Trade-offs among plant functional traits reflect the trade-off relationships between resource acquisition and conservation of different plants, which are of pivotal importance for understanding the mechanisms by which plants adapt to the environment. However, due to the heterogeneity of the soil environment and the limitations of technical means, the study of below-ground root functional traits and their interrelationships is currently lagging behind that of above-ground functional traits. Traditionally, fine roots have been defined as all roots ≤2 mm in diameter. The acquisition and utilization of soil resources by plants depends on architectural traits, morphological traits, chemical traits and biotic traits of fine roots and so on, including fine roots associations with mycorrhizal fungi. Recently, the root economics space has been proposed, which demonstrates the existence of trade-offs between the do-it-yourself strategy of plants increasing their own root surface area and the outsourcing strategy of investments into fungal symbionts for enhanced nutrient mobilization from hyphal expansion, in addition to the traditional trade-offs between fast (high nitrogen content and metabolic rate) and slow (high tissue density) investment return. It was found that thin-root species obtained soil resources mainly by increasing specific root length, whereas thick-root species relied more on mycorrhizal fungi. However, the carbon economy of resource acquisition through the root and mycorrhizal hyphal pathways remains unclear. In future research, the key issues of root functional traits were suggested as follows: 1) for research methods, it is urgent to establish a unified set of definitions and research methods for root classification, sampling, storage, functional traits and their research methods; 2) for research traits, the research of “hard” traits of fine roots should be strengthened; 3) for the trade-offs between functional traits of fine roots, it is of great significance to strengthen the study of the trade-offs between construction costs and resource benefits between plant roots and mycorrhizal fungi.

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.

Plant functional traits are generally defined as relatively stable and measurable morphological, physiological, and phenological characteristics of plants that can indirectly affect plant growth, reproduction, and survival. Years of development have enabled the standardization of the definition, connotation, and measurement methods of plant functional traits. Now, the intraspecific and interspecific variation, biogeographic patterns, coordination, and the evolution of plant functional traits have been well explored. The gradual development of global plant functional trait databases since the 1990s has led to the expansion of plant functional traits beyond individual and local scales. Regional and global biogeographical studies on plant functional traits are gradually exploring community species coexistence mechanisms and maintenance of ecosystem functions. Researchers have found that traditional plant trait databases, which were created from published studies, have insufficient data to provide answers to questions about natural ecosystems. Therefore, constructing a plant trait database that considers compatibility and orderliness is crucial. As new databases and scientific concepts have emerged, the following areas have become the focus of studies on plant functional traits: 1) coordination between functional traits of different plant organs, and holistic examination of plant response to environmental changes; 2) multi-dimensional response and adaptation of various plant functional traits, and proposal of the concept of a plant trait network; 3) consideration of the complexity of plant community structure, and exploration of community assembly using plant functional diversity and trait moments; and 4) refinement of the scaling method for different levels of ecological organization, and recognition of plant community and ecosystem traits as critical bridges between plant traits and macroecology. These directions have pushed for the application of traditional functional trait research to natural, social, and economic systems, thus promoting the rapid development of trait-based studies to further solve regional eco-environmental problems.

Arbuscular mycorrhiza (AM) is one of the oldest symbionts between plants and soil microorganisms, and about 80% terrestrial plant species can associate with AM fungi on earth. Because of the stable climate and poor soil phosphorus content in tropical and subtropical forests, this mutualistic symbiosis is much more common there. Previous studies have extensively investigated the diversity of AM fungi in tropical and subtropical forests, and have shown that AM fungi can promote plant recruitment and growth. However, this positive effect of AM fungi on plants (i.e., the positive plant-soil feedback) can weaken the contribution of the negative plant-soil feedback (caused by soil-borne pathogens) to maintaining tree species diversity, which appears to contradict with the surprisingly high tree diversity and high proportion of rare tree species in tropical and subtropical forests. Recently, a mounting number of empirical studies have found that the diversity of AM fungi varies significantly in different habitats and AM colonization depends on the identity of host species, thereby affecting the fitness of plants and further shaping the plant community structure. Through synthesizing the current research about the diversity of AM fungi in promoting plant coexistence and maintaining community diversity, we expect to put forward a promising study direction for testing the “rare species advantage” hypothesis, therefore improving the conservation of rare plant species.

Aims Haloxylon ammodendron is the major dominated species in the Gurbantünggüt Desert, which plays a key role in ecosystem services: such as biodiversity conservation and prevention of dryland degradation. Frequent droughts have a significant impact on the survival of H. ammodendron, thus understanding the drought resistant strategies of H. ammodendron is essential for the sustainability and stability of desert ecosystems. Robust hydraulic system and carbon balance are important parts of the drought resistance mechanism, but the hydraulic threshold for survival of H. ammodendron under drought stress are still unquantified.

Methods We set up a control group and a drought treatment group for adult H. ammodendron, and determined the water status of assimilation twigs, the loss rate of xylem hydraulic conductivity in branches, gas exchange characteristics, nonstructural carbohydrate (NSC) contents and morphological characteristics at upper, lower and middle branches of H. ammodendron. We used one-way ANOVA for each trait among different treatments and heights, linear regression for stomatal sensitivity and principal component analysis for drought resistance of H. ammodendron, respectively.

Important findings (1) The predawn and midday water potential of assimilation twig, assimilation twig water content and branch water content of H. ammodendron decreased under drought stress, but did not affected by the increase of height; P50 and P88 (xylem tension causing 50% and 88% loss of maximum hydraulic conductivity) did not change significantly under drought and with increasing height, and the mean value of P50 was -4.12 MPa and P88 was -7.10 MPa for each height and treatment groups, while the hydraulic safety margin was significantly reduced under drought. (2) The stomatal opening of H. ammodendron was not sensitive to drought stress, and thus drought stress and branch height increase did not significantly affect net photosynthetic rate and stomatal conductance in general. (3) The NSC contents of assimilation twigs and branches did not decrease under drought stress or with increasing branch height; the value of NSC contents in the assimilation twigs and branches were 22.11% and 13.10% higher, compared to the control group. (4) The Huber value of H. ammodendron increased by 73.78% in the drought treatment group compared to the control group; the specific leaf area decreased by 14.60% compared to the control group, but there were no significant difference between the two treatment groups. In conclusion, the hydraulic traits of H. ammodendron were significantly affected by drought stress, but not by the increase of branch height, and there was no hydraulic limitation with increasing branch height. Under drought stress, the risk of simultaneous hydraulic failure of the peripheral branches at the crown edge was high, the hydraulic safety margin (difference between midday assimilation twig water potential and P88) was only 40.85% of that of the control group. Due to the low sensitivity of stomata to water stress, the shrub can maintain the capacity of photosynthetic carbon fixation under drought stress, and even slightly increased NSC contents of the assimilation twigs and branches.

Litter often decomposes more rapidly in its native habitat (“home”) than in non-native habitats (“away”), a phenomenon called the “home-field advantage”. To explore the driving mechanism of home-field advantage of litter decomposition is important to predict the process of plant nutrient return and ecosystem carbon budget. This study reviewed the research progress on the home-field advantage of litter decomposition in recent years by discussing the quantification of home-field advantage, the controlling factors, and related driving mechanisms. There are four common metrics to describe home-field advantage in litter decomposition, and the use of linear model analysis to calculate home-field advantage is more appropriate. Litter quality (chemical composition, etc.) and soil microbial community structure are the main factors influencing the home-field advantage of litter decomposition, and soil fauna, climatic conditions, decomposition time, plant life form and growth form can also influence the intensity of the home-field advantage. Greater differences in litter quality usually generate stronger home-field advantage. Microbial taxa in the soil drive the home-field advantage of litter decomposition, but the role of soil microbes is often mediated by animal and climatic disturbances. In addition, the existence of phyllosphere microbes makes the home-field advantage of litter decomposition stronger. The litter chemical convergence hypothesis, decomposer control hypothesis and substrate quality-matrix quality interaction hypothesis are major hypotheses explaining the home-field advantage in litter decomposition, but they are not impeccable. We believe that the association between litter and soil microbial community is the driving force behind home-field advantage. The current researches on the factors and relative contribution of home-field advantage are not deep enough and usually focusing on a single ecosystem. Future investigations should explore deeper on the factors and their relative contributions of home-field advantage, and focus on more ecosystem types to improve the understandings of the mechanism of home-field advantage.

Aims Grazing, one of the primary ways of grassland utilization in Nei Mongol, has essential influences on plant community properties of grasslands. However, the comprehensive response patterns of Nei Mongol grassland plant community properties to grazing remain unclear.
Methods Based on a dataset derived from 76 studies, the plant community characteristics and soil physicochemical properties of Nei Mongol grasslands under different grazing intensities, different grassland types and different grazing years were integrated and analyzed in order to comprehensively evaluate the response patterns of Nei Mongol grasslands to grazing.
Important findings Our results showed that grazing significantly reduced plant above/below ground biomass, cover, height, density, species richness, Shannon-Wiener diversity index, Pielou evenness index, Simpson diversity index, and soil water content. The negative effects of grazing were strengthened with increasing of grazing intensity and duration. Moreover, grazing had a greater negative effect on the grasslands with sparse vegetation and low environmental carrying capacity (e.g., desert grasslands, sandy areas, etc.). This study shows that the responses of plant community characteristics to grazing in Nei Mongol grasslands are regulated by multiple factors, and appropriate grazing intensity and grazing time should be set according to different types of grasslands to achieve sustainable utilization of grasslands. The standards of grazing intensity in current grazing studies are not uniform, making it difficult to compare different studies, and the results from some studies do not have statistical significance due to a lack of replications in the experiment. The exploration of uniform quantitative standards for grazing intensity will be an important and challenging issue in future grazing studies, and the rationality of experimental design should also be emphasized.

Aims The southwestern China is a region with complex topography and diverse ecosystem and vegetation types. However, its role as an ecological barrier is being weakened by the effects of climate change and increasing pressure of human activities. This study examines the temporal dynamics of vegetation carbon use efficiency (CUE) in this region using the CMIP6 models, aiming to effectively reducing the uncertainties in prognostic results of future predictions.
Methods We used MODIS remote sensing data for the period 2001-2014 and simulations from 15 models in the Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to determine the capability of the new generation models in simulating the seasonal and annual vegetation CUE in the southwestern China. The performance of the models was ranked based on the composite rating index (MR).
Important findings Most of the models used in this study underestimated the annual vegetation CUE, and their ability to simulate the spatial patterns in the trends of vegetation CUE is generally poor. However, some models performed relatively well in simulating the spatial distribution of multi-year average vegetation CUE; the top 1/3 tier included BCC-CSM2-MR, CMCC-ESM2, TaiESM, EC-Earth3-Veg and CAS-ESM2-0 in the order of performance. Among the seasons, the models best simulated the spatial distribution of vegetation CUE in summer, with better results from BCC-CSM2-MR, EC-Earth3-Veg, TaiESM, CMCC-ESM2 and CAS-ESM2-0. The simulation capability of the models for winter is second only to that for summer, and relatively poor for spring and autumn. Compared to the simulations by individual models, the multi-model ensemble mean (MME-S) reduced the uncertainties and exhibited a strong simulation capability, especially in the spatial distribution of vegetation CUE in local areas such as the Sichuan Basin. There was a lack of good simulation capability for the spatial distribution of vegetation CUE in Qingzang Plateau, Hengduan Mountains and other topographically complex areas. In general, before applying the CMIP6 models for regional vegetation CUE simulation, it is necessary to comprehensively evaluate the specific models from multiple perspectives to select the models with better simulation performance.

Forests are crucial terrestrial ecosystems with wide distribution and substantial biomass, playing a vital role in the global carbon cycle. The estimation of aboveground biomass (AGB) in forests serves as a significant indicator of ecosystem productivity and is pivotal for studying material cycles and global climate change. Traditional methods for AGB estimation rely on individual tree-scale or forest stand-scale tree physical structural information measurements, which are often time-consuming and labor-intensive to obtain. Remote sensing technology offers a solution for comprehensively and multi-temporally obtaining forest structural information in large scale, making it indispensable for forest AGB estimation. Therefore, it is important to review and summarize recent advancements in remote sensing techniques for estimating forest AGB to promote their application and guide the development of related industries. This paper presents a comprehensive overview of the principles and methods used for estimating forest AGB using optical data, synthetic aperture radar (SAR) data, and light detection and ranging (LiDAR) data. It also analyzes the current status of synergistic estimation of forest AGB using multiple remote sensing data sources. The study highlights three key findings: (1) The use of novel remote sensing data, such as high-resolution satellite imagery and Global Ecosystem Dynamics Investigation LiDAR data, is expanding the boundaries of spatial and temporal resolutions, providing enhanced data sources for forest AGB research. (2) Synergistic approaches that combine multiple remote sensing data sources show promise in improving the accuracy of forest AGB estimation, but further optimization of related models is needed. (3) Machine learning, artificial intelligence, and deep learning techniques have been widely applied in forest AGB estimation, but continuous research on remote sensing mechanisms remains essential for innovation. Improvements in models and methodologies should revolve around a better understanding of these mechanisms.

There are substantial carbon exchange fluxes among soil, vegetation and atmosphere in the terrestrial ecosystems, which are highly relevant to global climate changes. Mycorrhizal fungi can form symbiotic associations with most terrestrial plants, linking the above- and below-ground ecosystems through mineral nutrient-carbon exchange; thus, mycorrhizal fungi play crucial roles in terrestrial carbon cycling. This review summarized the involvements of mycorrhizal fungi in the terrestrial carbon cycling processes, including the carbon input, and formation, stabilization, and decomposition of soil organic matter. Studies have demonstrated that mycorrhizal fungi markedly influence the terrestrial carbon input processes by alleviating plant nutrient deficiencies, improving plant stress resistance, influencing plant photosynthesis, and regulating plant diversity-productivity relationships, subsequently sustaining or improving primary productivity of terrestrial vegetation. A considerable proportion of photosynthetic carbon is channeled directly into the soil matrix via the fungal mycelial network, where it is partly converted into microbial-derived organic carbon, further changes the composition of soil organic carbon, and be stabilized through association with minerals and/or forming soil aggregates. Mycorrhizal fungi can affect the decomposition and transformation of soil organic matter mainly through two mechanisms: the rhizosphere priming effects and/or hyphosphere biogeochemical processes. These mechanisms involve the secretion of specific extracellular enzymes, shaping hyphosphere microbial communities, induction of chemical oxidation, and competition for limited resources (e.g., nutrients and water) with free-living saprotrophs. Considering the sensitivity of mycorrhizal fungi to environmental and climate changes, we also discuss the impact of global change factors on soil carbon cycling mediated by mycorrhizal fungi. Finally, we proposed future research directions, emphasizing a need for in-depth studies on the role of mycorrhizal fungi in terrestrial carbon cycling and their environmental dependence based on network experiments in typical ecosystems. Quantitative studies should be strengthened to integrate mycorrhizal fungi into ecosystem carbon cycling models, and mycorrhizal technologies should be developed and practiced in ecological restoration and agriculture to facilitate terrestrial carbon sequestration for achieving the national carbon neutrality goals and combating climate changes.

Root exudates play an important role in soil carbon balance, acting as an important medium for material and energy exchange and information transfer between plant roots and soil, and also the crucial forms for plant response to environmental changes. Frequent extreme drought events accompanied with global climate change have imposed a profound impact on both above- and below-ground plant growth processes. However, significant limitation exists in understanding the responses of root exudates and their mediated rhizosphere priming effect to drought due to the complexity of root-soil interface interactions and the limitation in devices and methods for collecting root exudates. This paper reviews the effects of drought on the quantity and quality of plant root exudates, with emphasis on the rhizosphere priming effect mediated by root exudates under drought stress. The future research focuses on root exudates was also discussed. This study will provide suggestion for soil carbon sink assessment under the future climate change.

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 Leaf litter and root input are two major resource of soil organic carbon (SOC) accumulation. Quantifying the effects of leaf litter and root removal on SOC pool and its multiple components has implication for understanding the mechanisms of SOC stabilization in forest ecosystem.

Methods Based on a long-term (12 years) litter removal experiment including control (CK), leaf litter removal (NL), root removal (NR), and both leaf litter and root removal (NLR) that conducted in Hunan Huitong Forest Ecosystem National Field Scientific Observation and Research Station, Chinese Academy of Sciences, we compared the relative importance of leaf litter and root removal on multiple components of SOC pool in a subtropical Cunninghamia lanceolata plantation in different season.

Important findings Although leaf litter and root removal both reduced SOC content, the relative contribution of leaf litter and root removal on multiple SOC components were different. Specifically, the NL reduced more SOC, soil mineral-associated organic carbon (MAOC), heavy fraction organic carbon (HFOC) and readily oxidizable carbon (ROC) contents than NR and NLR. While, the NR decreased more soil particulate organic carbon (POC) content than NL and NR. In contrast, the NLR had more negative effect on light fraction organic carbon (LFOC) content than other two treatments. Correlation analysis and redundancy analysis showed that SOC components contents were positively correlated with soil total nitrogen content and carbon to nitrogen ratio. Besides, seasonal variability had significant effects on POC, LFOC contents, and their contribution of multiple carbon components to SOC. Moreover, the correlation between SOC component contents and total phosphorus content and carbon to phosphorus ratio was enhanced in winter compared with summer. Taken together, our study provides new evidence for the long-term effects of long-term litter removal on SOC and its multiple components in Chinese fir plantation, which has implications for predicting the response and feedback of SOC accumulation to global changes.

Aims To reveal the relationship between rhizosphere microbial composition, functional characteristics and health status of Malania oleifera.

Methods We collected rhizosphere soil samples of healthy and non-healthy M. oleifera at five different habitats in broadleaf forest, artificial planting forest and karst forest, sequenced the microbial communities using illumina high-throughput sequencing techniques and predicted the microbial community functions using FAPROTAX.

Important findings The results showed that: 1) Amplicon sequence variants (ASV) representative sequence classification analysis showed slight differences in microbial composition among five habitats. The top five bacterial phyla were Acidobacteriota, Proteobacteria, Actinobacteriota, Chloroflexi and Myxococcota. There were significant differences in rhizosphere microbial composition between healthy and non-healthy plants, and the dominant microbial taxa changed significantly. 2) The non-metric multidimensional scaling (NMDS) analysis showed significant differences in microbial components of M. oleiferawith different health status. Redundancy analysis results showed that the healthy plant samples were distributed along the first axis, and the two axes explained 25.83% of the variation in the microbial community as a whole. The contents of soil available phosphorus, total potassium and pH were the main factors affecting the rhizosphere microbial communities of healthy plants. Redundancy analysis of non-healthy plants showed that 51.84% of the variation in microbial community was explained by the two ordination axes. Soil total potassium content and available phosphorus content represented the important factors affecting the rhizosphere microbial communities of the non-healthy plants. 3) The correlation heatmap showed that soil pH, available phosphorus content and total potassium content were significantly correlated with the abundance of Chloroflexi, Planctomycetota, Methylomirabilota and Desulfobacterota in healthy plants. However, the abundance of Desulfobacterota, Acidobacteriota, Desulfobacterota, Latescibacterota and Gemmatimonadota were significantly affected by soil pH, available nitrogen content, available phosphorus content, total phosphorus content and total potassium content in non-healthy plants. 4) FAPROTAX functional prediction results showed that the abundance of phototrophy, photoautotrophy, aromatic compound degradation, cyanobacteria and oxygenic decreased significantly in healthy rhizosphere microorganisms, whereas fermentation, ureolysis and human pathogens increased significantly. The results demonstrate that the rhizosphere microbial community undergoes significant changes in different health conditions.

For many plants, nectar is hidden in the depth of nectar spurs. The diverse morphology and length of nectar spurs can attract pollinators with various proboscis lengths and promote the differentiation of pollination niche, which plays an important role in the formation of species diversity. Therefore, nectar spur is considered as a key innovation trait in promoting speciation and an ideal trait for studying floral evolution and plant-pollinator coevolution in angiosperm. This review systematically summarizes the worldwide plant taxonomic databases and published articles, classifies the nectar spur plants, and reviews the diversity and evolutionary mechanisms of nectar spur plants. We investigated 3 427 nectar spur species belonging to 13 orders, 23 families and 271 genera of angiosperm. Among them, Orchidaceae has the largest number of species, with 1 536 species, following by Papaveraceae with 487 species, Ranunculaceae with 351 species, Balsaminaceae with 284 species and Violaceae with 197 species, accounting for 83.3% of all the species. According to the sources of the development of nectar spurs, the nectar spurs can be divided into six types: petal spur, corolla spur, sepal spur, calyx spur, tepal spur and hypanthium spur. The petal spurs are the predominant type, detected in 212 genera. The average length of nectar spurs in Balsaminaceae is the longest (23.8 mm) among the 2 546 species whose nectar spurs have been measured. The shortest nectar spurs are reported in Lycelandaceae, which are only 1.6 mm on average. Most nectar spurs have different degrees of curvature, likely helping to improve the pollination efficiency. The number of nectar spur(s) in a flower ranges from 1 to 6, and most species have only one nectar spur in a flower. Multiple nectar spurs may increase the visiting time of pollinators. Some plants in Orchidaceae and Violaceae have appendages inside the nectar spurs, which may have the function of nectar secretion. The pollinators of plants with nectar spur mainly comprise insects from Hymenoptera, Lepidoptera, and some long-proboscis species from Diptera and birds. Nectar robbers are mainly bees and birds. There is a general association of geographic mosaic theory of coevolution between the length of nectar spur and the length of pollinator proboscis. Evolutionary ecologists have proposed the hypothesis of “Darwin’s Mechanistic Model” and “The Pollinator Shift Model” to explain this phenomenon. In future studies of the mechanisms of nectar spur evolution, we should not only focus on the morphological characteristics of spur length and proboscis length and the pollination ecology, but also explore the driving forces of nectar spurs evolution from cell division/elongation, functional genes, abiotic factors, with the help of novel technological approaches including developmental anatomy and genomics.

Aims The dynamic monitoring of basin-scale land use and land cover changes and carbon stock estimation of the terrestrial ecosystem can provide suggestions for optimizing land utilization, enhancing terrestrial ecosystem carbon storage, and achieving the “dual carbon” objective.

Methods Based on the Landsat 5 TM and Landsat 8 OLI images from 1986 to 2022, this study employed random forest to obtain ten land use and land cover maps of the Songhua River Basin with high accuracy and conducted dynamic monitoring of land use and land cover change and its ecosystem carbon storage using an integrated valuation of ecosystem services and trade-offs (InVEST) model, Mann-Kendall tests, and Theil-Sen median trend analysis.

Important findings Results showed that farmland has the largest area in the basin, followed by forest land, grasslands, unused lands, water, construction land, sparse forest land, and shrub land. Among them, farmland, forest, and grassland are the dominant land use types in the study area. During the 1986-2022 period, the farmland expanded by 11 462.68 km² while forest land decreased by 18 567.21 km²; the construction land experienced the most significant change rate of 5.3% with an increased area of 3 505.82 km²; the change rate of the sparse forest is 4.7%, ranking second after construction land but having minimal impact on the overall basin due to limited area changes. The change rate of unused land was 4.5%, with an increased area of 5 385.43 km². There was evident spatial heterogeneity in the distribution of the terrestrial ecosystem carbon stocks within the Songhua River Basin, with high carbon stocks predominantly found in Da Hinggan Mountains and Xiao Hinggan Mountains as well as the Changbai Mountains. The median carbon stock values were observed in the Hinggan League, Songnen Plain, and Sanjiang Plain. In contrast, the areas with low carbon values were observed in Daqing and Baicheng. Over the 36 years, there was an overall decline in carbon storage within the basin, primarily concentrated in the regions initially characterized by high carbon stock values. However, the area with increased carbon stock is scattered in the basin. Notably, three recovery instances of ecosystem carbon stock occurred in 1994, 2002, and 2018 within the Songhua River Basin, all related to the changes in forest land. Based on ensuring no reduction of current forest land, it is recommended to expand forest land and continue implementing forestry projects to effectively prevent further depletion of terrestrial ecosystem carbon storage in the Songhua River Basin.

Aims Gynaikothrips uzeli is a major quarantine pest attacking Ficusplants. To seek effective and sustainable methods to control the pest, it is necessary to assess its host preference among different Ficusspecies and understand the critical factors of this behavior.

Methods In this study, the behavioral preference of G. uzeli to volatile organic compounds (VOCs) of three potted Ficusspecies were evaluated. The VOCs released by the three Ficus species were analyzed using GC-MS, and the major compnents were used to test the pest preference. Based on the transcriptome analyses, we inferred the key genes that affect the biosyntheses of those VOCs.

Important findings Behavioral preference of G. uzeli to the VOCs of the three Ficusspecies is F. benjamina > F. microcarpa > F. elastica.The behavioral preference of G. uzeliwas significantly positively related to the relative content of β-cyclocitral, β-maaliene, β-copaene, and significantly negatively related to the relative content of trans-α-bergamotene. A significantly positive relationship was found between the relative content of β-cyclocitral and the expression of gene Fm.09G0004550 (CCD4). Moreover, the relative content of β-maaliene was significantly positively related to the expression of gene Fm.newGene1857(STPS) and Fm.newGene6827 (VIT_19s0014g04930). The relative content of β-copaene was significantly positively related to the expression of gene Fm.11G0000860 (LUP2) and Fm.newGene1857 (STPS). The relative content of trans-α-bergamotene was significantly positively associated with the expression of gene Fm.13G0003820 (LUS1) and Fm.newGene489 (GgbAS1). The above findings suggest that four terpenes (β-cyclocitral, β-maaliene, β-copaene and trans-α-bergamotene) determine the behavioral preference of G. uzeli to Ficus plants, and their biosyntheses might be mainly affected by six terpene synthase genes (Fm.09G0004550, Fm.11G0000860, Fm.newGene1857, Fm.newGene6827, Fm.13G0003820 and Fm.newGene489).

Caryopteris mongholica is a key protected wildflower plant distributed in typical steppe, desertified steppe and desert areas. But there is a lack of research on its community characteristics and classification. This paper aims to study the distribution, characteristics and classification of C. mongholica in northern China and provide a reference for further protection and management. From 2018 to 2021, a total of 40 representative C. mongholica sites were selected in northern China, and their community characteristics were studied using the sample plot survey method. Results showed: (1) Caryopteris mongholica is concentrated in the eastern, central and western of Nei Mongol Plateau, the northern Loess Plateau, Hexi Corridor, Qilian Mountains and other northwest temperate desert or steppe areas in China, and is often the dominant or associated species in the communities. (2) According to the survey of 40 sample sites, a total of 149 species of seed plants were recorded, belonging to 107 genera of 37 families, among which 31 communities with C. mongholica as construction or dominant species and 140 species of seed plants were recorded, mainly Compositae, Leguminosae and Gramineae. Among them, 39 species were shrubs, dwarf- and semi-shrubs, 76 species were perennial herbs and 24 species were annuals and biennials. In the classification of species presence, 87.94% were occasional species with frequency distribution less than 20%. Wide-range xerophytes occupied the advantage (63.12%) in the water ecological types. Middle Asia elements (26.24%) were the major floristic geographic elements. (3) Based on the life form and dominance of species, the 31 C. mongholica communities were divided into 3 association groups, C. mongholica - herb association group, C. mongholica + shrub - herb association group and C. mongholica + shrub association group, which were further subdivided into 19 associations. (4) Longitude and annual precipitation significantly influence the distribution of C. mongholica communities and species diversity.

Aims The region around the South China Sea is a relatively independent semi closed geographical unit, which can be divided into eight areas, including the coast of South China, Hainan Island, Taiwan Island, Indo-China Peninsula, Malay Peninsula, Kalimantan Island, Palawan Island, and Luzon Island. The region around the South China Sea is one of the regions with the most concentrated distribution of mangrove plants in the world. This study aims to explore the geographical distribution pattern and the underlying mechanisms of mangrove species in the eight regions around the South China Sea.

Methods Species richness and distribution of mangrove in the region around the South China Sea and other regions worldwide were obtained through extensive literature survey and mapped with ArcGIS. Species distribution map with 1° × 1° grid of four typical mangrove taxa, i.e. Rhizophoraceae, Malvaceae, Sonneratia, Avicennia, were drawn by DIVA-GIS 7.5.0. The migration history and route and its main influencing factors were explored through literature survey in ISI Web of Science.

Important findings (1) There are 39 species of true mangroves and 14 species of semi-mangroves distributed in this region, mostly distributed in Malay Peninsula, Kalimantan Island, Hainan Island, Indo-China Peninsula, Luzon Island. (2) All mangrove species are widespread in the region, which may be caused by the fact that South China Sea has completely different ocean current and monsoon directions in summer and winter, promoting the long-distance dispersals of mangrove plants. (3) There is a certain internal circulation in the northern and southern parts of the South China Sea, and resulting in the appearance of relatively isolated genetic lineages on both sides of the line connecting Cam Ranh Bay and the northern tip of Palawan Island, especially for the true mangroves such as Excoecaria agallocha, Lumnitzera racemose and Aegiceras corniculatum. (4) The sea level decreased by about 120 m during the Pleistocene, which profoundly affected the distribution pattern and migration route of mangroves in the region. In the future, phylogeographical studies using updated molecular technology, especially genomic data, is suggested to explore the dispersal history of mangrove plants and their future evolutionary trend under global climate change.

Forest size structure (the diameter distribution of trees in a forest) is a comprehensive indicator of forest demographic processes. It is the basis for determining forest successional stage and the state of forest health, estimating forest biomass and predicting forest carbon sink potential. Studies of forest size structure began with statistical descriptions before progressing to theoretical and mathematical deduction. In early statistical studies of forestry, many common probability distribution functions were used to fit plot-scale variations in size structure, but most of these functions were not derived from biological processes and therefore lack clear biological meaning. With the development of macroecology, the principle of maximum entropy and the central limit theorem have been used to explain the relatively consistent forest size structure at large spatial scales. Such models mainly focus on probabilistic statistics rather than ecological processes. Reports of a power-law size structure in natural mature forests in the early 2000s spawned a series of theoretical studies, including metabolic scaling theory and the theory of gap succession, among others. These theories have proposed that the observed power-law size structure results from the relationship between tree size and resource use on the individual scale and tree competition for resources on the community scale. Demographic equilibrium theory provides a general framework for analyzing the relationship between the steady state forest size structure and tree growth and mortality. Under this equilibrium framework, the hypothesis of demographic optimality further provides a new perspective for the analysis of forest size structure. Mathematical models including transition matrices, integral projections, and partial differential equations are powerful tools for analyzing forest size structure dynamics. However, due to the difficulty of identifying time-varying solutions to the mathematical models, most studies have been confined to the framework of forest demographic equilibrium. To understand dynamic variations of forest size structure and predict forest carbon sink potential in a rapidly changing climate, it is essential both to find general time-varying solutions to the mathematical models and to tighten empirical constraints on the effects of climatic factors on forest growth and mortality rates.

Aims Due to complex root-soil interactions, the responses of carbon (C) dynamics in the rhizosphere soil to nitrogen (N) deposition may be different from those in bulk soil. However, the potentially different responses of C dynamics between the rhizosphere and bulk soil and their contributions to soil C sequestration under N deposition are still not elucidated.
Methods In this study, a typical subalpine coniferous plantation (Picea asperata) with chronic N addition treatments in southwestern China was selected as the research object. Based on the experimental plots of simulated N deposition (control: 0 kg·hm^-2·a^-1; N addition: 25 kg·hm^-2·a^-1), we measured the contents of soil organic carbon and its different physical and chemical fractions. Afterwards, by combining the rhizosphere spatial numerical model, we explored the differences in the C pool size of SOC and its fractions and their relative contribution to SOC pools between the rhizosphere and bulk soil, and further quantified the effects of N addition on soil C sequestration in rhizosphere soil.
Important findings The results showed that: 1) Although the addition of N increased the content of SOC and its physical and chemical components in the rhizosphere and non-rhizosphere at the same time, it only reached a significant level in the rhizosphere. Specifically, the rhizosphere SOC content increased by 23.64% under N addition, in which particulate organic carbon (POC), mineral-associated organic carbon (MAOC), labile carbon (LP-C) and recalcitrant carbon (RP-C) content increased by 19.63%, 18.01%, 30.48% and 15.01%, respectively. 2) The total SOC pool increment of spruce forest (0.88 kg·m^-2) was verified with the results of the rhizosphere space numerical model, and the effective rhizosphere extent of the southwest mountain coniferous forest was estimated to be 1.6 mm. Within this extent, N addition increased the SOC stocks of the rhizosphere and bulk soil by 33.37% and 7.38%, contributing to 45.45% and 54.55% of the total SOC pool increment, respectively. Among them, labile C components (POC and LP-C) are the major contributors to rhizosphere SOC accumulation under N addition. These results suggested that the rhizosphere and bulk soil of coniferous forest in southwestern mountainous area had great C sequestration potential under N deposition, and the C sink was more obvious in the rhizosphere soil. Our results highlight the importance of integrating rhizosphere processes into land surface models to accurately predict ecosystem functions in the context of increasing N deposition.

Arid and semi-arid ecosystem areas, which constitute an important component of the global land surface, act to regulate the long-term trend and interannual variations in global carbon and water cycles. Previous studies on the mechanisms underlying ecosystem carbon and water cycling and the development of relevant data products focus primarily on forest, grassland, and cropland ecosystems, with few research attention given to semi-arid shrublands. This research gap hinders the evaluation and projection of ecosystem functions at the regional scale. Since 2011, we used the eddy covariance technique to make continuous in situ measurements of carbon, water and heat fluxes in a shrubland ecosystem at Yanchi Research Station, the Mau Us Sandy Land. Data processing steps mainly included data collection, post-processing of raw data, quality control, gap-filling and carbon flux partitioning. We produced flux and micro-meteorological datasets at half-hourly, daily, monthly, and annual temporal resolutions for the years 2012-2016, and analyzed the overall quality of the datasets in terms of the proportion of valid data and the energy balance closure of flux measurements. Results showed: (1) After quality control, the proportion of valid data for half-hour net ecosystem CO₂ exchange (NEE), latent heat flux (LE), and sensible heat flux (Hs) was 56.23%-62.19%, 79.40%-94.12%, and 77.56%-91.27%, respectively. (2) Annual and monthly energy balance ratio ranged 0.78-0.83 and 0.59-1.19, respectively. (3) The energy balance closure estimated using the “ordinary least squares” regression method showed that the interannual and seasonal variations in the slope of regression curves varied with a range of 0.73-0.79 at interannual scale and 0.73-0.92 at seasonal scale, respectively. These results indicate that our datasets have a high proportion of valid data and a reasonable energy balance closure, and thus can be used in studies related to ecosystem processes and functions at varing spatio-temporal scales.

Aims The aim of this research was to clarify the effects of intercropping and inoculation with arbuscular mycorrhizal fungi (AMF) on carbon transport and phosphorus uptake in black locust (Robinia pseudoacacia) and konjac (Amorphophallus konjac). The results could provide empirical evidence to reveal the mechanisms of black locust intercropping for disease control and plant growth promotion of konjac, and popularize the green and high-yielding cultivation technique of konjac under black locust.

Methods The experiment was carried out in two-compartment rhizoboxes separated by a 25-μm nylon net, each of which comprised compartment A (non-inoculated or AMF-inoculated black locust) and compartment B (monocropped black locust or intercropped konjac). A ¹³C stable isotope labeling technique was used to label the leaves of black locust in compartment A with ¹³CO₂. Carbon transport from black locust to konjac and the effects of AMF colonization on agronomic traits, ¹³C abundance, and phosphorus content in both crops were investigated.

Important findings The result showed that: (1) After inoculation, the AMF infection rate of black locust and konjac plants by hyphal links in compartment B reached 47.1% and 60.4%, respectively. For black locust, this AMF infection rate was 14.1% lower than that of directly inoculated plants under monocropping. In the case of intercropping, the biomass (dry mass) of AMF-inoculated konjac plants was 9.7% (aboveground parts) and 36.2% (belowground roots) higher than that of non-inoculated plants. (2) Compared with the non-inoculated plants under monocropping, the carbon fixed by photosynthesis of black locust plants in other treatments (non-inoculated + intercropping, inoculated + monocropping, and inoculated + intercropping) was mainly allocated to the plant roots and rhizosphere soil in compartment A, and more carbon passed through the nylon net in the form of root exudates to reach the rhizosphere of neighboring crop plants. (3) Compared with the respective non-inoculated controls, AMF inoculation in the monocropping and intercropping systems prominently improved phosphorus contents in the leaves, stems/petioles, roots, and total plants of black locust and konjac in compartment B. The findings suggest that AMF colonization could facilitate carbon transport from black locust to the rhizosphere soil and plant tissues of konjac. Intercropping konjac with black locust is an effective practice to promote AMF colonization and phosphorus uptake by both host plants.

Aims The purpose of this study is to examine the responses of litter decomposition to nitrogen (N) deposition and aboveground litter manipulation.
Methods A two-factor experiment of N addition and litterfall manipulation was performed in a N saturation evergreen broadleaf forest on the western edge of the Sichuan Basin in China from June 2014 to June 2019. We conducted three levels of N addition, including an N control (CK, ambient N input), low N (LN, 50 kg·hm^-2·a^-1) and high N (HN, 150 kg·hm^-2·a^-1), and three levels of litterfall manipulation, including intact litter input (L0, no litter alteration), litter reduction (L-, reduced by 50%) and litter addition (L+, increased by 50%).
Important findings We found six-year N addition did not significantly alter the aboveground litter input in the studied forest ecosystem. N addition significantly inhibited leaf litter decomposition, with the leaf litter decomposition significantly decreased in high N treatment. N addition significantly reduced the remaining rate of manganese (Mn) in the late stage and promoted the release of Mn. Litter manipulation did not significantly alter the rate of leaf litter decomposition, but increased the remaining rate of Mn in the litter and slowed down the release of Mn. There was no significant interactive effect between N addition and litter manipulation. This study showed that N addition affected litter decomposition in subtropical N-saturated evergreen broadleaf forests by directly affecting litter decomposition, while litter manipulation mainly affected the content of Mn during litter decomposition. Therefore, the content of Mn of litter may play a key role in the process of litter decomposition in response to N input.

Fine roots are the most active and sensitive part of the root system, and play an important role in the biogeochemical cycles of forest ecosystems. Fine root growth and turnover have a strong impact on the root carbon flux into soil. The effect of global warming on below-ground ecological processes has become a hot issue in global change research, and the response of fine root dynamics to warming will directly affect the carbon balance of forest ecosystems. In this paper, the effects of warming on fine root production, mortality, biomass and turnover are reviewed to reveal the effects of warming on fine root dynamics. Generally, warming affects the fine root production and mortality by changing soil moisture, nutrient availability and distribution of recent photosynthetic products, accelerates fine root turnover process, and then reduces fine root biomass. However, fine root growth is affected by many factors, making the research results of the impact of warming on fine roots inconsistent among different studies, due to the difference in tree species, regions, warming methods and other factors. Therefore, comprehensively analyzing the response of forest fine roots under warming is very important for studies on below-ground ecological processes. In the future, we call for more research in the following aspects: (1) according to the advantages and disadvantages of each warming method, compare the effects of different warming methods and warming durations on the growth dynamics of fine roots and above-ground parts; (2) combined with various fine root observation and experimental methods, comprehensively analyze the effect of warming on fine root growth dynamics, and strengthen the research on the effect of warming on fine root order structure; (3) strengthen the research on the interaction of warming and nutrient, water and CO₂ on fine root growth dynamics; (4) focus on the effects of warming on fine root dynamics in different soil layers, especially in deep soils; and (5) deeply study the potential response of the relationship among fine roots, soils and microorganisms to warming.

The alteration of terrestrial carbon cycling under climate warming is regulated by soil organic carbon (SOC) dynamics. Previous studies have developed multiple warming methods, mainly including laboratory incubation experiment, field in-situ manipulative experiment, and temperature gradient sampling, to investigate the responses and mechanisms of SOC dynamics to climate warming. However, due to the methodological limitations, the studies on the effect of warming on SOC dynamics cannot lead to consistent conclusions. SOC dynamics mainly include two processes: carbon input and carbon decomposition, and are also regulated by carbon persistence. The changes of carbon input, carbon decomposition, and carbon persistence together determine the response of SOC dynamics to warming. Previous studies showed that both carbon input and decomposition may positively respond to warming, which is related to the enhanced activities of plants and soil microbes. However, some studies pointed out that warming-induced alterations of soil physical and chemical properties (e.g., the decrease of soil water content) and biological processes (e.g., microbial community thermal adaptation) may affect the responses of carbon input and decomposition to warming. Moreover, inconsistent responses may arise when focusing on the SOC responses to warming in top (0-30 cm) or deep (>30 cm) soils due to the limitations of environmental factors on carbon input and decomposition in deep soils, as well as the different persistence of SOC in deep soils compared to top soils. Future research should focus on developing new warming methods, increasing research on deep soils and climate-sensitive ecosystems, introducing new technologies to study the source, structure, and protection of soil organic matter, paying attention to the response of plant-soil animal-soil microbe system to warming and its regulation on SOC dynamics, to improve uncertainties in carbon cycle models and more accurately predict the feedback of the global carbon cycle to climate warming.

Aims Soil respiration is one of the most critical components of carbon cycle in terrestrial ecosystems. The study on temporal dynamics of soil respiration and its linkage with environmental factors in desert steppes under changing precipitation can provide data supports for a deep understanding of the regulatory mechanisms of key carbon cycling processes in fragile ecosystems.
Methods A field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural, 30% increase, 50% increase) was set up in 2014 in a desert steppe in Ningxia. The temporal dynamics of soil respiration rate were explored during the growing season (from June to October) in 2019, and the relationships between soil respiration rate and soil properties and plant characteristics were analyzed.
Important findings Soil respiration rate showed a seasonal variation of an increasing and a decreasing trend across the growing season, with the maximum values (2.79-5.35 μmol·m^-2·s^-1) occurring in late July or early August. Compared with the natural condition, 30% reduction in precipitation did not result in a significant effect on soil respiration rate, reflecting the adaptability of soil respiration to moderate drought. Overall, 50% reduction in precipitation reduced soil respiration rate, whereas increased precipitation (especially the 30% increase) enhanced soil respiration rate, and this positive effect was especially obvious in the early growing season (June to July). Soil respiration rate had a significantly exponential relationship with soil temperature and a significantly linear relationship with soil water content. Soil physicochemical property had a highly independent explanatory power for soil respiration rate (R² = 0.36), and its effect was highly correlated with soil biological property and plant diversity (R² = 0.31). Precipitation could affect soil respiration rate either directly or indirectly through the influences on soil biological property and plant biomass. The results indicated that a moderate increase in precipitation could accelerate soil respiration by alleviating soil water limitation, stimulating soil enzyme activity, promoting microbial activity and plant growth in the desert steppe, and that an extreme increase in precipitation would lead to a decrease in soil permeability and a hindrance to microbial metabolic activity, thus inhibiting soil respiration.

Aims In the past 40 years, Qingzang Plateau has experienced rapid warming, and its air temperature is projected to continue to rise in the next few decades. Since climate warming may alter soil moisture and nutrient availability, understanding how these changes affect the responses of alpine grasslands to increasing air temperature is therefore crucial to accurately anticipate the shift in vegetation productivity of alpine grassland ecosystems under future warming.

Methods The aboveground biomass of plant communities and four functional groups (legumes, grasses, sedges, and forbs) in alpine grasslands were measured at the field experiments of warming, fertilization (nitrogen, phosphorus) and their interactions across three altitudes (3 200, 3 700 and 4 050 m).

Important findings 1) We found significantly positive correlation of the warming response ratios with altitude. 2) Warming resulted in the increase of aboveground biomass at middle and high elevation; moreover, under the condition of N, P addition, warming significantly increased aboveground biomass at three altitudes. 3) The responses of relative biomass of four functional groups to warming at different altitudes were inconsistent. Even within the same functional group, they showed significant different responses to warming due to the distinct nutrient conditions across the altitudes. Taken together, our results suggest that the responses of alpine grasslands to warming were altitudes-dependent, which was also modulated by soil nutrient availability.

Aims Precipitation regime alteration and increasing nitrogen deposition have substantially altered the structure and function of grassland ecosystems. However, the responses of stoichiometry in soil and vegetation remain elusive, which limits the accuracy in predicting functional changes of alpine meadow.

Methods Based on a manipulation experiment platform of nitrogen addition (10 g·m^-2·a^-1) and precipitation change (precipitation reduction by 50% and increase by 50%) in an alpine meadow on the southern foot of Qilian Mountains, organic carbon (SOC), total nitrogen (SN), total phosphorus (SP) contents in topsoil (0-10 cm), and foliar carbon (LC), nitrogen (LN), phosphorus (LP) and potassium (LK) contents of dominant plant species, including Gentiana straminea, Elymus nutans, Oxytropis ochrocephalaand Kobresia humilis,were continuously surveyed from 2017 to 2020.

Important findings The soil stoichiometry varied significantly among different years, but was not affected by experimental treatments. The aboveground plant biomass showed inter-annual variations and was significantly affected by nitrogen addition. The responses of leaf stoichiometry were species-specific. Foliar stoichiometry of a resource-conservative species, E. nutans, showed limited variations, while that of the sensitive species, K. humilis, fluctuated significantly. To exclude the impacts of temporal variations, we conducted the analysis based on the relative changes (Δ) between treatment plots and the control plots from the same year and the results showed that nitrogen addition significantly increased ΔPB by 15.6%. Precipitation reduction significantly decreased ΔLC of O. ochrocephala by 6.8% while increased ΔLP of K. humilis by 19.8%. Our findings suggest that only nitrogen addition increased aboveground biomass and precipitation reduction altered LC and LP contents in some plant species. The temporal or species-specific effect, rather than experiment treatments effect, dominated the stoichiometric variations of soil and vegetation, highlighting the complex responses of alpine meadow to precipitation regime alteration and nitrogen addition.

Aims Trait-based methods have provided a new viewpoint for predicting community dynamics. We use these approaches to reveal how functional traits influence the key demographic rates of plant species, thereby improving our understanding of community dynamics.

Methods We monitored the growth and mortality rates of 26 common woody plant species from Dajinshan Island, Shanghai, over a five-year period (2016-2021). Nine leaf and wood traits related to competition and utilization strategies for light, water and nutrient resources were measured. Then, the relationships between the relative growth and mortality rates and each of individual trait, as well as the multi-trait synthesized plant economics spectrum, were analyzed.

Important findings Our results showed that leaf area and leaf nitrogen content were significantly and positively correlated with the relative growth rate, while leaf thickness, twig wood density and leaf dry matter content were significantly and negatively correlated with the relative growth rate. Stem wood density and twig wood density were significantly negatively correlated with the relative mortality rate. The plant economics spectrum that is formulated by nine traits, could explain 32.8% variation in relative growth rate; however, it did not correlate with the relative mortality rate. The relative growth was higher for acquisitive species than that for conservative species. Our results suggest that plant functional traits are important in affecting their growth, and that plant economics spectrum can accurately predict variations in relative growth rates among species, but its predictions for relative mortality are weaker.

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.

Fossil pollen and spore records provide highly creditable proxy data to investigate the past environmental changes such as palaeovegetation and palaeoclimate. Pollen database promotes past environmental studies from local to regional and global scales and from qualitative to quantitative reconstructions. This is of great significance on exploring the interactions among past vegetation, climates and anthropogenic disturbances at large spatial scale and long temporal scale, to better understand the evolution of the earth system. In this paper, a fossil pollen dataset of China is compiled, by synthesizing 372 original or digitized fossil pollen records including 790 pollen taxa in China’s land and ocean during the late-Quaternary (since 50 ka BP). The dataset includes site names, latitude, longitude and altitude, pollen data source, sample type, sediment length or span, sample number of each site, dating method and dating number, age span and reference, as well as the fossil pollen percentage of each sampling site. The pollen data, mostly published from late 1980s to present, are concentrated in vegetation regions of temperate and subtropical forests, temperate grasslands, temperate deserts and alpine vegetation on the Qingzang Plateau. Sample sites are distributed at different altitudes from deep sea to high Qingzang Plateau, but the majority of the sites are located between 0-2 000 m. The dataset comprises of 178 raw pollen records (47.8%) and 194 digitized pollen records (52.2%). Pollen samples are mainly from lake sediment (151 sites), alluvial/fluvial sediment (99 sites), and peat (67 sites), accounting for 85.2% of the total sampling sites. Radiocarbon is the main dating method that accounts for 93.8% of total samples, and most of the sites have 2-10 radiocarbon dating data. Each site has an average number of pollen taxa of 19, with the most sites having 4-30 pollen taxa. The temporal and spatial distribution of representative pollen taxa (Pinus, Quercus, Artemisia and Poaceae) reveals increasing trends both in their distributional range and pollen concentration from the last glacial maximum to Holocene, but such trends have various regional patterns in different parts of China. This fossil pollen dataset is a fruitful work of collection of pollen records in most territory of China that conducted by palynologists from China and overseas during the last half century. It consolidates the valuable and fundamental data that can be potentially utilized to explore the evolution of past environments and their driving mechanism of climate change and human disturbance.

Aims Understanding the effects of shrub encroachment on plant and soil microorganisms in the forest-grassland ecotone will help improve the understanding and management of shrub encroachment in the forest-grassland ecotone.

Methods In this study, different levels (light, moderate and heavy) of shrub encroachment were selected in the forest-grassland ecotone of Dongling Mountain Nature Reserve in Beijing, to explore the effects of shrub encroachment on plant diversity, soil microbial diversity, plant individual trait and soil nutrients by plot method and high-throughput sequencing technology. The correlation between plant diversity, soil microbial diversity, plant individual trait and soil nutrients were also developed in order to further explore the effects of shrub encroachment on plants and soil microorganisms and associated mechanisms.

Important findings Our results showed that: 1) Shrub encroachment significantly reduced the diversity of plants with the different responses of arbor, shrub and herb, among which the diversity index of herb plants decreased in the largest level. 2) Shrub encroachment significantly increased the diversity of soil fungal microorganisms. 3) Shrub encroachment significantly increased the height and crown width of shrubs, while soil total nitrogen and organic carbon contents increased significantly with the increasing shrub encroachment level. 4) The partial least squares path model (PLS-PM) revealed that shrub encroachment had a direct impact on plant and soil microorganisms, whereas plant individual trait and soil nutrients did not have a direct impact on them. The redundancy analysis (RDA) further showed that shrub height made great contribution to the interpretation of changes in plant diversity, and soil total nitrogen content was the main factor in affecting soil microbial diversity. There was a stronger correlation of soil fungal microbial diversity with plant diversity than its relationship with soil bacterial microbial.

Aims Leaf temperature is one of the important microenvironmental parameters for energy exchange and physiological processes of plants. Leaf thermal traits can regulate leaf temperature so as to relieve heat damage to some extent. However, systematic studies on leaf thermal traits are rare.
Methods In the present study, 43 dominant canopy species of four typical vegetation types with varying temperature and precipitation from tropical to temperate zones in Yunnan Province were selected: savanna vegetation, tropical rain forest, subtropical evergreen broadleaf forest, and temperate mixed forest. We selected 23 thermal traits that might have influence on leaf temperature, including leaf morphological, optical, material property, anatomical and physiological traits.
Important findings The results showed that plants in savanna vegetation mainly relied on transpiration for cooling. Savanna species have thin leaves and short life span. They are mainly “quick investment-return” species. Tropical rain forest plants developed large leaves, with low transpiration rates, which have no advantage of leaf cooling. Thick leaves and high water content can alleviate high temperature to some extent. They adopted “slow investment-return” strategy. Subtropical evergreen broadleaf forest was rarely exposed to extreme temperatures. The species had thick leaves, long leaf life span, and adopted “slow investment-return” strategy. They did not show obvious thermal adaptation traits. Temperate mixed forest had small and thick leaves, growing in clusters which provides benefits for thermal insulation. Photosynthetic rate of canopy evergreen plants in this forest was low, adopting “slow investment-return” strategy, while photosynthetic rate of deciduous plants was high, presenting “quick investment-return” characteristics. This study systematically investigated the variation of leaf thermal traits and plant adaptation strategies along temperature and precipitation gradients, providing a theoretical basis for further understanding of plant adaptation to the environment.

Plant-soil feedback (PSF), as an important driving force for plant distribution, community composition, and succession, has received extensive attention in recent years. The spatial-temporal variation are important factors driving PSF; however, there is currently a lack of review on its research progress. We summarized the research progress on the spatial-temporal variation of PSF and proposed research directions that could be pursued in the future. At the temporal scale of PSF, the relationships among plant developmental stages, experimental cycles, and feedback effects were emphasized. At the spatial scale of PSF, we focused on the spatial distribution and transfer of plants, the spatial differentiation of soil microbial communities and physicochemical factors, as well as the influence of above- and below-ground systems on PSF. Based on the research progress, we proposed to focus on the long-term, multi-point dynamic feedback to improve the temporal resolution of the feedback process. The buffering time of microbial communities on domesticated and tested plants needed to be considered, and reasonable domestication and feedback periods should be set to make the results more objective. At the spatial scale, the effects of plant spatial distribution, spatial heterogeneity of soil factors, and above- and below-ground systems on feedback effects should be paid attention. Efforts should be made to achieve similarity in the physical structure of the inoculated soil, in order to obtain more realistic feedback effects.

Aims As pioneer tree species in temperate and boreal forests, birch species (Betula spp.) play an important role in the restoration of secondary forests. Under the current climate change, little is known about the anatomical characteristics of the xylem of different birch species in response to climate change and their adaptation strategies. Therefore, we aim to study the relationship between the characteristics of their xylem vessels and climate, to reveal the response and adaptation strategies of Betula spp. to climate change, and to provide theoretical basis for accurately assessing the impact of climate change on different Betula spp. populations.

Methods In this paper, three natural birch species (B. platyphylla, B. dahurica and B. costata) from Taxus cuspidata National Nature Reserve in Muling, Heilongjiang, China were selected as the research objects. By means of dendrochronology and tree-ring anatomy, we compared these characteristics of xylem vessels of the three birch species, and analyzed the relationship between the characteristics of xylem vessels and seasonal climatic factors, temporal stability, as well as the resistance and recovery of growth to extreme climate.

Important findings (1) The vessel number and vessel density were significantly positively correlated with ring width for all three birch species. The average ring width of B. platyphylla was the widest among the three species, and the vessels were small and numerous. In B. dahurica and B. costata, the average ring width was smaller, and the vessel was significantly larger and less, which made B. dahurica more prone to embolism. (2) The growth of the three species of birch was mainly limited by moisture factors and less limited by temperature. The vessel number of the three birch species was positively correlated with precipitation in each season, and the strongest positive correlation was found in B. costata. The increase of temperature in spring promoted the increase of number of vessels, while the number of birch vessels decreased with the increase of temperature in non-growing seasons. As the climate warmed, B. dahurica tended to have smaller and more vessels, while B. costata tended to have smaller and fewer vessels. (3) The trends of resistance and recovery to drought in the growing season and heat in the non-growing season were similar among the three species, and the resistance and recovery to heat in the non-growing season were lower among the three species. There was great variation among individuals of B. dahurica in response to high temperature in non-growing season. We found that different birch species had different strategies of xylem vessel characteristics to cope with climate warming. B. platyphylla adopted a more conservative strategy (producing more and smaller vessels) to cope with climate change, while B. costata initially adopted a strategy to improve water transport efficiency through large vessels, which may lead to the first decline and even death. B. dahurica’s strategy was between B. platyphylla and B. costata, with moderate number and size of vessels.

Desert annuals develop their special germination time pattern under severe environmental conditions, called germination heterochrony. It refers to the phenomenon that under specific conditions, a portion of the sibling seed population with uniform morphology can germinate instantly, while the other portion remains in the seed bank. Most existing studies on germination heterochrony of desert annuals have focused on seed germination characteristics, post-germination traits, and reproductive allocation. We reviewed and analyzed recent advances in germination heterochrony research, with emphases on 1) conception of germination heterochrony; 2) species and distribution of annual plants with heterochronous germination; 3) effects of heterochronous germination on plant life history types and patterns; 4) differences in phenotypic response, such as survival rate, phenological characteristics, reproductive yield, and biomass allocation, among plants that germinate at different times; 5) biological and environmental factors of germination heterochrony. Based on the review of literature, the future research is expected to contribute to a deeper understanding of germination heterochrony and adaptive mechanisms of desert annuals.

Aims Trees can resorb the nutrients from senescing leaves, which could reduce their dependence on the changing external nutrient availability and improve their adaptability to the environments. Compared with the well addressed macronutrients, however, trace elements have received far less attentions in their resorption efficiency. Therefore, we conducted a field sampling to address the variations in trace element resorption efficiency of the leaves of different tree species with different life forms in a common garden.

Methods In August 2019, we investigated the concentrations of five trace elements (Al, Fe, Mn, Zn, and Cu) in green and senescent leaves of eight tree species in a common garden in mid-subtropical region, and analyzed the resorption efficiency of these elements to explore the nutrient use strategies.

Important findings Evergreen trees (including needleleaf and broadleaf species) exhibited relatively higher resorption efficiencies of Mn, Zn and Cu than deciduous broadleaf trees, although there were insignificant resorption characteristics of Al and Fe regardless of tree species. Higher Mn resorption efficiencies (>30%) were detected in Pinus massoniana and Cinnamomum camphora than in other tree species, while the resorption efficiencies of Mn were insignificant from zero in Castanopsis carlesii, Michelia macclureiand Sapindus saponaria. In contrast, the resorption efficiencies of Zn in Cinnamomum camphoraand Cu in Liriodendron chinensewere 67% and 52% respectively. Liquidambar formosana showed obvious accumulation of Zn and Cu in senescent leaves (-30% and -23%). Moreover, negative correlations were observed between the resorption efficiency of trace elements and the content of corresponding soil elements, and the nutrient resorption efficiency of trace elements displayed synergy relationships with that of major elements. These results strongly suggested that evergreen broadleaf species could develop better nutrient use strategies with more efficient resorption of trace elements than trees of other life forms in this region.

Aims This study aims to clarify the differences in ecological strategies between karst and non-karst forest tree species, in terms of leaf morphology and anatomy, hydraulics, and mechanical resistance.

Methods A total of 101 tree species were selected from typical karst and non-karst forests in tropical-subtropical regions. We measured: (1) leaf morphological and anatomical traits including leaf thickness (LT), leaf density (LD), vein density and leaf mass per area (LMA); (2) leaf mechanical traits including force to punch and force to tear (F_t); and (3) leaf hydraulic traits including maximum hydraulic conductance (K_{leaf_max}), cavitation resistance (P50_leaf), turgor loss point (Ψ_tlp), and stomatal safety margin (HSM_tlp). We compared the differences in leaf traits between karst and non-karst forest tree species, and analyzed their traits correlation networks.

Important findings (1) Compared to non-karst forest tree species, on average the karst tree species had greater F_t, higher K_{leaf_max}, lower (more negative) Ψ_tlp and HSM_tlp. (2) Leaf trait network of karst forest tree species showed shorter average path length and diameter and lower edge density than non-karst forest tree species, indicating that traits combinations were closer in karst forests. (3) Mechanical traits and LMA showed high connectedness in the trait networks of karst forest tree species, LT and LD showed high connectedness in those of non-karst tree species. In karst forest tree species, LMA was positively correlated with F_t and negatively correlated with Ψ_tlp, indicating that increasing leaf carbon investment can simultaneously enhance meachnical resistance and drought tolerance. However, no such correlations were found in non-karst forest tree species. (4) Across karst forests tree species, we found a significant tradeoff between K_{leaf_max} and P50_leaf, both of which were not related with leaf mechanical resistance, and morphological and anatomical traits. By contrast, there was no hydraulic tradeoff in non-karst forest tree species, and K_{leaf_max} was significantly correlated with LT and LD. This study further reveals that compared to non-karst forest tree species, karst forest tree species tend to exhibit isohydraulic strategy and show closer coordination among leaf traits.