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.

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.

Aims As the core area of the ecological security barrier in northwest China, Xinjiang has been highly concerned for the spatial variations in its ecological environment status and quality and their driving mechanisms.

Methods Based on the MODIS surface albedo data set (MOD09 A1) from 2003 to 2020, this study uses the advanced three-band gradient difference vegetation index (advanced TGDVI) to obtain the fractional vegetation cover (FVC), and uses multiple statistical methods, such as linear regression, partial correlation analysis, Tukey-test to analyze the spatio-temporal variation of FVC and to quantify the contribution of temperature, precipitation, and groundwater storage (GWS) to FVC in Xinjiang.

Important findings (1) In the past 18 years, the average FVC of Xinjiang has increased from 20.08% to 21.76%, showing an increasing trend as a whole, with a growth rate of 0.19%∙a^-1, and a rapid growth stage is found after 2008. Among them, cropland has the largest growth rate (0.66%∙a^-1), and sparse grassland has the slowest growth rate (0.11%∙a^-1). (2) Temperature is an important factor affecting FVC in the whole growing season in Xinjiang. The influence of temperature on FVC is mainly concentrated in spring and autumn, while precipitation and GWS are the main factors in summer. (3) In summer, GWS is the main factor affecting FVC of shrubland and cropland, precipitation has the greatest impact on FVC of grassland, and GWS has a greater impact on FVC of sparse grassland in summer. (4) With the hydrothermal conditions becoming wetter, the influence of temperature on FVC in Xinjiang gradually decreases, while the influence of precipitation increases. The influence of GWS on FVC increased from arid to semi-arid condition, and then it decreased from semi-arid to humid condition. The results of this study could provide theoretical foundation for ecological restoration and construction in Xinjiang, and have great significance for promoting the construction of ecological civilization and green sustainable development in Xinjiang.

Aims In order to understand the development and evolution of xerophyte flora, it is important to explore the effects of the Quaternary climatic fluctuations and geological events on the distribution, genetic differentiation and evolution of Haloxylon ammodendron and H. persicum in the Gurbantünggüt Desert.

Methods Two chloroplast DNA spacers (trnS-trnG and trnV) were sequenced for 225 individuals from 19 naturally distributed H. ammodendron populations and 106 individuals from 12 H. persicum populations in Xinjiang. Haplotype Network analysis (Network), Principal Co-ordinates Analysis (PCoA), Analysis of Molecular Variance (AMOVA), Bayesian inference trees (BEAST), and Geographically weighted regression (GWR) were integrated to reveal the genetic diversity and environmental interpretation of different geographic populations within and between species, to estimate the time of interspecific lineage divergence and to analyze the demographical history.

Important findings (1) A total of 21 chloroplast haplotypes were identified, and H. ammodendron and H. persicum were clustered into independent clades. (2) Nearly 80% of the genetic variation occurred between species and among different geographical populations of H. ammodendron. The interspecies differentiation occurred from the late Pliocene to the early Pleistocene, which may have been affected by increasing aridity, mountain uplift on the Qingzang Plateau and desert expansion. (3) The results of the geographically weighted regression model showed distinct effects of the environmental factors on spatial heterogeneity of genetic diversity for H. ammodendron and H. persicum. On the whole, the climatic and soil factors had dominated the spatial pattern of genetic diversity for H. ammodendron and H. persicum. In the southern margin of the Gurbantünggüt Desert, climatic factors had positive effects on genetic diversity of H. ammodendron and H. persicum. In the southwestern margin of the desert, climatic factors had a positive effect on H. persicum, while soil factors had a negative effect on H. ammodendron. In the southeastern part of the desert, soil factors had a positive effect on H. ammodendron and a negative effect on H. persicum. In the Altay Region, climatic factors positively influenced both H. ammodendron and H. persicum.

Aims Seedlings play a crucial role in the conservation of forest biodiversity. Previous studies have paid little attention to seedling communities in monsoon broadleaf evergreen forests in Pu’er, Yunnan. Our aim was to investigate the mechanisms of seedling community assembly there.

Methods We analyzed the species composition of the seedling community based on the seedling survey in a 30 hm² forest dynamics plot. Seedling plots are divided into different groups according to the dominant species. The stepwise community assembly model (STEPCAM) was used to investigate the mechanisms of community assembly and to further analyze the functional traits of seedling communities.

Castanopsis echidnocarpa and C. calathiformis are the dominant seedling species in the monsoon broadleaf evergreen forest. Four plot types (i.e., C. echidnocarpa plot, C. calathiformis plot, mixed-dominant species plot, non-dominant species plot) were classified according to the presence or absence of dominant species. The seedling community assembly processes included: a) random dispersal assembly (with contribution rate 43.1%-61.3%); b) habitat filtering (with contribution rate 27.4%-33.9%); and c) limiting similarity (with contribution rate 5.7%-27.2%). The C. echidnocarpa and C. calathiformis plots were dominated by deterministic processes, with 56.9% and 54.6% contributions respectively, whereas the mixed-dominant and non-dominant species plots were dominated by stochastic processes, with 60.4% and 61.3% contributions respectively. Rao’s quadratic entropy (Rao’Q) was highest in the non-dominant species plot and lowest in the mixed-dominant species plot. The C. echidnocarpa plot has the lowest specific leaf area (SLA) and higher leaf thickness (LT), specific stem length (SSL), root mass fraction (RMF) and a maximum potential plant height (PPH), while the C. calathiformis plot and non-dominant species plot have a higher SLA. Among different seedling plots, the coefficients of variation for SSL and PPH were higher, while the coefficients of variation for other functional traits were lower. Multiple regression analysis showed that SLA and PPH were significantly and positively correlated with Rao’Q in different seedling plots. LT and life form were significantly and positively correlated with Rao’Q in other three types of plots, except for the non-dominant species plot. Thus, seedling community assembly in the monsoon broadleaf evergreen forest is driven by both stochastic and deterministic processes, and the contribution of the two processes varies with the type of seedling communities.

Aims Analyzing characteristics of the population and community is one of the most effective approaches to determining their endangered status. Listed as second-level endangered species, Acer miaotaiense was regarded as an extremely small population species. However, as details on the distribution and population characteristics of the species are lacking in Shennongjia area, the conservation of this species is severely constrained.

Methods This study investigated population and community characteristics of A. miaotaiense in Shennongjia area. We studied the population dynamics of the species by analyzing its age structure, static life table, and survival curve.

Important findings The results showed that: (1) there were 33 species of woody plants belonging to 15 families and 20 genera in the community, and the dominant species in the community were Juglans mandshurica, Carpinus cordata, Dipteronia sinensis and Corylus chinensis. (2) The relative importance value of A. miaotaiense was 2.23%, making it a non-dominant species in the community. (3) The distribution range of A. miaotaiense in Shennongjia was very narrow (about 1.7 hm²), and the population size was small (79 plants). (4) The proportion of young individuals of A. miaotaiense was relatively high (79.75%), indicating good regeneration. (5) The species survival curve belonged to the Deevey-II type, and the mortality rate of each age group of the population was similar. However, the mortality rate increased in the juvenile stage and peaked (62.5%) in the adult stage (12.5 cm ≤ diameter at breast height < 17.5 cm). (6) Fruiting individuals were rare, and a high percentage of seeds (58.15%) was non-viable, and resistance to external disturbance was low. In summary, the small population size, narrow distribution range, and low resistance to external disturbance are the likely factors contributing to the endangered status of A. miaotaiense in Shennongjia area. We believe that the population of A. miaotaiense in Shennongjia area is declining. Therefore, it is necessary to strengthen in situ conservation of the existing A. miaotaiense population, especially the young trees in the Shennongjia area. In the future, programs should be set up to monitor the population dynamics of the species and carry out seedling breeding for population restoration of the species.

Aims Populus pruinosa is a key species of desert riparian forest playing an irreplaceable role in eco-environmental protection in Tarim extremely arid region, China. Studies on variation pattern of ecological stoichiometric characteristics and homeostasis of plant and soil were helpful to understand the health status of desert vegetation and also provide insights into ecosystem nutrient cycling, and ecological strategies of organisms to environmental changes. The aim of the present study was to explore the variations of ecological stoichiometry of plant and soil carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric homeostasis of P. pruinosa leaves along groundwater depth (GWD) in Tarim basin.

Methods Through field investigation, we measured C, N, P contents in leaves of P. pruinosa and in soils. The differences between C, N, P contents and their stoichiometric ratios of leaves and soils as well as in stoichiometric homoeostasis were examined among sites with different groundwater depths.

Important findings With the increase of GWD, the N, P contents of leaves decreased and C content, C:N, C:P, N:P increased. The variation coefficient of all stoichiometric indices was basically low and that of C content was the lowest, but the difference among different GWD was significant. Leaf C content and C:P were significantly negative correlated with leaf N content, and leaf C:P and N:P were significantly negative correlated with leaf P content. Soil C, N, P contents and their stoichiometric ratios all decreased with the increase of GWD, and the variation coefficients of other indices except P content were high and significantly different among different GWDs. Soil P content was positively correlated with soil C and N contents. Moreover, the correlation of C, N, P stoichiometry between leaf and soil in shallow and middle GWD habitats were non-significant, while there were significant correlations between leaf P content, leaf N:P and soil stoichiometry indices in deep GWD habitats, and leaf C:N, C:P were higher in deep GWD habitats than that of other two habitats. It indicated that leaf stoichiometric characteristics were not directly determined by soil nutrient conditions, P. pruinoseimproved nutrient utilization to adapt arid adversity. The N and P stoichiometric homeostasis index (H) of P. pruinosa were ranked in the order of H_N > H_N:P > H_P. Combined with nutrient restriction diagnostic index (N:P), evidence suggested the growth of P. pruinosa was limited by P. Populus pruinosa maintained a relatively stable state of C content, N content, C:N, C:P with homeostasis regulation, adopting the conservative defense strategy to adapt to the increasingly arid environment. Therefore, adequate P supply should be considered during the restoration process in degraded desert riparian forests.

Aims As an important organ for plant nutrient acquisition and energy transport, fine roots are the most active and sensitive part of the root system. Their functional traits change along the environmental gradient, which can reflect plant resource acquisition strategies and adaptability to environmental changes. The purpose of this study was to analyze the effects of different nitrogen (N) addition levels on the morphological and chemical traits of the fine roots of Castanopsis hystrix, explore the plasticity of the fine roots of the species to short-term N addition, and provide theoretical support for clarifying and predicting the changes of root physiological function under global climate change.

Methods In January 2020, four treatments with different N addition levels were set up in the C. hystrix plantation, which were the control (CK, 0 kg·hm^-2·a^-1), low N treatment (LN, 50 kg·hm^-2·a^-1), medium N treatment (MN, 100 kg·hm^-2·a^-1) and high N treatment (HN, 150 kg·hm^-2·a^-1), with three replicates per treatment. Fine roots of C. hystrix were dug out by the excavation method, and traits of the 1st to 5th order fine roots in different N addition treatments were determined, including specific root length, specific root area, root tissue density, average root diameter and stoichiometry.

Important findings The results showed that, compared with the CK treatment, MN and HN treatments significantly reduced soil pH, HN treatment significantly increased soil NO₃^--N and total phosphorus contents. Nitrogen addition significantly increased the content of carbon (C) in the 1st order fine root. HN treatment significantly increased the C content of the 2nd order fine root. MN and HN treatments significantly increased the N content of the 1st and 2nd order fine root, and significantly decreased the C:N of the 2nd order fine root. There were no significant differences in specific root length, specific root surface area, root tissue density and average root diameter of fine roots under different N addition levels. Taken together, these results showed that short-term N addition mainly affected the element content and stoichiometric ratio of fine roots, but had no significant effect on the morphological traits of fine roots in the C. hystrix plantation. This finding will help to understand the response of forest nutrient cycling and C sequestration to global environmental changes in the southern subtropical region.

Tamarix ramosissima, as the main dominant plant species in arid deserts, has formed Tamarisk nebkhas during its long-term interaction with wind-sand. The study on water sources of T. ramosissima at nebkhas and its ratio to each water source can provide scientific basis for the conservation, restoration of native vegetation in arid desert areas.

Methods This study employed “space for time” methodology to clarify the water sources of T. ramosissimaat nebkhas, with the ratio of each water source quantified for T. ramosissima at different developmental stages of nebkhas, through field investigation and indoor model analysis.

Important findings (1) The soil moisture of T. ramosissimanebkhas varied with the nebkhas accumulation process. The average soil moisture in the 0-500 cm soil depth ranked in the order of: the embryonic stage (4.57%) > growth stage (4.46%) > decline stage (3.62%) > stable stage (3.48%). (2) The soil water content of the dunes increased significantly in the 40-180 cm layer during the embryonic and growth stages, and in the 180-360 and 360-500 cm layers during the stable and decline stages, respectively. (3) The soil water content and stable oxygen isotope ratio (δ¹⁸O) in the 0-40 cm layer of the nebkhas at each stage of development fluctuated significantly with seasonal changes, and the δ¹⁸O stabilized with increasing depth of the soil layer, indicating that the surface soil was influenced more by the external environment. (4) In spring, T. ramosissima mainly used the soil water in the 360-500 cm layer in the embryonic stage nebkhas, followed by the soil water in the 0-40 cm layer, with proportions of 53.1% and 21.4%, respectively; in the growth stage nebkhas, T. ramosissima mainly used soil water in 0-40 and 360-500 cm layers, with ratios of 53.1% and 23.0%, respectively; in the stable stage nebkhas, T. ramosissima mainly used soil water in 0-40 and 180-360 cm layers, with ratios of 49.8% and 29.3%, respectively; in the decline stage nebkhas, T. ramosissima mainly used soil water in the 360-500 cm layer, with a ratio of 60.9%. In summer, T. ramosissima mainly used soil water in the 360-500 cm layer in the embryonic and growth stage nebkhas, and the ratio was 61.1% and 42.8%, respectively. Tamarix ramosissima also used soil water in the 40-180 and 180-360 cm layers in the growing stage nebkhas; the use of soil water in each layer by T. ramosissima was uniform in the stable stage nebkhas; T. ramosissima mainly absorbed soil water in 180-360 and 360-500 cm layers in the decline stage nebkhas, with ratios of 29.0% and 44.1%, respectively. In autumn, the main water source of T. ramosissima on embryonic stage nebkhas was 360-500 cm soil water; soil water in 180-360 cm layer and 360-500 cm layer was the main water source for T. ramosissima in the grow and stable stage nebkhas; in the decline stage nebkhas, T. ramosissima mainly used soil water in 360-500 cm depth, and the ratio was as high as 92.3%, indicating that T. ramosissima showed different water use strategies in different development stages of nebkhas.

Nine uninhabited islands with different sizes, laying on the coast of Bohai Sea, were selected as research objects for a further understanding and study of the characteristics of plant communities. By using the method of sample plot survey, we investigated a total of 66 sample plots, covering the study of species composition, and the number of individuals, height and diameter at breast height (DBH) of woody plants, etc. 140 species of vascular plants belonging to 38 families and 98 genera were investigated through sampling plot method. The results showed that Asteraceae, Poaceae, Fabaceae were the most abundant families in the communities. Moreover, the native forest vegetation has been replaced by secondary ones dominated by Robinia pseudoacacia, Pinus thunbergii, Ailanthus altissima, and Ulmus macrocarpa, respectively. Meanwhile, temperate deciduous shrubland became zonal vegetation type in this area, and the representative communities are dominated by Ziziphus jujuba var. spinosa, Periploca sepium, Flueggea suffruticosa, Celastrus orbiculatus, respectively. And representative herbaceous alliances are dominated by Artemisia argyi, Suaeda salsa, A. capillaris, and Themeda triandra, respectively. In general, the species diversity of island plant communities is relatively low, belonging to vulnerable vegetation.