world. Numerous studies illustrated that N enrichment induced the decline of plant species diversity, plant functional diversity and soil bacteria richness in grassland ecosystems, yet the change of fungal diversity was not significant. Above- and below-ground plant productivity showed different responses to N input: aboveground plant productivity exhibited initial increasing and subsequent saturation trends, but root productivity and root:shoot ratio showed downward patterns, and root turnover rate appeared a single-peak pattern of first increasing and then decreasing with the continuous increase of N addition rate. Meanwhile, different C decomposition processes responded variously to N enrichment. Specifically, litter decomposition rates exhibited multiple response of “exponential decrease, liner increase or insignificant change with N addition level”. However, the relationship of soil respiration and CH₄ consumption with N addition was dominated by a single peak trend of increasing at low to medium N levels but declining at high N levels. Likewise, different soil C fractions showed multiple response patterns to N input. N addition generally stimulated soil C storage and particulate organic C accumulation, while the mineral-associated organic C exhibited divergent responses of “increase, unaltered, and decrease” along the N addition gradient. In addition, plant N uptake exhibited initial increasing and subsequent situation trends along N addition gradients, while different soil N transformation processes showed differentiated responses along N addition gradients and the relationship between N₂O emission and N addition rate varied among various grassland ecosystems. An exponential increase of N₂O fluxes with N addition rate was observed in temperate grasslands, while the patterns of first increase and then saturation or linear increase of the N-induced changes in N₂O emissions had been discovered in alpine grasslands. Future studies should focus on the nonlinear responses of rhizosphere processes and phosphorus (P) cycle to external N input, and also explore potential mechanisms from the aspect of multi-dimensional biodiversity changes.

China has the largest area of tree plantations in the world, and how to maintain the long-term stability of plantations has become one of the major challenges in the context of climate change. Pinus sylvestris var. mongolica is one of the most important coniferous evergreen tree species in the well-known “Three-North” Shelterbelt Construction Program in China, due to its properties of tolerance to drought, low temperature, and open land condition. Afforestation with P. sylvestris var. mongolica in northern China provides great benefits to environmental protection and ecosystem carbon fixation. However, with the growth of the stands and the ongoing climate change, P. sylvestris var. mongolica plantations in a fragile habitat of sandy land have been subjected to increasingly severe water stresses. Typically, the phenomenon of premature dieback has occurred in some of the P. sylvestris var. mongolica plantations, such as at the sites of Zhanggutai in the southern edge of Horqin Sandy Land, which causes great concerns on the stability of the local ecosystems. Based on recollections of studies on the basic biological characteristics and introduction history of P. sylvestris var. mongolica, we summarized the recent research achievements in understanding the forest-water relationships in P. sylvestris var. mongolica plantations, and examined the main contradictions in the forest-water relationships in P. sylvestris var. mongolica plantations under the climate change scenario. We recommend adjustment of several stand management measures based on the compromised forest-water relationships: (1) turning the single goal for environmental protection into multi-objectives with balanced consideration for stand structural stability, carbon sequestration, and sustainable development; (2) adopting more measures for improving soil conditions rather than for developing forest landscapes; and (3) establishing the sustainable shelterbelts by combining afforestation with natural regeneration rather than by merely depending on natural regeneration processes. Based on the condition of fragile sandy land and climate change, we should still regard P. sylvestris var. mongolica as a pioneer and construction tree species. In consideration of the principle of “determining forest cover by water supply”, the uneven-aged forest stands can be established by conducting alternate-row harvesting followed by replanting. As a result, the environmental protection function and carbon sequestration capacity can be continuously improved, the ecological services and productivity can be maximized, and the biodiversity and stability of the ecosystem can be protected and guaranteed. The findings from this study can be of important values for guiding the systematic management of northern ecological shelterbelts.

Aims Soil nitrogen (N) plays a vital role in regulating the structure and function of ecosystems and is affected by N deposition. Most previous studies focus on the responses of the N content in bulk soil to N deposition, but the responses of the N content in different soil organic matter (SOM) fractions remain unclear. We aimed to investigate how long-term N addition influenced soil N of different SOM fractions in a semi-arid grassland.

Methods A manipulated N addition experiment with 4 levels of N addition (0, 8, 32 and 64 g·m^-2·a^-1) has been conducted for 13 years in Duolun country, Nei Mongol. SOM was separated to particulate organic matter (POM) and mineral associated organic matter (MAOM) by density fractionation. The plant and soil properties were also measured.

Important findings The results showed that N addition had no significant effect on the carbon (C) content in bulk soil, POM, or MAOM. With increasing levels of N addition, the N content in bulk soil and in POM increased significantly. Furthermore, we found that the increased N content of POM was mainly associated with greater aboveground biomass following N addition. The N content of MAOM is mainly correlated with soil texture, but was not affected by N addition. These results suggest that continuous N addition can increase the soil N in bulk soil, but the increased N is mostly distributed in labile POM pools, which can be vulnerable to land use and climate change.

Aims Altitude has prominent effects on many environmental factors, such as atmospheric pressure, temperature, precipitation, soil moisture and wind velocity. The relationship between plant functional traits and altitude are critical for predicting the effects of climate change on montane plants. Our objective is to examine the effect of altitude on community-level plant functional traits in the Qinghai Lake Basin, China.
Methods Five sites were selected with 200 m increase in altitude (3 400-4 200 m) in the Qinghai Lake Basin, China. Community structure, plant functional traits, soil property and atmospheric factors were surveyed and analyzed in this study. Community-weighted mean functional traits (CWM) was calculated according to the relative abundance of species.
Important findings The results showed that: (1) Community-weighted mean plant height (H), leaf dry matter content (LDMC), leaf C:N ratio (C:N) and leaf N:P ratio (N:P) decreased significantly along altitude, while specific root surface area (SRA) fluctuated with altitude. Specific leaf area (SLA), leaf nitrogen content (LNC) and leaf phosphorus content (LPC) increased significantly along altitude, while altitude had no significant effect on leaf carbon content (LCC), root tissue density (RTD) and specific root length (SRL). (2) The variation in CWM along altitude could be explained by species turnover more rather than intraspecific variability. N:P and LPC had a positive covariation, other CWM had a negative covariation. (3) Precipitation and 0-10 cm depth soil nutrients content explained the largest proportion change of SLA. Temperature and 10-20 cm depth soil nutrients content explained the largest proportion change of other CWM along altitude. Overall, these findings suggested that the plant communities in our study adapted to altitude through species turnover, and the non-dominant species tended to occupy opposite trait spaces to the dominant species in the Qinghai Lake Basin, China. Temperature and deeper soil nutrients content had significant effects on CWM along altitude.

Phosphorus (P) is an essential but limited nutrient for plant growth, and global climate changes may affect soil P cycling and further aggravate P limitations in the soil. In this review, we focused on the response of plant P acquisition strategies to climate changes and subsequent influences on ecosystem productivity. By searching and analyzing the existing literatures, we summarized the P acquisition mechanism of plants and their response to global climate changes from following aspects: 1) plant P starvation response mechanisms; 2) plant P acquisition pathways and strategies; 3) involvements of soil microorganisms in plant P utilization; and 4) responses of plant P acquisition strategies to global climate changes (e.g., warming, nitrogen deposition and precipitation changes) and the underlying mechanisms. The review is expected to deepen our understanding of plant adaptation to low-P stress under the future climate scenario, and can also provide a theoretical basis for nutrient management in agriculture.

Interactions between plants and coexisting microorganisms have significant impacts on plant growth, development, and health. Human domestication has resulted in significant differences between modern crops and their wild ancestors in physiological and genetic characteristics and growth environment, which will inevitably affect the interaction between crops and their microbiomes. Understanding the impact of domestication on the diversity and community structure of microbiome and the mechanisms involved is an important theoretical basis for application of microbiome during crop improvement and breeding. In this review, we summarize the research progress of the effects of domestication on the community composition and diversity of root and shoot microbiome (bacteria and fungi) in crops. We also analyze the involved action pathways in shaping crop microbiomes by domestication, considering the domestication effect on crop morphology, root configuration, exudates and other physiological characteristics, and the change in growth environment. The research directions that need to be focused on in this field were proposed.

Soil organic carbon (SOC) pool is the largest carbon pool in terrestrial ecosystems and plays an important role in regulating the global carbon cycle and climate change. The inputs of nitrogen (N) and phosphorus (P) induced by anthropogenic activities and atmospheric deposition of N and P increase the availabilities of N and P in terrestrial ecosystems, which in turn will have important impacts on SOC dynamics via regulating plant growth and microbial activity. At present, many field-manipulation experiments regarding the effects of N addition and/or P addition on the dynamics of SOC have been conducted worldwide, and some breakthroughs and progress have been made, but a systematic and comprehensive review and summary of them is still lacking. By taking the effects of N addition and/or P addition on the inputs and outputs of soil carbon as the starting point, we systematically reviewed the effects of N addition and/or P addition on SOC and the potential mechanisms from three aspects: the size, fraction and molecular composition of SOC. According to the results of previous studies, N addition, P addition, and combined N and P (N + P) addition generally stimulate the size of SOC pool. The stimulation effect of N is caused by the decreased carbon outputs from microbial decomposition and/or the enhanced carbon inputs of plant above- and/or below-ground under N addition. However, the stimulation effect of P may be dominated by the enhanced carbon inputs of plant above- and/or below-ground under P addition. As for the fractions of SOC separated by particle-size or density fractionation, N addition promotes both labile fractions (particulate organic carbon or light fraction carbon) and stable fractions (mineral-associated organic carbon or heavy fraction carbon) of SOC, but reduces the proportion of stable carbon fractions to total SOC. In addition, the effects of N addition on the molecular composition of SOC are complex and diverse, and are regulated by environmental and experimental factors such as soil N availability, N addition rate, and N fertilizer form. Compared with N addition, studies on the effects of P addition and N + P addition on the fraction and molecular composition of SOC are very limited, and the associated mechanisms for the effects of P addition and N + P addition on these variables are still unclear. To improve our understanding, we propose four aspects of studies that need to be strengthened in the future, including the effects of P addition on SOC in different types of ecosystems (especially tropical forests), the role and relative contribution of plants and microorganisms in regulating the changes of SOC and its fractions under N addition and/or P addition, the effects of long-term N addition and/or P addition and their interactions on SOC, and the effects of N addition and/or P addition on SOC in deep soils (below 20 cm).

Aims As one of the major terrestrial ecosystems of the world, a small fluctuation of grassland soil carbon (C) would affect the carbon cycle of the terrestrial ecosystem and ecosystem multifunctionlity (EMF). The carbon accumulation rate (CAR) of aboveground community well reflects the capacity and efficiency of carbon sequestration in a field from the start to the peak of a growing season. The changes in plant CAR could influence the ability of above- and below-ground community. Currently, the majority of studies have primarily focused on the relationship between community diversity and EMF, while the linkages of CAR with EMF were understudied. We aimed to explore the process and underlying mechanism of how CAR affecting EMF in alpine grassland community. Our results would improve the understanding of EMF maintenance mechanism and provide theoretical support for alpine ecosystem management.
Methods We conducted a field transect survey which consists of a total of 115 sample sites of alpine grasslands on the Qingzang Plateau from July to August 2015. The ecosystem multifunctionality index (M) was calculated from 13 key ecosystem parameters including soil organic carbon content, total nitrogen content, total phosphorus content above- and belowground biomass etc. The normalized difference vegetation index (NDVI, 1982-2013) was adopted to obtain the phenology in 2015. We calculated the CAR value. To explore the underlying mechanism of how CAR affecting EMF, the annual total precipitation and temperature were extracted by the method of thin disk smooth spline interpolation based on observations of meteorological stations from 2011-2015.
Important findings Belowground biomass, soil organic carbon content, total phosphorus content and microbial biomass carbon content had high weighting for CAR (0.58, 0.80, 0.83 and 0.79) and M (1.05, 0.98, 1.02 and 0.97). There was a significantly positive correlation between CAR and M (R² = 0.45, p < 0.01). Our findings suggested that the synergism of plant community and soil elements affected CAR and further regulated EMF under the influences of precipitation and temperature.

Aims Condensate is an important water source for plants in the ecosystems of drylands. Previous studies have found that some desert plants can absorb condensate via leaves. This study aimed to determine the capacity of the foliar condensate absorption of typical shrub species (Artemisia ordosica and Salix psammophila) in the Mu Us Desert, and to explore the pathways of foliar condensate absorption and transport.

Methods The dehydrated and non-dehydrated detached shoots of A. ordosica and S. psammophilawere placed in an artificial chamber and exposed to deuterium labelled condensate, and the foliar condensate absorption was determined by comparing the differences of shoot masses and isotopic signals between pre- and post-immersion. The potted whole plants of A. ordosica and S. psammophilawere placed in an artificial chamber and exposed to fluorescent tracer solution, and the pathways of foliar water uptake and transport were determined by comparing the differences of fluorescent tracing in leaves and twigs between pre- and post-immersion.

Important findings (1) After the deuterium labelled dew exposure, no significant differences were found in shoot masses between pre- and post-immersion of non-dehydrated detached shoots of A. ordosica and S. psammophila. However, the dehydrated shoot masses significantly increased by 2.04% and 6.74% in A. ordosica and S. psammophila, respectively; the δD (stable isotope ratio of hydrogen) of leaf water increased by 170.10‰ and 104.09‰ in A. ordosica and S. psammophila, respectively; and the δD of xylem water increased by 10.52‰ and 12.72‰ in A. ordosica and S. psammophila, respectively. (2) After the fluorescent tracer solution exposure, fluorescence was observed in the cuticles, stomata, spongy mesophyll, palisade cells and vascular bundle of the leaves of A. ordosica and S. psammophila. The fluorescence was also found in collenchyma of the leaves of A. ordosica. In addition, the fluorescence was observed in phloem, xylem, and pith of twigs of two shrub species. This study found that two typical shrub species in the Mu Us Desert had the capacity to absorb condensate via their leaves, and the plants undergoing water stress had the higher capacity of foliar condensate absorption. The leaves of A. ordosica and S. psammophilaabsorbed condensate through cuticles or stomata, and the absorbed water was transported to vascular bundle and even twigs. Foliar condensate absorption may be an important water use strategy to survive for A. ordosica and S. psammophila during dry periods.

Alpine shrublands, as a zonal vegetation, are widely distributed on the Qingzang Plateau, and play ecological functions such as soil and water conservation, conservation of water resources, and biodiversity protection in the regional ecosystem. This study used a unified and standardized method to set up 58 quadrats to investigate the species composition, quantitative characteristics and habitat information of the main alpine shrublands of the Haizi Mountain in Batang, China. Based on “Vegegraphy of China” compilation and research standards, the alpine shrublands in this area can be divided into three vegetation types, 11 alliances, and 21 associations. This paper presents descriptions on the characteristics for each association and provides the original data from all survey plots.

Aims Hydraulic failure is one of the primary cause of plant mortality during drought. Thus, quantitative analysis on inter-specific and inter-organ variance in hydraulic traits can help us to predict the response and even survivability of species under climate change.

Methods Here, three Podocarpaceae species (Podocarpus macrophyllus, P. macrophyllusvar. maki and Nageia nagi) grown in a mesic common garden were studied, with xylem hydraulic function (specific hydraulic conductivity (K_s); embolism resistance (P₅₀)), anatomical structure (tracheid diameter (D_t); hydraulic diameter (D_h); tracheid wall thickness (T_w); tracheid density (N_t); pit membrane diameter (D_p); pit density (N_p)) and mechanical strength (wood density (WD); tracheid thickness to span ratio ((t/b)²)) measured. Then, we analyzed hydraulic traits variance at the organ level (stem and root) in three Podocarpaceae species, and investigated the relationships among xylem hydraulic traits, anatomical structure and mechanical strength in stems and roots.

Important findings We found that: 1) The stem xylem in three Podocarpaceae species exhibited no safety- efficiency trade-off. In contrast, the root xylem exhibited safety-efficiency trade-off. 2) For stems, K_s was positively correlated with D_p, but decoupled with stem WD and (t/b)²; Stem P₅₀ was negatively correlated with D_p, but not correlated with WD and (t/b)². 3) For roots, K_s was positively correlated with hydraulic diameter, but negatively correlated with root T_w and (t/b)²; Root P₅₀ was positively correlated with T_w, (t/b)² and WD. Root xylem traits exhibited strong relationships with both K_s and P₅₀, demonstrating its cause-and-effect basis for the safety-efficiency tradeoff. On the other hand, the absence of safety-efficiency tradeoff in stems may be attributed to the overbuilt xylem of Podocarpaceae. More experimental evidence on the overbuilding of xylem is desired in the future study.

Aims Impatiens davidii, a rare ornamental flower endemic to China, had a small wild population and depended on pollination of Bombus trifasciatus. As I. davidii has a specialized pollination system, pollination resources were one of the important factors limiting its population diffusion.

Methods In this study, the maximum entropy (MaxEnt) model was used to simulate the potential distribution area of the two species based on 63 distribution records of I. davidii, 54 distribution records of B. trifasciatus, and 19 climatic factors. The potential distribution of the two species under three climate representative concentration pathway scenarios RCP2.6, RCP4.5, and RCP8.5 were predicted for the future (2050s, 2070s).

Important findings The results showed that the main environmental factor affecting the distribution of I. davidii was precipitation of warmest quarter. Under the current climate conditions, the range overlap, niche overlap, and niche breadth of two species were higher. Approximately 99.09% of the suitable areas of I. davidiiwas overlapped with B. trifasciatus, which ensured the pollination resources to a large extent. Under the three future climate scenarios, the distribution area of I. davidii will expand to northeast and north China, and the suitable habitat area will increase by 66 000-221 900 km². The suitable habitat area of B. trifasciatus moved northward slightly, and increased by 44 800-155 000 km². The proportion of suitable habitat areas of I. davidii overlapped with B. trifasciatus decreased by 1.40%-9.00%, indicating that the suitable area of I. davidii might be affected by climate change and lack of pollination resources in the future.

Aims When the external environment changes, plants can change their own functional traits and adjust adaptation strategies in a timely manner. Therefore, plant functional traits can effectively reflect the response of plants to the change of grassland use. However, there are few studies on the effects of grassland use patterns from the perspective of plant functional traits in the Nei Mongol grassland. Therefore, from the perspective of functional traits, this paper reveals the adaptation strategies of plants after external disturbances, aiming to provide basic data support and scientific basis for the sustainable management of natural grasslands.
Methods In this study, four important dominant species of Stipa grandis, Leymus chinensis, Cleistogenes squarrosa and Artemisia frigida in the typical grasslands of Nei Mongol were selected as the research objects to explore the differences in the functional traits of dominant species under the influence of long-term free grazing, mowing, short-term enclosed and long-term reservation.
Important findings We found that: 1) Vegetation height, root length and carbon and nitrogen concentration of dominant plants in Nei Mongol typical grasslands are reduced under long-term grazing. Changes in these traits can miniaturize individual plants and reduce their palatability, indicating that plants may adopt avoiding grazing strategy to adjust to the interference of long-term free grazing. Under the mowing management, the vegetation height and specific leaf area of the dominant species tend to increase. Among them, the nitrogen content of A. frigida is the most sensitive to the response of mowing. The nitrogen concentration in its roots, stems, leaves are the lowest in the mowing sites; the carbon and nitrogen concentration of plants increases under enclosure and long-term non-disturbance treatments, indicating that the plant transforms from resource acquisition strategy to resource storage strategy through changes in functional traits when the disturbance intensity is reduced. 2) The analysis of the assemblage of functional traits of dominant species shows that C. squarrosa has a small plant height and a high specific leaf area, and A. frigida has a high lignin and nitrogen concentration. The two species thus can adopt some avoidance (escaping from grazers) and tolerance (regrowth capacity after defoliation) strategies to improve their grazing resistance; S. grandis has the highest plant height, the largest leaf dry matter concentration, the highest stem and leaf cellulose concentration, which indicates that S. grandis is a very typical competitive species. Under management conditions with low interference intensity, the competitive pressure of S. grandis (Competitive strategy) against other species may be an important reason for its high dominance.

Aims Accurate assessment of plant aboveground biomass is important for optimizing grassland resource management and for understanding the balance of carbon, water and energy fluxes in grassland ecosystems. This study constructed the optimal empirical models by near-surface remote sensing normalized difference vegetation index (NDVI) data, and then estimated plant aboveground biomass in an alpine grassland on the Qingzang Plateau.
Methods Using the dataset of both the field-measured aboveground biomass and the NDVI_RS observed by plant canopy spectrometer (RapidSCAN), we constructed the empirical models for estimating aboveground biomass in different phases of the growing season across 2018 and 2019. Using the NDVI_Cam time series observed by phenology camera and the estimated models, we simulated seasonal dynamics of aboveground biomass in 2018.
Important findings (1) The seasonal dynamics of NDVI_Cam, NDVI_RS and aboveground biomass exhibited a similar unimodal pattern; however, the timing of peak NDVI (August) preceded that of peak aboveground biomass (July). (2) The best model for estimating aboveground biomass is the power function in May, July and September, and the quadratic equation in June and August. The estimation accuracy ranged from 0.29 to 0.77. (3) The estimation of aboveground biomass based on the models in different phases of growing season (R² = 0.91) showed a higher accuracy compared to that based on the model at a single time (September)(R² = 0.49). Our results suggest that the near-surface remote sensing is an effective approach for estimating alpine grassland aboveground biomass, and further investigation on the seasonal growth of plants will help accurately evaluate grassland resources.

Changes in soil nutrient availability and primary succession of vegetation often co-occur during the processes of natural soil development. A low availability of nitrogen (N) and phosphorus (P) resources is common in the very early and late stage of soil development, respectively. Plants have evolved different nutrient-acquisition strategies (NASs) in response to low nutrient availability. Although the changes and responses of plant NASs to soil nutrients may affect primary succession and species diversity, the temporal trends and underlying mechanisms of plant NASs with soil development remain unknown. We reviewed 104 studies mainly carried out on soil chronosequences to clarify changes in plant NASs with soil age and its ecological significance. We classify plant NASs into Fine root, Microbial, Specialized root, Carnivorous and Parasitic strategies. We argue that the diversity of plant NASs changes with increasing soil age following a dumbbell-pattern, while reaching the maximum in the late stage of soil development. The role of Microbial and Fine root strategies in plants acquiring nutrients gradually decreases with increasing soil age, while the minimum and maximum role of Specialized root strategies in plants acquiring P is in the intermediate and late stages of soil development, respectively. The effects of NASs on interspecific relationships of plants vary with soil age. Specifically, pioneer plants with biological N fixation and specialized root strategies usually increase available soil N and regolith-derived nutrients to facilitate the colonization of subsequent plants in the early stage of soil development. During the early-intermediate stage, NASs mainly affect plant competitiveness in acquiring relatively abundantly available nutrients from soil. The facilitation and competition affected by NASs contribute to plant species turnover in the first two stages. In the late stage, diverse NASs enable plants to acquire distinct forms of nutrients from different soil spaces and complementary NASs enable plants to take up soil nutrients mobilized by their neighbors. Together with the interactions between NASs and soil pathogens, these processes contribute the coexistence and diversity of plant species in this stage when most soil nutrients have a very low availability. We propose that it is necessary to quantify the relationships between changes in soil nutrient availability (including concentrations and fractions) and plant NASs with soil age. More studies are also needed to quantify contributions of NASs to primary succession, diversity of plant species and soil development.

Aims As a key factor of nutrient cycling in ecosystems, soil enzyme activity is an important indicator of soil quality and ecosystem function. However, there have been very few studies on the differences of soil enzyme activities among different types of alpine grassland ecosystems. Thus, the aims of this study were to compare the differences of soil enzyme activities among five different types of alpine grassland and to reveal their influencing environmental factors on the Qingzang Plateau.
Methods Totally, 21 samples of five alpine grassland types, including alpine meadow, alpine steppe, alpine meadow steppe, alpine desert steppe and alpine desert on northern Qingzang Plateau, were selected for field in-situ investigation and sampling. The activities of 14 enzymes involved in the cycling of carbon (C), nitrogen (N) and phosphorus (P) were determined, and the relationships between enzymatic activities and environmental factors in alpine grassland were established.
Important findings The activities of C-acquisition (invertase, cellulase, β-1,4-glucosidse, polyphenol oxidase and peroxidase), P-acquisition (alkaline phosphatase) enzymes and two N-acquisition (arylamidase and nitrite reductase) were significantly different among different alpine grassland types. Moreover, correlations were found among C-acquisition, N-acquisition and P-acquisition enzymes. A significant positive correlation was found between invertase and alkaline phosphatase, and between cellulase and N-acetyl-α-D-glucosaminidase. A significant negative correlation was found between polyphenol oxidase and nitrite reductase, N-acetyl-β-D- glucosaminidase. Soil organic matter (SOM) content, gram-negative bacteria content, ratio of nitrogen to phosphorus, gram-positive bacteria content, bacteria content, actinomycetes content, total nitrogen content and fungi content were the key factors influencing soil enzyme activity among the 19 environmental indicators, and SOM content had the greatest impact (explained 11.9%). The results demonstrated that the activities of C-acquisition, P-acquisition and two N-acquisition (arylamidase and nitrite reductase) enzymes were significantly different among different types of alpine grassland, and soil enzyme activities were mainly controlled by SOM content, microbes and N elements in alpine grassland ecosystems.

Aims Soil enzymes play an important role in the process of soil nutrient transformation. The main purpose of this study is to explore the chemical composition of soil organic matter and its effect on soil protease and urease activity in alpine grasslands in Northern Xizang, China.
Methods The pyrolysis Gas Chromatograph/Mass Spectrometer (Py-GC/MS) was used to obtain the chemical compositions of soil organic matter, and to analyze the relationships between soil chemical compositions and soil enzyme activity in five alpine grasslands, including alpine meadow, alpine steppe, alpine meadow steppe, alpine desert steppe and alpine desert ecosystems.
Important findings The results showed that the enzyme activities among five alpine grassland soils (0-15 cm) were different. Soil urease activity was significantly higher than soil protease activity in the alpine desert steppe, while the difference between the urease and protease activities was not significant in other types of alpine grasslands. Soil protease activity was significantly different among five alpine grassland types, but soil urease activity was not. The correlation analysis showed that soil protease activity was closely related to the relative abundance of alkanes, alkenes and aromatics in soil organic matter and the ratio of furfural to pyrrole. However, the correlation relationships between urease activity and soil organic matter chemical compositions were not significant. The results indicated that alpine grassland type and soil organic matter chemistry were the key factors affecting soil protease activity, but their effects on soil urease activity was non-significant, which calls for further study on the influencing factors on soil urease activity.