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.

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 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.

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.

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.

Soil organic carbon (SOC) is an important carbon (C) pool in terrestrial ecosystems. Pant diversity can enhance SOC content in forests, grasslands, and agricultural ecosystems, and its potential effects on the composition and stability of SOC have aroused increasing interest. However, there is no systematic review of their underlying mechanisms. The present study therefore summarizes advances in research on the effects of plant diversity on the content, composition and stability of SOC and the underlying mechanism with the aim of providing a scientific basis for maximizing soil carbon and nitrogen (N) sequestration and mitigating global climate change through the promotion of plant diversity. Increasing plant diversity can increase the inputs of plant litter biomass into soils, enhance the quality of mixed litter (e.g., lower C:N), and promote the turnover and accumulation of SOC. It can also increase plant-derived C via root and litter inputs to soils, or increase microbe-derived C via enhanced microbial turnover. These processes can also increase soil particulate organic carbon (POC) and mineral associated organic carbon (MAOC) contents. In addition, increasing plant diversity can increase the stability of soil organic carbon by enhancing aggregate protection, changing mineral ion concentrations, and changing microbial community structure. Future studies are needed to investigate (1) how soil organic carbon content may be increased through integrated plant diversity and management options; (2) how the effects of plant diversity on soil organic carbon content and composition can be explored through long-term plant diversity field experiments in different ecosystems; (3) how the effects of plant diversity on soil organic carbon composition and stability can be examined using new experimental methods(e.g., isotope labeling); and (4) how the mechanisms underlying plant diversity effects on soil carbon content, composition and stability can be studied at different soil depths.

Aims The increases in drought intensity and frequency severely threaten structure and functioning of terrestrial ecosystems. To ensure the normal functioning of ecosystems under such scenarios, it is critically needed to understand the spatial-temporal characteristics of ecosystem productivity response and resilience under meteorological droughts.

Methods The intensity and frequency of meteorological droughts were quantified by standardized precipitation evapotranspiration index (SPEI) of the Hai River Basin (HRB). Net primary productivity (NPP) of natural ecosystems was estimated based on Carnegie-Ames-Stanford Approach (CASA). We quantitatively analyzed the relationship between NPP and SPEI, evaluated the drought risk of natural vegetation and the resilience of vegetation after drought.

Important findings (1) Both NPP and normalized differential vegetation index (NDVI) in the HRB showed significantly increasing trend. (2) The lagging time of NPP response to droughts follow an order of grassland and savanna < deciduous broadleaf forest and woody savanna < deciduous-evergreen mixed forest and closed shrubland. (3) Drought risk followed an order of grassland > closed shrubland > woody savanna > deciduous broadleaf forest > savanna > deciduous-evergreen mixed forest. (4) More than 75% of the vegetation in the HRB showed no continuous distinctly low NPP status one month after the droughts, indicating relatively strong resilience. The resilience of forests was stronger than shrub or herbaceous vegetation, which showed opposite temporal pattern within each growing season but shared similar increasing trend interannually. Response and resilience characteristics of NPP varied with vegetation types and drought intensity. Ecosystem stability of the HRB could be improved by adjusting the afforestation and grass restoration measures based on vegetation drought risk and resilience, optimizing vegetation structure, and enhancing species diversity.

Aims Water use efficiency (WUE) is an important indicator for understanding the carbon and water cycles and coupling mechanisms in terrestrial ecosystems. Inherent water use efficiency (IWUE) is a more suitable indicator than WUE for analyzing the carbon-water coupling mechanism of ecosystems on a daily scale. Here, we aimed to investigate the mechanism of water and carbon fluxes and their responses to drought in a planted forest ecosystem.

Methods We carried out an in-situobservation on the water and carbon fluxes and environmental factors in a Quercus variabilisplantation using eddy covariance techniques and the micrometeorological observation system. The effects of biophysical factors on the gross primary productivity (GPP), evapotranspiration (ET), and IWUE during 2021-2022 were analyzed.

Important findings GPP, ET, and IWUE showed obvious seasonal variations. GPP and ET in the wet year were 7.9% and 21.0% higher than those in the normal year, respectively, whereas IWUE in the wet year was 21.4% lower than that in the normal year. Vapor pressure deficit (VPD) was the main factor affecting GPP in the normal year, and net radiation (R_n) was the primarily factor limiting GPP in the wet year. ET was mainly determined by R_n in both normal and wet years. Relative extractable soil water (REW) was the main factor regulating IWUE in the normal year, whereas leaf area index (LAI) was the main factor controlling IWUE in the wet year. Environmental factors regulated carbon and water fluxes by affecting canopy conductance, and consequently impacting IWUE. The occurrence of soil drought significantly increased IWUE. The response of GPP and ET to REW showed a time lag of 1 month, while the response of IWUE to REW had no lag.

Soil microorganisms are key drivers of carbon (C) cycling in terrestrial ecosystems not only by facilitating soil organic C decomposition and CO₂ emission, but sequestering atmospheric CO₂ into soil organic C through microbial C fixation. Due to the ubiquitous presence of microorganisms in soils, microbial C fixation is vital for terrestrial ecosystem C cycle globally. In this paper, we explored the mechanisms and determinants of soil microbial C fixation based on data collections and analyses to address the following the three issues: 1) the pathways and processes of autotrophic microbial C fixation in soil; 2) the pathways and processes of heterotrophic microbial C fixation in soil; and 3) the impacts of soil properties, ecosystem types, and climate change (i.e., warming and precipitation change) on microbial C fixation. Overall, the paper provides insights into the dynamics of C fixation in terrestrial ecosystems which is helpful for better understanding the uncertainty of soil C pool in the relationship to microbial C fixation, and which also lays a theoretical foundation for advancing of C cycling models under climate change.

Aims This study primarily aims to investigate the spatiotemporal evolution patterns of fractional vegetation cover (FVC) in the grasslands of Xinjiang section of Tianshan Mountains over the period 2001 to 2020. It seeks to elucidate the determinants of these patterns, emphasizing the influence of vegetation types, livestock farming practices, precipitation levels, and mean annual air temperature. Ultimately, the goal is to contribute important insights that will inform decisions concerning the sustainable management and ecological conservation of these grasslands.

Methods The investigation into the spatiotemporal evolution patterns of vegetation in Xinjiang section of Tianshan Mountains and the factors influencing these patterns leveraged MODIS NDVI remote sensing data spanning two decades. A suite of analytical techniques, including Senʼs Slope Estimator + Mann-Kendall trend analysis, coefficients of variation, and land-use dynamics assessments, were employed to analyze the spatiotemporal variations in grassland FVC.

Important findings The study revealed a general stability in FVC, with the multi-year average varying between 0.33 and 0.42. Notable FVC increases were observed in the northeastern and southwestern low-altitude areas of the range, comprising 3.14% of the analysis area. In contrast, significant FVC declines were predominantly in the Ili River Basin, representing 15.81% of the area studied. The dynamics of grassland FVC were primarily driven by vegetation types and the total value of livestock farming output, each influencing over 29.85% of the variation. When considering the interaction with precipitation and mean annual air temperature, the influence of these factors on FVC increased to above 48.70%. Furthermore, a positive association between FVC and both annual precipitation and average annual temperature was noted, with areas displaying a correlation to precipitation covering 80.84% of the total area, largely encircling the basins flanking Tianshan Mountains range. Meanwhile, a correlation with mean annual air temperature spanned 71.69% of the area, predominantly at higher elevations. These findings offer valuable reference data to support strategic planning for the sustainable use and protection of grassland ecosystems in the Tianshan Mountainous region.

Aims Functional traits can individually or jointly reflect the response of plants to environmental changes and their adaptation strategies and are closely linked to ecosystem functioning. Exploring the functional traits and trait space characteristics of wetland plants is of importance for understanding the mechanisms underlying the ecological adaptability of wetland plants in river floodplains.

Methods We measured 10 functional traits of 30 common herbaceous plants in 5 river floodplains around Wuhan in middle reaches of Yangtze River. We then analyzed the relationships among traits, the quality of trait space, the importance of traits, and the distribution of species in trait space.

Important findings The results showed that variations in functional traits were large among wetland plant species and that trait-trait relationships were generally weak. The quality of trait space increased rapidly when the dimension of space increased from one to four, with the six-dimensional space being of the highest quality. Considering a tradeoff between dimension reduction and space quality, we chose the four-dimensional space for subsequent analyses. In the four-dimensional space, life span, rhizome, plant height, leaf area, specific leaf area, leaf dry matter content, leaf nitrogen content and leaf carbon content were significantly correlated with the axes of the trait space, indicating that they played an important role in shaping the trait space of wetland plants. Sixteen species were located at the vertices of the convex hull, of which ten had high frequencies of occurrence, indicating that these species hold unique trait values and might be more important in shaping the trait space than other species.

Coarse woody debris (CWD) consists mainly of log, snag, large branch, stump and coarse root. CWD is widely distributed on the forest floor and especially valuable in most of forest ecosystems because it is vital to the global carbon cycling and biodiversity conservation. In particular, increasingly extreme climatic events, such as persistent high temperature, prolonged drought, and tropical cyclones are greatly affecting forest ecosystem function and stability by accelerating tree death, changing the sources of CWD inputs and decomposition processes. Thus, research about CWD decomposition has becoming an ecological hotspot. More and more ecologists have contributed greatly in disentangling the mechanisms on how factors control decomposition process and how CWD nurses biodiversity, which have greatly stimulated the development of CWD ecology. In this review, firstly, we summarized the dominant methodology used in the CWD decomposition study. Then we introduced the scenarios which could be applied for each method. Secondly, we described the morphological, physical and chemical properties of CWD during decomposition, respectively. Thirdly, we overviewed previous studies disentangling factors affecting decomposition dynamics. Briefly, substrate quality, decomposer community and environmental conditions are the main control factors of CWD decomposition. Substrate quality and decomposer community dominate the CWD decomposition process at site scale, with substrate quality regulating the decomposer community with bottom-up effects, while environmental conditions functioning at regional or broad scales. Fourthly, huge amount and diverse types of organisms use decaying CWD as a habitat, many of which are endangered species. It is fundamental to maintain the biodiversity in the CWD ecosystem. Epixylic plants (especially for bryophytes), bacteria, fungi and invertebrates are the common species living on/in the CWD. Invertebrates can utilize CWD in different ways, such as habitat, nourishment and foraging sites, which are species specific. The community composition changed along with decomposition process. The succession of epixylic plants is correlated with the duration of decomposition, while the succession of other types of organisms is mainly driven by the changing substrate quality of decaying CWD. Additionally, we summarized the decomposition dynamics of different structural components (bark vs. xylem) and the interaction between bark and xylem during CWD decomposition which have been overlooked. Finally, as the long decomposition time and the limitation of methodology impeded the progress of revealing the mechanism of CWD decomposition, we made an outlook of future research in the area of decomposition mechanism and biodiversity conservation, and provided methodology that could be of help in stimulating the further development in CWD ecology.

TThe Juniperus przewalskii forests are a unique forest community in China, widely distributed in the mountains on the northeastern edge of the Qinghai-Tibet Plateau. They play crucial roles in slope protection, soil conservation, water source preservation, and habitat improvement. A systematic study of their distribution, composition, and characteristics can provide a scientific basis for the healthy development and artificial management of Juniperus przewalskii forests, enabling them to better fulfill their ecological role in cold and arid areas. This study conducted a comprehensive survey of Juniperus przewalskii forests throughout the plant growth season from 2018 to 2022. A total of 52 survey sites were selected and 72 survey plots were established, covering the entire distribution area of Juniperus przewalskii forests. The 72 survey plots were analyzed using community ecological analysis methods such as cluster analysis and quantitative statistics. The main findings are as follows: Juniperus przewalskii forests are primarily distributed on sunny and semi-sunny mountain slopes at altitudes of 2800 to 3800 meters, usually inhabit dry, barren, and steep slopes, where the habitat conditions are relatively harsh. The existing forests are mostly climax communities of secondary successional, The forest stands are relatively sparse, with a canopy density of 0.2 to 0.6 and an average height ranging from 5 to 13 meters. The vertical structure consists of tree layer, shrubby layer, and herbaceous layer. The tree layer is dominated by Juniperus przewalskii, and the diameter class structure shows a right-skewed normal distribution, with the diameter at breast height mainly concentrated between 4 to 8 centimeters. The composition of the shrubby and herbaceous layers vary significantly depending on the specific habitat conditions. A total of 370 species of vascular plants have been recorded, distributed among 48 families and 151 genera. Among these, angiosperms comprise 45 families and 148 genera, gymnosperms consist of 2 families and 2 genera, and ferns are represented by 1 family and 1 genus. The top three dominant families are Asteraceae, Poaceae, and Fabaceae. In the composition of life types, there are obviously more herbaceous species than woody species. Based on the dominant and characteristic species of the community, Juniperus przewalskii forests can be further classified into 11 association groups and 25 associations. The spatial distribution exhibits a clear ecological sequence, arranged by altitude from low to high, the sequence includes the Juniperus przewalskii-Berberis diaphana-Herb Association Group, Juniperus przewalskii-Dasiphora fruticosa-Herb Association Group, Juniperus przewalskii-Dasiphora parvifolia-Herb Association Group, Juniperus przewalskii-Dasiphora glabra-Herb Association Group. In areas subjected to significant human disturbance, the community transitions into the Juniperus przewalskii-Herb Association Group.

Aims Exploring the characteristics of carbon source-sink has significant implications for guiding local governments in achieving its “dual carbon” goal. This study comprehensively assessed the dynamics of carbon emissions, terrestrial carbon sinks, the contribution of terrestrial carbon sinks in offsetting carbon emissions, and the impacts of clean energy production on the carbon emissions in Yunnan Province from 1981 to 2020, and further investigated the terrestrial carbon balance in the next four decades projected by coupled model intercomparison project phase 5 (CMIP5) earth system models under two climate scenarios.

Methods Two independent methods were used to estimate historical ecosystem carbon sinks in Yunnan Province. One was based on field observation data combined with empirical models, and the other was based on four terrestrial ecosystem models. The projections of future carbon balance in Yunnan Province were derived from five earth system models of CMIP5 under two scenarios (RCP4.5 and RCP8.5). Carbon emissions were estimated using the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories, and China’s Provincial Guidelines for Greenhouse Gas Emission Inventory.

Important findings The results show that the terrestrial carbon sink in Yunnan Province varied between 12.41 and 31.22 Tg C·a^-1 over the past 40 years, with an average sink of 19.41 Tg C·a^-1. The highest ratio (247%) of ecosystem carbon sinks to carbon emissions (sink emission ratio) in Yunnan Province occurred during the period from 1981 to 1985, while the ratio has declined since then and reached its lowest value during the period of 2006-2010 followed by a slight increase after that. The ratio was 54% during the period of 2016-2020. The rise of the sink emission ratio in the past decade can be mainly attributed to the promotion of clean energy production, the increase in forest area, and the decrease in energy intensity. Large-scale deployment of clean energy in Yunnan Province has in general satisfied the energy needs of economic development, reducing the reliance of its economy on CO₂ emissions. Model projections indicated that under future climate change scenarios (RCP4.5 and RCP8.5), the net ecosystem productivity (NEP) in Yunnan Province during the 2020s and the 2030s may be lower than that during 2016-2020, while carbon sink may increase in the 2040s to 2050s. This study suggests that in the future, Yunnan Province should further develop clean energy programs, increase energy efficiency, and enhance ecosystem carbon sink to support both the achievement of carbon neutrality and regional high-quality development.

Aims Arbuscular mycorrhizal fungi (AMF) are widely distributed in grassland ecosystems. They make great contribution to the productivity and stability of grassland ecosystems. Our purpose was to explore the AMF community distribution characteristics and driving mechanism in grassland ecosystems.

Methods This study was conducted in 18 different grassland types. We demonstrate the AMF community characteristics and driving factors by investigating plant community characteristics, analyzing soil physicochemical properties and AMF communities.

Important findings In different grassland types, the dominant genera of AMF community were Claroideoglomus, Septoglomus, Diversispora, Rhizophagus, Acaulospora, Glomus and Ambispora. In addition, there exist significant differences in speicies composition and diversity of AMF communities, and the AMF diversity and rare operational taxonomic unites (OTUs) in Stipa purpurea grassland was relatively higher than those of other grassland types. Results from the structural equation model showed that AMF community diversity was significantly influenced by plant community diversity and soil pH, and AMF community composition was significantly influenced by temperature, soil moisture content and plant community composition. To sum up, abundant AMF resources were contained within Chinese natural grassland, and the AMF community characteristics in different grassland types are significantly different. Meanwhile, plant communities have remarkable driving effect on AMF communities in grassland ecosystems. So protecting grassland plant diversity is of great importance for maintaining soil microbial community stability.

Aims Our study aims to explore water usage strategies and the competitive or complementary relationships among neighboring arboreal and shrubby plants within the same stand under diverse rainfall conditions. Through an analysis of soil water absorption and water niche characteristics of these neighboring plants, we aim to provide a theoretical basis for vegetation restoration and management in the rocky mountainous areas, Beijing.

Methods Xylem samples were collected from trees including Robinia pseudoacacia, Koelreuteria paniculata, and Platycladus orientalis, as well as from the shrub Vitex negundo. Additionally, samples of soil, groundwater, and rainwater were gathered both before and 1-4 days following different types of rainfall events: light rain during a dry period, moderate rain during a wet period, and rainstorms during a dry period. These samples were analyzed to examine the characteristics and dynamic changes of hydrogen and oxygen isotopes composition (δ²H and δ¹⁸O). The MixSIAR model was employed to determine the contribution rates of groundwater and soil water from different soil layers to various plant species. Furthermore, water niche width and niche overlap were assessed using the Levins index and Levins overlap formula, respectively.

Important findings The results indicate that soil water content, δ²H and δ¹⁸O, water absorption depth, and niche characteristics of neighboring arboreal and shrubby plants were significantly influenced by the types of rainfall. Following light rainfall during a dry period, shrubs exhibited heightened sensitivity to precipitation, shifting their water source from deep soil to upper soil layers, while arboreal species predominantly relied on groundwater. After moderate rainfall during a wet period, arboreal and shrubby plants from different forest types primarily absorbed water from soil layers within the 0-40 cm depth range. Rainstorms during a dry period altered the water utilization strategies of arboreal and shrubby plants, with shrubs predominantly sourcing water from the 0-40 cm soil layers, while arboreal species exhibited more uniform water uptake across different soil layers. The niche width of R. pseudoacacia and K. paniculata was lower compared to corresponding shrubs before and after light rainfall during a dry period, whereas the niche width of K. paniculata exceeded that of understory shrubs both before and after rainstorms during dry periods. Platycladus orientalis and understory shrubs exhibited similar responses to different types of rainfall, with the niche width of P. orientalisexperiencing a sharp increase on the first day following rain, while that of shrubs spiked on the second day post-rainfall. For the dry period before light rainfall, there was a substantial overlap in the water niche between R. pseudoacaciaand understory shrubs, which diminished with an increase in the number of rainfall days thereafter. Except for the dry period before light rainfall, arboreal and shrubby plants demonstrated distinct water utilization strategies across different types of rainfall, thus mitigating water competition between them.

Aims The response of herbaceous and woody plants to environmental stress is an important mechanism for the evolution of ecosystem structure and function in hydro-fluctuation belt of Three Gorges Reservoir. However, the pertinent response characteristics and whether there are group differences in these stress responses are still unclear.

Methods Here, we undertook a meta-analysis of the effects of typical environmental stresses (flooding and drought stress) on the physiological and ecological characteristics of suitable herbaceous and woody plants in the Three Gorges hydro-fluctuation belt, with an aim to reveal the response of suitable plant groups to flooding and drought stress from the perspective of species and life forms.

Important findings The results showed that: (1) Herbaceous plants and woody plants showed obvious growth and development inhibition and adaptive response in physiological and biochemical strategies under environmental stress, mainly manifested in the decrease of biomass and photosynthetic rate of each tissue and organ, the increase of malondialdehyde and proline content, and the initiation of antioxidant enzyme system (superoxide dismutase, peroxidase, catalase). (2) Flooding stress had the strongest negative effect on herbaceous plant biomass, followed by drought stress. Flooding stress had the greatest negative effect on total chlorophyll content and photosynthetic rate of woody plants, followed by drought stress, showing the life-form effect of environmental stress. However, the total chlorophyll content of herbaceous and woody plants was most sensitive to flooding stress, while woody plants showed a certain homeostasis to drought stress. The physiological and biochemical responses of woody plants to flooding stress were more significant than those of herbaceous plants, and the responses were mainly different from those of herbaceous plants in stomatal conductance, malondialdehyde and proline content, and peroxidase activity. The herbaceous plants showed stronger response to drought stress than did woody plants, and the response of total chlorophyll content, water use efficiency and antioxidant enzyme (superoxide dismutase, peroxidase, catalase) activity was different from that of woody plants. (3) The morphological responses of herbaceous and woody plants to different environmental stresses have tissue-specific differences. Herbaceous plants mainly adapt to flooding and drought stress by morphological changes of roots, stems and leaves, while woody plants mainly adapt via morphological changes of roots. In summary, this study presents an integrated view of the morphological and physiological characteristics of herbaceous and woody plants in response to environmental stress in the hydro-fluctuation belt of the Three Gorges Reservoir, which provided a scientific basis for evaluating the potential of different life-form vegetation in the ecological structure and functional restoration in this ecologically-important region.

Aims Schoenoplectiella triangulata is an emergent plant species widely used in wetland vegetation restoration. It is important to study the germination and dormancy characteristics of S. triangulata seeds from different populations for germplasm collection and scientific utilization.

Methods In this study, differences in the morphological characteristics and germination characteristics of S. triangulata seeds were investigated, and the mechanisms of seed dormancy were explored.

Important findings (1) The seeds of S. triangulata showed physiological dormancy (PD), and there were significant differences in morphology, PD, 1 000-grain mass and water absorption characteristics among populations. (2) Light and variable temperature were conducive to seed germination of S. triangulata.(3) Sand storage at low temperatures, water storage at low temperatures and sand storage at normal temperatures helped to break the dormancy of S. triangulata seeds. Both fluridone and gibberellin treatments also helped to break the dormancy of S. triangulata seeds, but these effects varied among different populations. (4) Among different populations of S. triangulata, seed morphological characteristics, germination characteristics and dormancy characteristics were correlated with environmental conditions of the collection site. These results indicate that provenance should be considered when S. triangulata seeds were applied in wetland ecological restoration and that proper seed treatments before sowing could improve seed germination and the effectiveness of ecological restoration.

Aims The ecological stoichiometric characteristics and variation of plant leaves can reflect the response of plants to their environment, serving as a key to understanding the interaction between plants and the environment. The unique Tiankeng environment creates favorable conditions for plant growth. By exploring the nutrient utilization characteristics and environmental adaptability differences of Tiankeng plants, this study aims to reveal the adaptive mechanism of Tiankeng forest plants, and basic data can be provided for nutrient cycling and community construction in Tiankeng forest.
Methods Our study compared the chemical stoichiometry of carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) nutrients in the leaves of plants inside and outside the Tiankeng Complex in Dashiwei, Guangxi. Statistical methods such as correlation analysis and redundancy analysis were used to explore the intrinsic relationship between chemical stoichiometry and the influence of environment on these characteristics.
Important findings (1) The leaves of 64 plant species from 36 families and 55 genera in the study area have lower C content, higher N, P, K, Ca, Mg contents, and lower C:N, C:P compared to plants in other karst and terrestrial plants in China. This indicates that the plants in Tiankeng Complex are characterized by low C sequestration, high nutrient accumulation, high growth rate, and low nutrient utilization efficiency. (2) The N:P mean value of the plant leaves in the Dashiwei Tiankeng Complex was 16.65, the N:K mean value was 1.50, and the K:P mean value was 10.10, indicating that the Tiankeng plants generally have an abundance of K content but are limited by N and P contents. (3) There were significant differences in the nutrient content and stoichiometric ratios of plants in different locations and functional groups. Different environments and plant types adopt distinct nutrient absorption strategies. (4) Correlation analysis showed that there were significant correlations between most of the nutrient contents and stoichiometric ratios of plant leaves, indicating that the nutrient uptake by plant leaves had a certain proportional composition and coordinated relationship. (5) Redundancy analysis showed that soil is a key environmental factor influencing leaf nutrients. The results of our study revealed the characteristics of plant nutrient utilization, habitat nutrient differences, and plant adaptability to the environment in the Dashiwei Tiankeng Complex, providing basic data for exploring the nutrient cycling and community construction mechanism of Tiankeng forest ecosystems.

Aims Climate warming exacerbate vulnerability of forest ecosystem in the Qinling Mountains, leading to increased forest mortality, and declined ecological function. The objectives of this study were to investigate xylem embolism vulnerability and hydraulic safety margin of nine tree species in the Qinling Mountains.

Methods In this study, nine tree species of the Qinling Mountains, Betula albosinensis, Corylus ferox, Acer davidii, Acer maximowiczii, Quercus acutissima, Quercus aliena, Pinus armandii, Picea asperata and Larix principis-rupprechtii in two different forest sites, Xunyangba village in mid altitude and Pingheliang ridge in high altitude, were studied. Cochard centrifugation and Sperry centrifugation methods were used to establish vulnerability curves (VCs), which was defined as the percentage loss of hydraulic conductivity (PLC) vs. xylem water potential. The xylem maximum hydraulic conductivity (K_max) of branches was measured by low pressure flowmeter. The midday xylem water potential (P_md) was determined by the pressure chamber, which was used to obtain the hydraulic safety margin (HSM) to assess the risk of hydraulic failure for each tree species in natural conditions.

Important findings 1) Xylem embolism vulnerability of nine species was ranked as Picea asperata < Larix principis-rupprechtii < Pinus armandii < Acer davidii < Acer maximowiczii < Betula albosinensis < Quercus aliena < Corylus ferox < Quercus acutissima. The HSM was ranked as Picea asperata > Pinus armandii > Acer davidii > Acer maximowiczii > Quercus aliena > Larix principis-rupprechtii > Betula albosinensis > Corylus ferox > Quercus acutissima. 2) The six broadleaf species in the Qinling Mountains had less negative 50% PLC water potential (P₅₀) and narrower HSM in average than the three conifer species, and therefore were under greater risk of hydraulic failure. 3) The HSM of B. albosinensis, C. ferox and Q. acutissima were close to 0, which indicated an extremely high risk of xylem embolism. In conclusion, broadleaf species in Qinling Mountains had higher water transport efficiency than conifer species, in the cost of higher risk of xylem embolism and hydraulic failure.

Aims Non-structural carbohydrates (NSCs) include starch and soluble sugars, the transformation of which enhances plant resistance to environmental stresses. Tropical rainforests play an important role in the carbon (C) pool of terrestrial ecosystems and in mitigating climate change, and they are also hotspots for atmospheric nitrogen (N) and phosphorus (P) deposition. To date, the response of leaf NSCs of dominant plants in primary and secondary forests to long-term N and P inputs is unclear.

Methods We investigated the effects of long-term N and P inputs on leaf NSCs of eight species from each of the primary and secondary forests based on a 10-year N and P addition experiment in Jianfengling, Hainan, and analyzed the relationships of NSCs with each of the leaf traits, photosynthesis parameters, and soil nutrients.

Important findings Dominant plant leaves in the secondary forest had higher soluble sugar and NSCs contents than that in the primary forest. Low N addition significantly reduced the content of starch, P addition significantly increased the content of soluble sugar, and combined N and P additions enhanced the ratio of soluble sugar and starch in dominant plant leaves of primary forest; whereas N and P additions did not impact the NSCs content of dominant plant leaves of secondary forest. In the two forests, leaf NSCs content of eight species were negatively correlated with leaf pH and specific leaf area, while positively correlated with leaf C content, photosynthesis rate, and photosynthetic N use efficiency. There was significant positive relationship between leaf NSCs and each of soil available N, total P contents in secondary forest. These results suggest that leaf NSCs of dominant plants is jointly impacted by leaf traits and soil nutrients in tropical rainforests. From the perspective of the leaf C economy, our study demonstrates that dominant plants are more sensitive to atmospheric N and P deposition in primary than in secondary forests, thereby highlighting the importance of protecting tropical primary rainforests.

Aims Differences in herbivory among plant species can greatly affect the functioning of forest ecosystems. However, little is known about the main drivers causing interspecific differences in herbivore damage among tree species. The growth-defence trade-off hypothesis posits that the intrinsic growth rate of plant species governs resource allocation between defense and growth, thereby shaping interspecific variation in herbivory. However, the validity of this hypothesis is extensively debated, especially in highly species-rich subtropical forests.

Methods We quantified leaf herbivore damage in 27 native tree species in a tree species diversity experiment conducted in subtropical China. We measured 12 leaf traits associated with insect palatability and relative growth rates of 27 tree species. Using a combination of phylogenetic multivariate analyses, we assessed trade-offs between leaf traits and the relative effect of these traits on leaf herbivore damage.

Important findings We found 1) neither phylogenetic principal component analysis nor hierarchical cluster analysis supported the idea that species displayed one-dimensional trade-off; 2) Conventional strategies, such as content of condensed tannins, are not strongly involved as a defence against herbivores; 3) No significant trade-off between plant intrinsic growth rate and chemical defence traits for the 27 studied tree species. Our results do not support arguments for growth-defense trade-off hypothesis. Rather, plants exhibit a range of combinations of leaf traits. We suggest this lack of a one-dimensional trade-off may be adaptive, resulting from selective pressure to adopt a different combination of defences to coexisting species.

Aims With global climate change, the increased frequency and intensity of droughts lead to forest degradation, slow down tree growth, and even cause the death of trees. It is critical to understand the mechanisms of how drought influences tree radial growth, and to quantify the effect of drought intensity on tree radial growth.

Methods This study used correlation analysis to determine the main limiting climatic factors for radial growth of Picea crassifolia at three altitudes in the western Qilian Mountains, and then compared the response of tree radial growth to drought events with different levels of intensity, with respect to resistance, recovery, resilience, and growth deviation.

Important findings Tree radial growth across three altitudes was most responsive to the mean temperature of June, precipitation, and standardized precipitation evapotranspiration index (SPEI), with SPEI being more pronounced, indicating that tree radial growth is strongly limited by drought stress. Radial growth of trees at three altitudes varied significantly with dryness and wetness. In response to increased drought intensity, tree resistance decreased and recovery increased. Trees at three altitudes exhibited compensatory growth after moderate and extreme drought events, but this compensatory growth was transitory, with growth condition returning to the pre-drought level in the second year. Following the severe drought events, trees at three altitudes did not exhibit compensatory growth in the first year. These results suggest that growth dynamics in the first year after a severe drought event is critical for predicting the growth recovery of P. crassifolia.

Aims Despite grazing being a significant driving factor for grassland ecosystems, it remains uncertain whether the responses of grassland plant communities and functional groups to soil variables remain consistent across grazing intensity gradients.

Methods This study conducted field plant community surveys in the middle part of the northern slope of Tianshan Mountains, and lab soil analysis. It aimed to analyze the impact of grazing on plant communities and functional groups, as well as reveal differences in their responses to soil factors under grazing intensity.

Important findings The results indicated that perennial grasses and sedges were the main dominant functional groups in light grazing and no grazing sites. However, heavy grazing sites had poisonous grasses as dominant functional groups, with Achnatherum inebrians being the dominant species. Light grazing significantly increased above-ground biomass for functional groups such as perennial grasses, legumes, sedges, and forbs while notably decreased for poison grasses compared to heavy grazing along the gradient. In terms of functional group diversity, Shannon-Wiener index, Margalef index, and Pielou index were significantly higher under light grazing than heavy grazing; however, Simpson index did not show significant differences between different levels of grazing intensity. Results from redundancy analysis, Mantel test, and structural equation models demonstrated significant correlations between plant community characteristics (including functional groups), community diversity indices (Shannon-Wiener index), and various soil factors such as organic carbon content, available nitrogen content, available potassium content, total phosphorus content, total potassium content, soil density, soil water content. Grazing directly exerted a significant negative impact on grassland height, coverage, density, aboveground biomass, diversity within both plant communities and functional groups. The soil density increase and soil nutrient reduction caused by grazing can also impact community height, coverage, density, above-ground biomass, as well as the diversity of plant community and functional groups. In summary, soil factors played a pivotal role in maintaining the stable growth of grassland plant communities amidst grazing disturbance in middle part of northern slope of Tianshan Mountains. The findings provide a scientific foundation for the rational utilization of grassland plant resources in Xinjiang.

Alien plant invasions pose a significant threat to global ecological security. Various factors, including the ecological tolerance of alien plants and their interactions with biotic and abiotic elements such as rainfall, temperature, and soil nutrients, influence the dynamics of plant invasions. The interaction between plants and various micro-organisms plays an important role in regulating plant growth, development, and interspecific competition. Previous studies indicate that the interactions between native plants and different groups of soil microorganisms affect plant invasion through several pathways: 1) Pathogenic microorganisms may have more suppressive effects on native plants, facilitating the invasion of alien plants. 2) Symbiotic microorganisms can help native plants resist alien plant invasion, but disrupting these mutualistic associations may accelerate invasion. 3) Additionally, saprophytic microbiota may promote plant invasions by increasing the rate of nutrient cycling and facilitating these alien plants with high nutrient utilization efficiency. Compared to single-species invasions, multispecies invasions can increase invasive capacity through shared pathogen pressures, forming symbioses, and utilizing heterogeneous nutrients from saprophytic microorganisms. This interspecific synergistic effect can disrupt the balance between native plants and soil microbes. Furthermore, global changes may promote alien plant invasions through the detrimental effects of soil microbes on native plants. This review examines the impact of interactions between native plants and soil microbes on plant invasions and outlines directions for future research.

Aims The reconstruction of regional disturbance history provides important information in understanding the health status of local forests and facilitating their management and protection. However, the history and regimes of disturbances in the Qilian Mountains remain poorly reported.

Methods In this study, we explored the disturbance history of Juniperus przewalskii, a dominant tree species on the sunny slope of the Qilian Mountains. Tree-ring cores were collected and the standard chronologies of tree-ring width from eight sites were established. We analyzed the correlation between climate factors and tree-ring index. By calculating the percentage growth change in each tree, we examined whether there had been tree-growth release or suppression, thereby identifying the historical course and spatial pattern of disturbances.

Important findings Winter air temperature and summer moisture conditions significantly affected the growth of the tree species. The reconstruction of disturbance history highlighted two major forest disturbance events that occurred during the 1930s and 1970s in our study area. These events were intimately linked to extreme cold winters and severe summer droughts, coinciding remarkably with the occurrence of El Niño. Both events showed spatial variability in disturbance, reflecting differences in resistance across forests. Our study results offer new perspectives in mitigating forest degradation and enhancing forest management in the future.

Aims Soil ecological stoichiometry is an important indicator of soil fertility and plant nutrient status. Investigating impacts of restoration approaches on forest soil ecological stoichiometry characteristics provides a theoretical foundation and data support for accurately assessing responses of the ecosystem material cycling processes to disturbance and restoration efforts.
Methods This study compared the forest soil stoichiometry from two forest restoration approaches, i.e., artificial (RG) and natural regenerations (TR) that included three coniferous or broadleaf mixed stands and four deciduous broadleaf stands, respectively, in eastern Northeast China. The carbon (C), nitrogen (N), and phosphorus (P) contents of both soil by horizons, litterfall and litter were determined, as well as the soil properties such as pH and bulk density.
Important findings The results showed that soil C, N, and P contents decreased with the soil depth in the RG and TR. The soil C, N and P contents of the O (organic) horizon varied from 53.78 to 90.59 g·kg^-1, 5.02 to 7.83 g·kg^-1, and 0.75 to 0.91 g·kg^-1 in all the stands, respectively. The soil C and N contents of the RG were significantly lower than those of the TR in the O horizon, while the soil C, N and P contents of the RG were higher than those of the TR in the A (humus) and B (illuvial) horizons. The soil C density of the O horizon in the RG was significantly lower than that in the TR. The C:N, C:P, and N:P varied from 10.08 to 12.53, 43.97 to 135.52, and 4.56 to 11.64 in all the stands, respectively. The C:N of the O horizon had no significant difference between RG and TR, but the C:P and N:P of the O and A horizons in the RG were significantly lower than those in the TR. There was a significant positive correlation between C and N contents in all soil horizons (R² ranged from 0.40 to 0.76). Except for C:N, restoration approaches, soil horizons and their interaction had significant effects on the content, density and stoichiometry of C, N and P in soil. Soil bulk density and litterfall C content significantly affected soil C, N and P contents. These findings suggest that increasing the proportion of coniferous species by reforestation reduced the content of C and N in the topsoil, which decreased the carbon sequestration accordingly. However, restoration approaches had no significant effect on the C:N, featuring a relatively stable carbon and nitrogen stoichiometry.

Aims The trait-based approach has been extensively utilized to evaluate the influence of neighborhood competition on seedling survival. However, previous studies used species average traits, ignoring intraspecific trait variation.

Methods Based on the monitoring of 150 seedling plots in a needleleaf and broadleaf mixed forest in Jiaohe, Jilin, we used a generalized linear mixed effect model of binomial distribution to compare the effects of intraspecific trait variation and species average traits on seedling survival rate, and explore how functional traits mediate seedling responses to neighborhood competition and abiotic environmental factors.

Important findings The intraspecific trait variation model and the species average trait model had inconsistent predictive abilities for seedling survival rate. Specifically, intraspecific variability model of specific leaf area (SLA) exhibited a smaller Akaike information criterion value and Bayesian information criterion value, a larger explanatory variance and a better fit. While species average trait model of leaf area (LA), leaf carbon content (LCC), and leaf nitrogen content (LNC) performed better. In addition, traits mediate the effects of neighborhood competition and soil nutrients on seedling survival. Seedlings with smaller LA have higher survival rates under the same density dependence. Higher LCC increases seedling survival rate in the absence of soil nutrients, while seedling survival rate decreases under fertile soil conditions. The ability of intraspecific trait variation in predicting individual survival of seedlings may not be stronger than species average trait, which may be related to forest stands and environmental factors. In addition, the presence of neighborhood competition and environmental variables can enhance the relationships between traits and seedling survival. Although intraspecific trait variation may not improve the prediction of seedling survival rate, this individual-based approach provides a new perspective for predicting seedling dynamics.

Aims Rhizosphere microorganisms play an important role in plant nutrient acquisition and carbon and nitrogen cycling, and plant fine roots (including absorptive roots and transport roots) are closely related to rhizosphere microbial communities. Elucidating the relationship between changes in fine root traits of pioneer tree species and rhizosphere microbial communities during post-fire forest restoration can provide theoretical support for post-fire vegetation restoration management based on fine roots and rhizosphere microbial dynamics.
Methods The pioneer tree species Betula platyphylla was used as the research object in the 30-year time series of the burned area of Da Hinggan Mountains. The 16S rRNA high-throughput sequencing technology was used to analyze the relationship between rhizosphere bacterial community structure and soil properties and fine root traits of B. platyphylla during post-fire recovery.
Important findings The results showed that post-fire recovery time significantly affected soil pH, absorptive root traits, and rhizosphere bacterial α diversity. With increasing time after fire, soil pH tended to increase, then decrease, and then increase again. The specific root length and specific root area of absorptive roots showed a trend of first increasing and then decreasing. Nine years after the fire was the turning point when the rhizosphere bacterial α diversity of B. platyphylla gradually recovered. Proteobacteria, Actinobacteriota, and Acidobacteriota were the main dominant phyla in the rhizosphere bacterial community at different post-fire recovery times, and Bradyrhizobium was the main dominant genus. Dominant genera such as Roseiarcus, Acidipila and Mycobacterium were significantly different at different post-fire recovery times. The α diversity of rhizosphere bacteria was mainly affected by soil pH and specific root length of absorptive roots, and the change of bacterial community structure was affected by carbon and nitrogen contents of fine roots and phosphorus content of transport roots. In conclusion, the interaction between fine roots, soil, and microorganisms jointly affects the community structure and diversity of B. platyphylla rhizosphere bacteria, thereby shaping the rhizosphere environment and promoting ecosystem recovery after fire.

Aims China harbors extensive grassland resources, yet nearly 70% of these grasslands are afflicted by varying degrees of degradation under the combined pressure of climate change and human activities. Pinpointing the pivotal factors driving grassland degradation and establishing a rapid diagnostic system is imperative for precise condition assessments.

Methods This study was conducted in the Hulun Buir meadow steppe of Nei Mongol. The selected sites were categorized into four degradation levels: non-degraded, lightly degraded, moderately degraded, and heavily degraded. Vegetation and soil indicators were collected. Leveraging the random forests algorithm, degradation indicators were screened and weighted, with efforts made to reconcile ecosystem service priorities between the government and pastoralists.

Important findings This study identified ten key factors characterizing degradation, including aboveground biomass, proportion of high-quality forage, community height, litter biomass, species richness, leaf dry matter content, leaf thickness, soil density, soil water content and soil inorganic water content. These indicators encapsulate diverse ecosystem services, including forage supply, erosion control, biodiversity conservation, vegetation resilience, and water and nutrient regulation. Using non-degraded sites as a benchmark, a degradation index (DI) for the meadow steppes of Nei Mongol was developed, accompanied by delineated DI thresholds for different degradation levels. This study provides foundational data to support judicious selection of indicators for both national and regional standards.

Aims To explore the water age of dominant vegetation at different altitudes in Lushan area in the humid climate region and the strategy of water utilization for different aged sources, so as to provide scientific basis for ecological protection and resource utilization in this region.

Methods Four species of Pinus (P. massoniana at low altitude, P. taiwanensisat high altitude) and Quercus (Q. variabilisat low altitude, Q. serrataat high altitude) from Lushan Mountain were studied, using stable hydrogen and oxygen isotopes technology and linear mixing water age model in order to analyze the transpiration water age of dominant vegetation at different altitudes from July 2020 to August 2021. After then, water age results and the MixSIAR source mixture model were combined to analyze the strategy of water utilization and seasonal changes. Simultaneously monitored included the air temperature and humidity, soil water content, root distribution and others. In the end, the seasonal changes of the transpiration water age and the water sources was analyzed with all the available data.

Important findings (1) Plants in Lushan area mainly use the seasonal precipitation, and the age of transpiration water is between 8.67 and 16.68 d. For the same genus of species, the transpiration water age of high altitude tree species is smaller than that of low altitude. Moreover, during the observation period, the water age of P. massoniana was “single valley-shaped” and P. taiwanensiswas “single peak-shaped”. (2) The low-altitude tree species mainly uses shallow soil water in the early rainy season. With the going-on of rainy season, the main water-absorbing layer moves down to the deep layer, and is stabilized in the deep soil in the late rainy season. However, in the late rainy season, the high-altitude tree species mainly use the water in the middle soil level. (3) In comparison, for the low-altitude trees, their water source is less dependent on shallow (0-20 cm) soil and absorbs more of deep (60-100 cm) soil water. High altitude is on the opposite.

Aims Canopy stomatal conductance (g_s) is an important indicator for measuring canopy atmospheric water vapor exchange. Studying its characteristics and responses to environmental factors could enhance the understanding of canopy water vapor exchange process and the comprehensive mechanism of environmental factors controlling forest canopy. Currently, differences in canopy stomatal conductance characteristics and its responses to environmental factors of the same tree species with different degradation degrees are still unclear.

Methods In the growing-season of 2019 (May-September), four types of Populus simonii stands with different degrees of degradation (non-degraded, mildly degraded, moderately degraded and severely degraded) in Zhangbei County of Bashang Plateau were selected, and thermal diffusion technology (TDP) probes were set to monitor trunk sap flow continuously. Environmental factors such as photosynthetically active radiation (PAR), vapor pressure deficit (VPD), air temperature (T), relative air humidity (RH) and soil water content (SWC) were monitored synchronously to analyze the sap flow rate and canopy stomatal conductance characteristics of P. simonii and their responses to environmental factors.

Important findings (1) The daily variation of sap flow rate in P. simonii showed a single-peak curve, while the g_s showed a double-peak curve. On the monthly scale, both sap flow rate and g_s showed a trend of increasing at first and declining subsequently, and then reaching the highest values in July. The differences in sap flow rate and g_s of P. simonii among the four stands of degradation degrees were significant in May and September. (2) The g_s was all affected by T, VPD and SWC. However, due to the differences in degradation, g_s in the non-degraded stands was mainly affected by T, VPD and 80-160 cm SWC. In the mildly degraded stands g_s was mainly affected by T, 0-80 cm SWC and VPD, and that in the moderately degraded was mainly affected by 0-80 cm SWC, T, VPD, while it in the severely degraded was mainly affected by T, PAR and VPD. (3) For the all P. simonii of different degradation degrees, the g_s above 18 °C was positively correlated with T. At 0.6-2.2 kPa, it was positively correlated with VPD, while negatively correlated with SWC. The g_s of the severely degraded P. simonii was positively correlated PAR when it was below 250 μmol·m^-2·s^-1. (4) Compared to the other three types of P. simonii, the severely degraded one had a more positive response to T changes and a lower sensitivity to other environmental factors. Due to morphological degradation, control of canopy transpiration of the severely degraded P. simonii will be even stricter to avoid further degradation or dieback.

Aims To study the effects of different nitrogen (N) addition levels and NH₄⁺-N to NO₃^--N ratios on photosynthetic characteristics and chlorophyll fluorescence parameters of Cunninghamia lanceolata will provid a scientific basis for the management of nitrogen fertilization in C. lanceolata.

Methods One-year-old seedlings of C. lanceolata were cultured in sands with three N addition levels of 0.5 (N₁), 1.0 (N₂), and 2.0 mmol·L^-1 (N₃) and seven different N form ratios (NH₄⁺-N to NO₃^--N ratios being as 10:0 (P₁), 8:2 (P₂), 6:4 (P₃), 5:5 (P₄), 4:6 (P₅), 2:8 (P₆), and 0:10 (P₇). The chlorophyll (Chl) content, photosynthetic characteristics, Chl fluorescence parameters and biomass in C. lanceolata were analyzed after 180 d treatment.

Important findings (1) The Chl a and Chl b content of C. lanceolata were the highest at P₂ and P₆ under N₁level, respectively. The Chl a, Chl b, and Chl (a+b) content were all highest at P₄ under N₂level. Both Chl a and Chl b content were the highest at P₃ among the seven ratios under N₃level. The Chl content showed an overall higher level of N₃ and N₂ than that of N₁ level. (2) The net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and water use efficiency (WUE) of C. lanceolata were all higher for higher NH₄⁺-N content than for higher NO₃^--N content. The P_n was the highest at P₁ under N₃ level, but the highest at P₂ under N₂ and N₁ levels. (3) The maximum photochemical efficiency of all treatments was in the normal range of 0.80-0.85, and the potential photochemical activity of photosystem II (PSII) was significantly higher under N₃ level than that of N₁ and N₂ at P₂. The fast chlorophyll fluorescence induction curve (OJIP) of leaves deviated greatly under N₁ level at P₁. P₁, P₂, and P₄ at N₂ and P₁, P₂, and P₅ at N₃gradually decreased at the I and P phases and gradually increased at the J phase. The apparent quantum flux per unit leaf cross-sectional area, heat dissipation capacity, and the number of active reaction centers per unit leaf cross-sectional area with the increase of nitrogen content at P₂ and P₃, while the absorption flux per reaction center (RC), electron transport flux per RC, trapped energy flux per RC, and dissipated energy flux per RC at P₆ decreased significantly with the increase of nitrogen content, the differences were not significant under the other ratios. (4) Total biomass and aboveground biomass of C. lanceolata were higher for higher NH₄⁺-N content than for higher NO₃^--N content, and significantly higher under the N₂P₂ treatment than under the other treatments. At the same N form ratio, it showed that N₂ > N₃ > N₁. The root-shoot ratio of N₁ and N₃ was significantly higher than that of other treatments, and the ratio of P₆ at N₂ level was significantly higher than that of other treatments, and the ratio of P₇ at N₂ level was significantly higher than that of N₂ and N₃. The photochemical reaction efficiency of C. lanceolata seedlings could be improved and the energy utilization of the PSII reaction center could be optimized by a higher N content and a higher ammonium to nitrate ratios, which would be more beneficial for photosynthesis and biomass accumulation.

Aims Water and nitrogen (N) availability are two of crucial factors affecting the growth of desert plants, and are sensitive to global climate change. With increasing N deposition and precipitation, the understanding of the responses of leaf N and phosphorus (P) stoichiometry of dominant species in sandy semi-shrub community could provide insights into the adaptive strategies of sand-fixing plants in the Mau Us Sandy Land.

Methods An experiment of N and water addition was conducted in an Artemisia ordosica community in the southern edge of the Mau Us Sandy Land. Soil available N and P concentrations, soil available N:P, leaf N and P concentrations, leaf N:P, and the corresponding homeostasis index of dominant species A. ordosica and Leymus secalinus were measured.

Important findings (1) Soil N and P availability and species identity jointly influenced the response of leaf N concentration, leaf P concentration, and leaf N:P in A. ordosica and L. secalinus to N and water addition, and the leaf N concentration of A. ordosica and L. secalinus showed different responses to treatments. (2) Both A. ordosica and L. secalinus showed higher stoichiometric homoeostasis indices for leaf P than for leaf N, which was closely related to the fact that the growth of A. ordosica and L. secalinuswere both N-limited. (3) The stoichiometric homoeostasis indices of leaf N concentration, leaf P concentration, and N:P in A. ordosica were relatively higher than those of L. secalinus, and A. ordosica adopted more conservative nutrient utilization strategies, while L. secalinus adopted more flexible nutrient utilization strategies. Therefore, A. ordosica was more competitive than L. secalinus in growth in arid and infertile environments. Under the scenarios of increasing N deposition and precipitation, the species composition of the A. ordosica community may change due to the contrasting competitiveness and nutrient utilization strategies between A. ordosica and L. secalinus.

Aims In the context of global climate change, drought-induced xylem embolism is considered as the main factor driving tree death. Therefore, analyzing the intrinsic anatomical determinants of xylem embolism resistance (water potential at 50% loss of xylem conductivity, P₅₀) is of great significance for understanding the mechanism between its structure and function, and provides a theoretical basis for the selection of tree species for vegetation restoration in the context of climate change.
Methods We measured the xylem vessel diameter, vessel grouping index, fractions of xylem tissues, pit morphology, pit membrane ultrastructure and water storage capacity (such as wood density and saturated water content), and explored the relationships between xylem embolism resistance and their anatomical structure and structural characteristics of 12 main evergreen tree species in Nonggang karst forest of Guangxi.
Important findings We found that: (1) P₅₀ had no significant correlation with vessel diameter, density, vessel grouping index and fraction of xylem tissues; (2) The correlations between P₅₀ and pit morphology, thickness of pit membrane and depth of pit chamber were not significant; (3) P₅₀ was negatively correlated with wood density and marginally positively correlated with saturated water content. Tree species with high wood density and low saturated water content had strong embolism resistance. The results indicated that using a single anatomical structure trait could not give out comprehensive evaluation on drought-induced embolic resistance. In addition, there was a trade-off between xylem water capacity and embolism resistance. This result was of great ecological significance for deeply understanding the internal structural mechanism of drought tolerance and diversified water use strategies of karst plants.

Aims The karst region encounters challenges such as low resistance to drought and delayed succession due to extensively exposed rocks and shallow soil layers, rendering the surface susceptible to dehydration. The study aims to investigate changes in hydraulic regulation strategies during different successional stages of species of subtropical karst forests. This exploration seeks to understand the mechanisms for adapting to drought following succession, and to establish a theoretical basis for vegetation restoration and reconstruction.

Methods The study centered on dominant species in forest communities along the early, middle, and late stages of succession in karst areas. Various hydraulic traits including the vulnerability of embolism in stems and leaves (P_50S and P_50L), the vulnerability segmentation (P_50L-S), the specific conductivity of stems and leaves (K_S and K_L), the hydraulic safety margin of leaf (HSM_L), density of sapwood, the Huber value, and the specific leaf area (SLA) were investigated.

Important findings (1) No trade-off was found between hydraulic safety and efficiency at either species or community level; P_50S, K_S, and K_L all decreased along the succession. (2) All species exhibited positive vulnerability segmentation, ranging from 0.53 to 6.59 MPa, and the vulnerability segmentation during early succession significantly exceeded those in the middle and late stages of succession. Furthermore, P_50S was identified as the primary determinant of the vulnerability segmentation. (3) The plants at early successional stage exhibited higher resistance to embolism, K_S, and K_L, which enhance the abilities of water transport and drought resistance. Conversely, in the later stage, plants showed larger SLA to improve competition for light resources. Our study reveals the patterns of adjustment of hydraulic regulation strategies, shifting from strategies aimed at improving hydraulic efficiency and safety to strategies aimed at increasing investment in photosynthetic carbon during the succession process of karst forest plants. This provides a theoretical basis to elucidate the mechanisms of adaptation to drought of plants in the succession process of karst forest communities.

Soil seed banks (SSBs) represent potential resource reserves for future species diversity in the terrestrial ecosystem, and play an important role in the storage of species and genetic diversity. Global changes and human activities have important impacts on SSBs, while current studies mainly focus on the response of SSBs to small scales (region) or single influencing factor. Comprehensive understanding on the responses of SSBs to global changes and human activities was limited by small scale (region) or lack of the multi-factor coupling. In this review, a total of 7 606 related articles were retrieved from databases of CNKI and Web of Science, ranging from 1980 to 9th February 2022, and bibliometrics were conducted to summarize the study progress and to guide the future study on the SSBs. The research outcomes of SSBs suggest that global changes (temperature, precipitation change and atmospheric nitrogen deposition) and human activities (soil use change, fenced, grazing and ecology restoration) have direct or indirect effects on the composition and size (density) of SSBs. The roles of SSBs in restoring degraded ecosystems remain unresolved. Four major research directions in SSBs still need to be paid more attention: (1) Standardize the sampling methods of SSBs, including sampling time, sampling size, and sampling depth, and establish a complete research methods systems; (2) Establish long-term field positioning observation and experimental station to study the change characteristics of SSBs on time and space scales; (3) Research on multi-factor interaction effects under global changes and human activities; (4) Based on the observation of long-term data, developing the models to predict and quantify the future restoration potential of SSBs to plant communities and ecosystems in the context of multiple factors.

Aims Betula platyphylla, as a typical pioneer tree species in temperate secondary forests, has important significance in forest growth research.

Methods In this study, microcoring method was used to continuously monitor the seasonal dynamics of radial growth of B. platyphylla in Changbai Mountains during two growing seasons (2020-2021), and the relationship between radial growth and environmental factors was analyzed.

Important findings The results indicated that the cambium of B. platyphylla became active in mid to late May, with June and July being the periods of rapid growth, and the lignification ended in late September. The increase of temperature in early spring in 2021 led to an early onset of cambial activity, but there was no significant difference in the time of radial growth cessation between the two years. During the rapid growth period, the radial growth rate of B. platyphylla showed a significant positive correlation with mean air temperature, minimum air temperature, relative air humidity and soil temperature, while it exhibited a significant negative correlation with the saturation vapor pressure deficit. During the slow growth period, the radial growth rate showed a significant positive correlation only with the minimum air temperature and soil temperature. In the drier year, the decrease of soil water content significantly inhibited radial growth of B. platyphylla. Temperature was the main factor affecting intra-annual radial growth. The findings of this study provide valuable insights for the sustainable management of B. platyphylla forests.

Aims Fine roots are important organs for absorbing and transporting nutrients during plant growth and development. Investigating the variation and trade-offs among functional traits of seedling fine roots of different mycorrhizal types is conducive to a more comprehensive understanding of their early survival strategies.

Methods In this study, we analyzed the variation and trade-offs across different mycorrhizal types, root orders and root functional modules. In particular, we measured three morphological traits (specific root length (SRL), root tissue density (RTD), and root diameter (D)), and four chemical traits (total phosphorus (P) content, total carbon (C) content, total nitrogen (N) content, carbon nitrogen ratio (C:N)), in three arbuscular mycorrhiza (AM) and three ectomycorrhiza (EM) tree species seedlings in mixed broadleaf-Korean pine (Pinus koraiensis) forest in the Liangshui National Nature Reserve, Heilongjiang Province.

Important findings The results showed that EM seedling fine roots exhibited higher RTD compared with AM seedlings, potentially due to the colonization patterns of AM fungi which increased root volumes and increased the absorptive capacity of limiting nutrients. Other traits did not differ significantly between the two types of mycorrhiza, with AM seedling roots aligning with a more resource-acquired strategy, in contrast to EM seedlings. As the root order increased, RTD and D of both mycorrhiza-association seedling roots increased significantly, while SRL decreased, indicating a functional shift from absorption to transportation. Concurrently, C content and C:N of roots increased, while the N content of roots decreased with increasing root order. A notable trade-off was observed between morphological and chemical traits of fine roots, suggesting that changes in root functional modules with root order are accompanied by corresponding shifts in root traits. These findings support the root economics spectrum (RES), highlighting the complex interplay between root morphology, chemistry and ecological strategy.