Aims Exploring the impact of climate warming on stoichiometric characteristics of trees is of significance for better understanding the response mechanism of trees to climate change.
Methods In 2004, we conducted a common garden experiment by transplanting Larix gmelinii trees from four provenances to a common garden near the warm edge of this species’ range in the Mao’ershan Ecological Station of China, in order to measure the concentrations of carbon (C), nitrogen (N) and phosphorus (P) in leaves of short branch, leaves of long branch, short branches, long branches, and fine roots at three diameter classes in response to warming.
Important findings The C, N, and P concentrations in leaves of short branch and roots of all diameter classes, and the N and P concentrations in leaves of old branch significantly differed among provenances. The provenances at high latitude sites were characterized by lower C and N concentrations and higher P concentration compared to those at low latitude sites. Warming treatment significantly increased the C concentration in all organs (except root at 1-2 mm diameter), and also significantly increased the N concentration in leaves, long branches and roots <1 mm diameter, and the P concentration in all organs (except short and long branches). The effect of warming on C and P concentrations decreased with the increasing warming, but increased for N concentration. The C:N, C:P and N:P in all organs (except short and long branches) significantly varied with provenances. The provenances at high latitude sites had higher C:N and lower C:P and N:P compared to those at low latitude sites. Warming treatment significantly decreased the C:N, C:P and N:P in all organs except short and long branches. In summary, the stoichiometric characteristics had evident geographical variations in resource acquisition organs of leaves and roots of L. gmelinii. Warming treatment mainly alleviated the constraints on the demand for N and P in leaves and roots, and simultaneously reduced the C sequestration efficiency of N and P. The impact of climate warming on the stoichiometric characteristics of C and P elements decreased as the increasing warming, except N element.

The leaves and fine roots are the most sensitive and active parts of the above- and below-ground parts of plants, respectively, and they play a very important role in the carbon cycle of the forest ecosystem. The physiological and metabolic characteristics of leaves and fine roots, and their interrelated changes not only reflect the growth status of plants under the background of global warming, but also reveal the response characteristics and adaptation strategies of plants to environmental stress. Their changes have become one of the hotspots and difficulties in the field of global change. A large number of experiments has been carried out domestically and abroad to investigate the change characteristics and response mechanisms in physiological metabolism and of plant leaves and fine roots under global warming conditions from the perspectives of oxidative damage, antioxidant defense and metabolites. At present, some studies found that atmospheric warming will promote the accumulation of active oxygen species in leaves and caused oxidative damage to leaves, while the damage to fine roots is not obvious. But some other studies also showed that fine roots are more affected by soil warming. In summary, how plant leaves and fine roots will respond to climate warming by adjusting their physiological and metabolic characteristics and the interaction between organs and the internal mechanism of these responses have not been fully studied. So, this study systematically reviewed the research progress on the oxidative damage and antioxidant defense characteristics of plant leaves and fine roots under the background of global warming and their interrelated changes, with a view to providing a reference for the research on the response and adaptation mechanism of plants to global warming, and suggest that the following aspects should be carried out in the future: (1) more study on oxidative damage and defense characteristics of plants by warming at population and community scales; (2) combined above- and below-ground phenological characteristics to study the effect of warming on oxidative damage and defense characteristics of plants; (3) deeply analysis on the response of plant oxidative damage and defense characteristics to warming from the correlation between more plant physiological indicators; (4) more concern on the correlation between above- and below-ground of plants, and their seasonal differences.

Aims Both the carbon cycle and the function of grassland ecosystem as a carbon sink are impacted by the rising nitrogen deposition. Active organic carbon content is an important measure that can reveal changes in soil carbon pool. For a thorough understanding of carbon cycling and the creation of sensible ecosystem management strategies, it is essential to investigate the impacts of nitrogen addition on the active organic carbon fractions of grassland soils.

Methods Five different nitrogen addition treatments were set up in a temperate typical steppe of Nei Mongol. Soil organic carbon fractions content, soil physical and chemical properties, aggregate stability, microbial activities and extracellular enzyme activities were measured. Pearson correlation and structural equation model (SEM) were used to examine the relationships.

Important findings Nitrogen addition reduced the contents of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidizable organic carbon (EOC). The contents of DOC, MBC, and EOC all decreased with the increases of soil depth. The treatment of 5 g·m^-2·a^-1 nitrogen addition significantly promoted the decomposition of active organic carbon fractions. The effect of nitrogen addition on soil active organic carbon fractions content was regulated by biotic (microbial biomass, extracellular enzyme activity, etc.) and abiotic (soil physical and chemical properties, aggregate stability, etc.) factors. Nitrogen addition reduced soil density, increased mean mass diameter and the proportion of large aggregates, increased the contact between organic matter and substrate, promoted the decomposition of active organic carbon, and reduced the contents of DOC and EOC. Nitrogen addition inhibited the activities of polyphenol oxidase and peroxidase, reduced the decomposition of difficult-to-decompose organic matter and the contents of EOC and MBC. Nitrogen addition increased the activities of β-glucosidase and cellulose hydrolase, promoted the utilization of DOC by microorganisms, and reduced the content of DOC. Our results indicated that nitrogen addition treatment can affect the decomposition process of active organic carbon by changing soil physicochemical properties and the secretion of extracellular enzymes from microorganisms, promoting the release of carbon in grassland soils. This provided a theoretical basis for further exploration of grassland soil carbon dynamics under nutrient addition in the future.

Songhua River basin, encompassing numerous vital ecological protection areas and water conservation zones, is crucial in facilitating sustainable economic development in Northeast China. The basin exhibits a complex array of land use types, resulting in a diverse ecosystem. The dynamic monitoring of watershed-scale land use/land cover changes (LULCC) and carbon stocks estimation of the terrestrial ecosystem can provide suggestions for optimizing land utilization, enhancing terrestrial ecosystem carbon storage, and achieving the objective of "dual carbon". 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/land cover maps of the Songhua River Basin with high accuracy and conducted dy-namic monitoring of LULCC and its ecosystem carbon storage using an Integrated Valuation of Ecosystem Ser-vices and Trade-offs model, Mann-Kendall tests and Theil-Sen Median trend analysis. Results showed that farm-land 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 1986-2022 period, the farmland expanded 11462.68 km2 while forest land decreased 18567.21 km2; the construction land experienced the largest change rate of 5.3% with an increased area of 3505.82 km2; the change rate of the sparse forest is 4.7%, ranking the 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 5385.43 km2. There was evident spatial heterogeneity in the distribution of the terrestrial ecosystem carbon stocks within the Songhua basin, with high carbon stocks predominantly found in the Dax-ingan and Xiaoxingan as well as the Changbai Mountains. The median carbon stock values were observed in 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, pri-marily concentrated in the regions initially characterized by high carbon stock values. However, the area with increased carbon stock is scatterly located 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 forestland and continue im-plementing forestry projects to effectively prevent further depletion of terrestrial ecosystem carbon storage in the Songhua River basin.

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.

Aims Studies on the adaptation of plant biomass and nitrogen use efficiency (NUE) to atmospheric nitrogen (N) deposition were helpful to understand the changes of carbon (C) and N cycling in terrestrial ecosystems under the background of global N deposition. However, the effects of N addition on plant biomass and NUE and the main factors affecting these responses remained unclear. Our objective was to explore the responses of biomass and NUE in the whole and different components of plants to N addition.

Methods We conducted a meta-analysis by collecting data from 94 publications focusing on N addition in China, to quantitatively assess the effects of N addition on biomass allocation and NUE of plants, as well as the main influencing factors.

Important findings The results showed that: (1) N addition significantly increased total, aboveground, and belowground biomass while significantly decreased the NUE of different components. Plant aboveground biomass (34.0%) increased more than that of belowground biomass (5.3%), and the decreased belowground NUE (29.9%) was higher than that of aboveground (15.4%). (2) The responses of plant biomass and NUE to N addition varied across ecosystem types, N forms, N addition levels, duration, and water conditions. The responses of plant in grassland and desert to N addition were significantly higher than that in other ecosystems. (3) Soil total N content was the most important factor affecting the responses of plant total, aboveground, and belowground biomass. The responses of plant and aboveground NUE were mainly modulated by N addition rate, and the form of N fertilizer mainly influenced the responses of belowground NUE. In conclusion, the effects of N addition on plant biomass and NUE were opposite, and they were mainly affected by soil total N content and N addition rate, respectively. These findings may provide reference for further research and practice on the distribution and utilization of C and N in plants under the background of N deposition.

Aims Nei Mongol is an important ecological security barrier in northern China, and the study of changes in its vegetation productivity is of great significance to the ecological security of the northern region.

Methods Based on multi-source remote sensing data such as Eddy Covariance-Light Use Efficiency Gross Primary Productivity (EC-LUE GPP) in Nei Mongol from 1982 to 2017, this paper uses trend analysis and correlation analysis to analyze the temporal and spatial variation characteristics of vegetation gross primary production (GPP) in Nei Mongol and its correlation with air temperature, precipitation and soil moisture. On this basis, multiple linear regression and residual analysis methods were used to decompose and quantify GPP under the influence of climate changes and human activities, divide different time periods to carry out its impact on vegetation GPP, and explore the impact of different vegetation types on the driving factors response.

Important findings (1) Three meteorological elements showed good correlation with vegetation GPP, among which precipitation and soil moisture had higher correlations with GPP. (2) During the period 1982-1990, vegetation GPP showed an insignificant increasing trend with large fluctuations and the remaining three time periods (1991-2000, 2001-2010, 2011-2017) showed an insignificant downward trend. The areas with an overall downward trend accounted for 55% of the total area, and the other 45% showed a significant upward trend. (3) Except for the period from 2001 to 2010, climate changes played a decisive role in vegetation restoration in the other three time periods (1982-1990, 1991-2000, 2011-2017), explaining 20%, 16% and 13% of vegetation restoration, respectively. Human activities dominated vegetation degradation areas, explaining 13%, 19% and 20% of vegetation degradation, respectively. The research results can provide scientific reference for the implementation of ecological environmental protection and management policies and green and sustainable development in Nei Mongol.

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

Aims Carbon sequestration in terrestrial ecosystems is one of the important ways to slow down the rise of atmospheric CO₂ concentration. Therefore, understanding the natural vegetation ecosystems carbon storage (ECS) in response of future climate change is critical for making of regional land management policies.
Methods In this study, the sensitive parameters of LPJ-GUESS model are calibrated based on genetic algorithm. Using the downscale climate data-driven model, combined with Mann Kendall test, Sen’s slope estimation and partial correlation analysis, the temporal and spatial patterns, trend change characteristics and climate dominant factors of China’s ECS from 2001 to 2100 are analyzed.
Important findings The Nash-Sutcliffe efficiency coefficient and Pearson correlation coefficient of the calibrated LPJ-GUESS model in simulating ECS are 0.751 and 0.901, respectively, indicating that the LPJ-GUESS model can simulate China’s ECS well. During 2001-2020, China’s ECS decreased from southeast to northwest, with a total amount of 156.06 Pg. Vegetation, litter and soil carbon storage accounted for 34.2%, 1.9% and 63.8% of total ECS, respectively. The ECS in 2081-2100 shows similar spatial pattern with that in historical periods. The total amount of ECS at the end of this century are expected to increase by 0.51-11.16 Pg. The growth rates of China’s ECS was 8.5 g·m^-2·a^-1 and 3.7-21.0 g·m^-2·a^-1 during 2001-2020 and 2021-2100, respectively. During 2021-2100, significant increases of ECS are observed in southeast China, Nei Mongol Plateau, Qingzang Plateau (37-44 g·m^-2·a^-1), while obvious decreases (45-72 g·m^-2·a^-1, in the southern Yunnan-Guizhou Plateau, hilly areas in Guangxi and Guangdong. In northwest China, temperature is the dominant factor affecting ECS. The influences of precipitation on ECS are strengthened from the southeast to northwest. In high latitude and high-altitude areas, radiation is the dominant factor of ECS. CO₂ plays the most important role on ECS across about 47.9%-56.1% of China’s area.

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

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

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

Aims Meteorological data show faster warming of the global land surface during the night than during the day in the past 50 years. However, most of the previous studies were focused on the effects of whole-day equivalent warming, and the understanding of effects of diurnal asymmetric warming remains elusive.
Methods This study evaluated the effects of diurnal asymmetric warming on carbon sink capacity using a optimization model considering photosynthetic gain and hydraulic cost in a broadleaf Korean pine (Pinus koraiensis) forest in Changbai Mountains.
Important findings Results show that the model simulations matched well with observations of net primary production based on the data measured from eddy covariance flux towers. Warming promoted carbon sequestration (11.2%-13.8%) in our study area but did not significantly affect the water use efficiency, and the positive effects on annual carbon sequestration had no statistical difference among different warming scenarios. In addition, warming increased the water stress for forest plants, subsequently increasing the loss percentage of conductivity (PLC, hydraulic vulnerability; 1.1%). In conclusion, all warming scenarios significantly enhanced the current carbon sink capacity of forests compared with ambient condition, but warming may increase the risk of forest death through hydraulic failure, which would significantly affect the future forest carbon sink.

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

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

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

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

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

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

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

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

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

Aims This study investigated the spatial and temporal variation of spring and autumn photosynthetic phenology of vegetation in the Dongting Lake basin and revealed its response to climate change, and provides a useful reference for the establishment of model of subtropical vegetation phenology and the evaluation of carbon budget.

Methods Using solar-induced chlorophyll fluorescence (SIF) data, we extracted spring photosynthetic phenology (the start date of photosynthesis) and autumn photosynthetic phenology (the end date of photosynthesis) of vegetation in Dongting Lake basin, and evaluated temporal and spatial patterns of vegetation spring and autumn photosynthetic phenology and its response to climate change.

Important findings (1) From 2000 to 2018, the vegetation spring photosynthetic phenology was significantly advanced at the rate of 0.75 d·a^-1, the autumn photosynthetic phenology was delayed at the rate of 0.17 d·a^-1, and the vegetation growing season length was significantly prolonged at the rate of 0.90 d·a^-1. (2) The preseason maximum air temperature and minimum air temperature were the main factors affecting the advance of spring photosynthetic phenology. The autumn photosynthetic phenology of vegetation was positively correlated with preseason precipitation, minimum air temperature and radiation intensity, but negatively correlated with preseason maximum air temperature. (3) In addition, we found that the spring photosynthetic phenology of vegetation in the study area was more sensitive to climate change, especially the increase of preseason minimum air temperature led to the significant advance of spring photosynthetic phenology of evergreen needleleaf forest, evergreen broadleaf forest, bush and grassland. In conclusion, the advance of vegetation spring photosynthetic phenology in Dongting Lake basin played a dominant role in prolonging the growth season, indicating that spring photosynthetic phenology plays a more important role in enhancing the carbon sink function than the autumn photosynthetic phenology in the context of global warming. The vegetation spring photosynthetic phenology was more sensitive to climate change and the air temperature was the main factor controlling the vegetation spring photosynthetic phenology, which provides a scientific basis for the simulation and prediction of evergreen vegetation phenology.

Aims Global climate change has aggravated the effects of drought which is one of the major factors restricting the sustainable development of agriculture and forestry. It is important to study the growth performance and the changes of physiological mechanism of dioecious plants during drought and rewatering process, which could help to understand the difference of adaptability and stress tolerance to the unfavorable environment in dioecious plants. And this paper also provides a theoretical basis for the selection of tree species for afforestation in the context of global climate change.

Methods Male and female cuttings of Populus deltoides were planted in the pots in a greenhouse, and were treated by drought stress and rewatering. The growth, leaf water parameters, and photosynthetic parameters were measured to analyze the physiological adaptability and stress tolerance of males and females under drought-rewatering conditions.

Important findings Drought stress showed negative effects on plant growth by reducing the growth of plant height and basal diameter, with decreased relative water content, water potential, net photosynthetic rate, stomatal conductance, transpiration rate, photosynthetic electron yield, photochemical quenching coefficient and electron transfer rate of leaves of males and females. There were no significant sexual differences in all parameters between males and females under sufficient water supply. Under drought stress, the growth of male plants was better than that of females, with higher growth rate of plant height and more root biomass accumulation in males. Drought resulted in the decrease of the maximum photochemical efficiency and the potential activity of photosystem II (PSII), and the increase of the intercellular CO₂ concentration of females. PSII of male plants was less damaged under drought conditions, and the photosynthetic reaction center still maintained a high light-harvesting efficiency. Meanwhile, alternating oxidase (AOX) activity was significantly increased in roots and leaves of male seedlings, which could alleviate the effect of photoinhibition. All indexes recovered after 30 days of rewatering. However, the growth rate of plant height and ground diameter, and net photosynthetic rate of males and females under drought stress were significantly lower than those of the control group without drought stress. The results showed that the growth of male and female seedlings of P. deltoides was inhibited by drought stress, and the females were more likely affected by water deficit. Water stress induced a series of adaptive physiological effects in males, including decreased leaf relative water content, decreased photosynthetic and chlorophyll fluorescence parameters, and increased activity of alternating oxidase. Therefore, males had a more effective protective mechanism than females, which was also conducive to the recovery of various functions after rewatering.

Aims The objective of this study was to reveal the effects of climate warming on fine root dynamics of a plantation in subtropical China.

Methods An in situ soil warming experiment in a mature Cunninghamia lanceolataplantation was conducted at the Fujian Sanming Forest Ecosystem National Observation and Research Station. The effects of soil warming on the growth, morphology and physiological metabolism characteristics of fine roots in this mature plantation in different seasons were investigated by using the in-growth core method.

Important findings In the rainy season, warming significantly increased the growth of 0-1 mm fine roots and total fine roots (0-2 mm) by 109.9 % and 78.2% respectively, and also increased the specific root length (SRL) and soluble sugar content of 0-1 mm fine roots by 28.8% and 41.5% respectively, compared with the control. However, warming significantly decreased the root specific respiration rate (SRR) and starch content of total fine roots by 64.1% and 15.9% respectively. In the dry season, there were no significant changes in the growth and morphological indices of 0-1 mm and 1-2 mm fine roots after warming, while the SRR of 0-1 mm fine roots and the contents of starch and non-structural carbohydrates (NSC) of 1-2 mm fine roots were significantly reduced by 60.7%, 43.9% and 14.2% respectively. Therefore, under future climate warming, the mature C. lanceolata plantation may have strong adaptability in the subtropical region. During the rainy season, the mature C. lanceolata plantation maintains normal physiological activities by increasing fine root SRL to absorb more resources and promoting the transformation of starch to soluble sugar, so as to promote the growth of fine roots in response to warming. In the dry season, the mature C. lanceolata plantation responds to the warming by reducing the SRR of fine roots to reduce internal nutrient depletion and increasing the NSC utilization to improve water transport efficiency to maintain normal fine root growth; adjusting the SRL, specific root surface area and root tissue density of fine roots may not be the main strategies for the mature C. lanceolata plantation in response to warming.

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

Aims The response of plant phenology to climate warming is an important element of global change research. At present, studies on plant phenology response to climate warming are in severe shortage for high-altitude ecosystems, especially regarding responses to multiple-level warming.

Methods We conducted a multiple-level warming experiment in an alpine meadow on Qingzang Plateau, and monitored plant phenology of two dominant species, including the timing of green up, budding and flowering in 2015, 2017, 2018 and 2021.

Important findings The results showed that plant phenology of different species exhibited various trends under warming. For Kobresia pygmaea, delay in phenological development, including green up, budding and flowering, was positively correlated with temperature increases. However, the timing of phenological stages of Potentilla saundersiana showed advancing first, and then delay with increasing temperature. These results suggest that plant phenology of alpine meadow asynchronously responds to increased temperature. In addition, temperature increase exerts delayed effects on plant phenology over long-term. The structural equation modeling showed that temperature increase consistently delayed the green up of K. pygmaea, and low-level warming advanced phenological development of P. saundersiana, but this advancing trend reversed under high-level warming. Importantly, soil moisture plays a key role in determining the magnitude and direction of phenological response to climate warming in our study. Our findings indicate the asynchronous characteristics of plant phenology response to climate warming in alpine meadow ecosystems, and provide basis to predict responses of high-altitude ecosystems to climate change in the future.

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

Aims Nitrogen addition and extended dry season can profoundly affect non-structural carbohydrates (NSCs), carbon (C), nitrogen (N) and phosphorus (P) concentrations, and biomass of plants, however, the different responses of various organs (leaf, trunk, stem and root) in the same plants are not clear. We thus explored such responses to N addition and extended dry season to help better predict plant growth under global changes.

Methods The investigation was conducted with Dalbergia odorifera seedlings through a manipulated N and water experiment. The concentrations of NSCs and C, N, and P and allocation pattern of biomass in different organs of D. odorifera seedling were determined, and then compared among different treatments.

Important findings (1) N addition significantly increased trunk NSCs concentrations, while the interaction of N addition and extended dry season significantly decreased NSCs concentrations. N addition, extended dry season and their interaction significantly increased root soluble sugar concentrations. (2) N addition significantly increased root N concentrations and decreased C:N, and the interaction of N addition and extended dry season significantly decreased C:P and N:P in trunks. (3) All treatments did not influence the total biomass of D. odorifera, but significantly decreased the ratio of leaf biomass to total biomass, and N addition and extended dry season significantly decreased the ratio of root biomass to shoot biomass but increased the ratio of stem biomass to leaf biomass. Overall, N addition may promote the growth of seedling trunks and improve the economic value of D. odoriferaunder the extended dry season in the future. In order to prevent the growth of D. odorifera from being inhibited under drought stress, it is necessary to replenish an appropriate amount of water in the dry season.

Aims Vulnerability segmentation is one of physiological mechanisms underlying drought resistance for tree species. The aim of this study is to clarify the patterns of vulnerability segmentation and its physiological significance for woody species from drought-prone tropical and subtropical karst forests.

Methods A total of 57 typical woody species were selected from tropical and subtropical karst forests. We measured their leaf and stem vulnerability curves and minimum water potential to calculate vulnerability segmentation (P50_leaf-stemis the difference in cavitation resistance between leaf and stem, with larger values indicating stronger vulnerability segmentation) and hydraulic safety margin. We compared the differences in P50_leaf-stem between different plant taxa and explored the relationships between P50_leaf-stem and hydraulic safety margin.

Important findings (1) The P50_leaf-stem across the woody species ranged from -1.28 MPa to 4.63 MPa, with an average value of 1.32 MPa. Out of the 57 species, 49 species showed a positive P50_leaf-stem. (2) Shrub species showed higher P50_leaf-stem than tree species, and species from karst ridge showed higher P50_leaf-stem than those from karst valley. However, there was no significant difference in P50_leaf-stem between evergreen and deciduous species. (3) During the drought period, species with higher P50_leaf-stem tended to have smaller leaf hydraulic safety margin but larger stem hydraulic safety margin, indicating that occurrence of cavitation in leaves can reduce hydraulic risks of stems. This study confirms that vulnerability segmentation is an important hydraulic strategy for most tropical and subtropical karst woody species to deal with drought stress.

The fine root phenology of forests is an important indicator to observe the impact of global warming. It can reflect not only the growth status of forests under the background of global change but also the dynamics of the carbon cycle and below-ground carbon distribution of terrestrial ecosystems. Meanwhile, the response of forest fine root phenology to climate change is considered a hotspot and challenge in the field of global change effects, and thus has been studied extensively. Recent studies claim that soil warming will prolong the growing season of fine roots in forests as the spring phenology and growth peak will begin earlier in some areas of the northern hemisphere, however, atmospheric warming may inhibit the growth of fine roots and delay the phenological events. In addition, some studies found that the root phenology in the surface soil may be more affected by warming than that in the deep layer. Concurrently, some researchers associated fine root phenology with rhizosphere soil environment, microorganisms and above-ground phenology to reveal the response mechanism. However, the response of fine root phenology to climate warming and its underlying mechanisms have not been fully explained. This paper systematically reviewed changes in fine root phenology in forests under global warming, and aimed to provide references for the research on below-ground phenology, and the response and adaptation mechanism of forests to global changes. Future studies should enhance the research on the following aspects: 1) improving and exploring more accurate simulation warming devices and carrying out long-term quantitative research; 2) exploring the relationship between different functional modules of roots (such as absorbing root/transporting root, fibrous root/pioneering root) and their phenology under changing environments, i.e. “environment-traits- phenology”; 3) considering variations of the control factors of root phenology under different below-ground phenological phases (the beginning, peak and end of root growth), species and soil layers; 4) focusing on the relationship between below- and above-ground phenology, and its impacts on plant productivity; 5) focus on the changes of forest below-ground phenology and ecosystem functions (such as carbon sinks, nutrient cycling, etc.) under the combined effect of warming and other environmental factors (CO₂ concentration, nitrogen deposition, etc.).

Aims Along with intensified climatic warming and human activities, global arid areas have expanded in an unprecedented rate during the past decades. Dryland ecosystems have witnessed increased vulnerability and sensitivity to climate change. Exploring the time lag effect of climate change on dryland vegetation growth is becoming an important research highlight in current global change related studies.

Methods In this study, we synthesized the normalized difference vegetation index (NDVI) from Moderate- resolution Imaging Spectroradiometer (MODIS), the monthly gridded CRU TS4.05 (Climatic Research Unit Time-Series version 4.05) climate and drought information developed by the University of East Anglia, solar radiation information from ERA5 (ECMWF’s Fifth Generation Atmospheric Reanalysis of the Global Climate) and soil moisture information from the European Space Agency (ESA) Climate Change Initiative program (CCI). These data were designed to investigate the effects of climatic factors and their time-lag on grassland NDVI in Asian grasslands from 2001 to 2020. This analysis was conducted based on the window cross-correlation and one-dimensional linear regression.

Important findings Our study revealed that: 1) The grassland NDVI responded strongly to average temperature and total precipitation when there was no lag, but expressed a lag response to solar radiation and soil moisture (1-month). 2) The spatial distributions of the lag response of grassland NDVI to climate change were nonuniform, with significant differences observed between the western and eastern Asian grasslands. 3) We did not detect any apparent time-lag effects on interactions between grassland NDVI and self-calibrating Palmer Drought Index. 4) We argue that altitude could partly modulate the response of grassland NDVI to climatic variables in the grassland of Asian drylands.

For the universal grassland degradation and associated human utilization in the world, authors expound ecosystem restoration, climate climax in ecological succession, environment change and grassland state transition, grazing and disturbance climax, restoration by human intervention, thereby put forward the restoration path and state model of the degraded grassland ecosystem. This paper emphasizes that the restoration of degraded grassland should be carried out from the perspective of ecosystem, rather than only vegetation or soil processes, because there will be multiple alternative restoration states for grasslands in the context of environmental change or human disturbance. Three basic restoration modes of degraded grassland and possible restoration states are described as the followings: (1) Gradual restoration according to natural succession: based on the theory of ecological succession, grasslands from light to moderate degradation under favorable environments might reach the climax or near climax state for a long time by the systematical self-organization. (2) Intervention restoration by human activity: for those severely or extremely degraded grasslands, it needs to break through a series of abiotic (soil structure, nutrients, etc.) and biotic (plant colonization, species interaction, etc.) restrictions, and restore to a certain equilibrium or stable state, even climax state by using engineering, physical, chemical or biological-ecological methods or practices. It will take a long-time. (3) Restoration by grazing disturbance: grassland ecosystem structure (species composition and diversity), productivity and nutrient processes could be regulated through light to moderate livestock grazing, thereby maintaining and promoting grassland ecosystem multifunctionality and stability. This restoration method can be selected for medium-mild degraded grasslands. In conclusion, the holistic goal of grassland restoration is to achieve its long-term stable ecosystem multifunctionality.

Aims How nitrogen (N) addition impacts the emission of greenhouse gases (GHGs) is now becoming a hot issue in the study of global change. We aim to delineate the effects of N addition on the emission of major greenhouse gases (CO₂, CH₄and N₂O).

Methods In order to achieve this goal, the flux of the three major GHGs was measured using static chamber gas chromatography during the growing seasons (May through September) of 2020 and 2021 in a meadow steppe of Hulun Buir in Nei Mongol. The experiment was conducted by applying NH₄NO₃ to simulate the atmospheric N deposition, which involved six N addition levels (i.e., 0, 2, 5, 10, 20, 50 g·m^-2·a^-1) and two grassland utilization levels (i.e., mown and unmown).

Important findings The results showed that the response of the three GHGs to N addition showed clear nonlinear patterns, but there was a remarkable difference in the patterns among the three GHGs. The emission of CO₂ was increased with increasing N addition but saturated at around 10 g·m^-2·a^-1. The uptake of CH₄ was promoted with increasing N addition when N addition was low (0-5 g·m^-2·a^-1), but this promotion effect was diminished with further increase in N addition (5-10 g·m^-2·a^-1), and the uptake of CH₄ was inhibited when N addition reached 50 g·m^-2·a^-1. The emission of N₂O increased significantly with the increase of N addition rates, but the response patterns and amplitude showed remarkable difference between the two years. With the data in the two years pooled, the CO₂ flux had a significant positive correlation with precipitation and nitrate nitrogen (NO- 3-N) content, and a significant negative correlation with pH; CH₄ absorption flux was significantly positively correlated with precipitation and ammonium nitrogen (NH+ 4-N) content, while negatively correlated with pH; N₂O flux was significantly positively correlated with soil temperature and NH+ 4-N content, while significantly negatively correlated with NO- 3-N content. Our findings demonstrated that the response of the three GHGs to increasing atmospheric N deposition was largely nonlinear, and the response patterns were remarkably different among the three GHGs. These findings may be of great importance for controlling N fertilizer use, selecting appropriate grassland use, and evaluating grassland ecosystem warming potential under increasing atmospheric N deposition.

Aims Seasonal drought often occurs in the northern rocky mountainous area due to annual variation in precipitation. Exploring the effects of changes in precipitation on the sap flow characteristics and water sources of Platycladus orientalis is of great significance for structuring a stable ecosystem.

Methods In this study, the plantation of P. orientalis in the rocky mountainous area of Beijing was taken as the research target. The thermal dissipation probe (TDP) and hydrogen/oxygen isotope tracer technology were used to observe the P. orientalisunder different watering treatments. Meteorological, soil moisture, and other environmental factors were simultaneously monitored.

Important findings The results showed that natural precipitation and double precipitation > half precipitation > no precipitation were the main characteristics of P. orientalis sap flow. Precipitation increased the relative effective water content (REW) of soil, thereby stimulated the response of P. orientalis sap flow to environmental factors. Platycladus orientalis sap flow is mainly affected by the atmospheric vapor pressure deficit (VPD), and the impact of solar radiation (R_s) and wind speed (WS) is relatively low. The water source of P. orientalis changed with precipitation amounts. When the soil water content increased, its water source gradually changed to shallow soil. Compared with precipitation before, P. orientalis have increased the utilization ratio of 0-40 cm soil water after precipitation, except that P. orientalis in no precipitation treatment that exhibited no noticeable change. This change is more pronounced in natural precipitation and double precipitation treatments where a period of high relative water content after precipitation was more evident. To sum up, P. orientalis can adjust sap flow and the depth of water absorption from soil in responses to the changes in precipitation and soil moisture. This self-adaptive characteristic is conducive for trees to survive the extreme drought.

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

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

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

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

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

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

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

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

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

Aims Current research on the maintenance mechanisms of forest biodiversity mainly focuses on the stage of examining the abundance of aboveground organisms. However, many gaps remain in our knowledge of interactions between species and on whether the underground fungi affect the maintenance of biodiversity. This study explores the role of soil fungi in maintenance of biodiversity and the relationship between plant-soil feedbacks and plant growth. We selected four tree species in a broadleaved Korean pine forest in Northeast China, and used controlled seedling planting experiments to test the Janzen-Connell hypothesis.

Methods Experimental treatments included fungicide application and controlled seedling planting of four tree species (Pinus koraiensis, Fraxinus mandshurica, Phellodendron amurenseand Tilia amurensis) in Jiaohe forest farm, Jilin Province. Biotic and specific feedbacks were assessed using the fungicide treatment and the control seedling planting of different tree species. Soil fungal diversity was determined by high-throughput sequencing method and tested for differences among different treatments. The relationships of the two feedback types with tree species, functional types of fungi and soil were analyzed by variance partitioning analysis (VPA).

Important findings Fungicide treatment did not significantly affect the biotic feedback, and seedling biomass in conspecific soil did not show significant distance dependence. The specific feedbacks were not significantly improved by presence of different tree species. In addition, VPA showed that the most important factor affecting plant-soil feedbacks was inherent species characteristics, with the influence of soil and fungi varying with the feedback type. This study identified the factors influencing plant-soil feedbacks in mixed forest of temperate zone, and demonstrated the variability of Janzen-Connell hypothesis with temperate forest tree species, laying a foundation for better understanding the interactions between species and the underlying regulation mechanisms.

Aims Forest ecosystem changes with time in response to environmental fluctuations and disturbances, and the research on its stability and influence mechanism is conducive to maintaining ecosystem services. The temperate coniferous and broadleaved mixed forest is an important component of the global forest ecosystem. Therefore, we aimed to investigate the influence of overyielding, stand structure, species asynchrony and dominant species stability on the community stability of a temperate natural coniferous and broadleaved mixed forest and to clarify its main influence mechanism.

Methods In this study, species richness, coefficient of variation of diameter at breast height (DBH), species asynchrony, and dominant species stability were used as independent variables, and community biomass stability, mean biomass and standard deviation of biomass were set as dependent variables, respectively. In this case, three structural equation models were constructed to quantify the relative size of the direct and indirect effects among all variables.

Important findings (1) The structural equation model provides a good fit for the data and accounts for 40.6% of the community biomass stability changes. (2) Species richness was significantly negatively correlated with mean biomass and standard deviation of biomass, with the path coefficients -0.103 and -0.061, respectively. (3) The coefficient of variation of DBH was significantly negatively correlated with the community biomass stability and mean biomass, and the path coefficients were -0.123 and -0.097, respectively. (4) Species asynchrony was significantly positively correlated with the community biomass stability, mean biomass and standard deviation of biomass, and the path coefficients were 0.055, 0.085 and 0.055, respectively. (5) Dominant species stability was significantly positively correlated with the community biomass stability and mean biomass, with the path coefficients 0.623 and 0.085, respectively. And it has a significant negative correlation with the standard deviation of biomass, with the path coefficient -0.68. The results showed that although species asynchrony and stand structure both have significant effects on the community's biomass stability in the temperate coniferous and broadleaved mixed forest, but the dominant species stability is the main factor that directly affects the community biomass stability.

Aims We aimed to examine how changes in vegetation cover and phenology affect the trend of gross primary productivity (GPP) in an Artemisia ordosica shrubland in the Mau Us Desert during the first two decades of the 21th century.

Methods We used the vegetation photosynthesis model (VPM) in combination with remote sensing data (MODIS) to simulate GPP dynamics during 2005-2018. Eddy covariance (EC) measurements of GPP (GPP_Flux) were used to parameterize and validate the VPM model. The “derivation and threshold” approach was used to determine the start (SOS) and the end of the growing season (EOS), as well as the length of the growing season (LOS) for each year. Ordinary least squares (OLS) regression was used to examine the variations in temperature, normalized differences vegetation index (NDVI), and GPP over time. OLS, multiple, and partial correlation analyses were used to test the relationships among temperature, NDVI, phenology, and GPP.

Important findings (1) Modeled GPP well captured the dynamics of GPP_Flux, whereas the MODIS product (MOD17A2H) significantly underestimated GPP_Flux. (2) NDVI, annual maximum NDVI(NDVI_max), and annual GPP all showed an increasing trend during 2005-2018, indicating the role of vegetation recovery in promoting GPP. (3) SOS showed an advancing trend (2.1 d·a^-1) and EOS showed a delaying trend (1.5 d·a^-1), and therefore both SOS and EOS contributed to the increasing trend of LOS (3.6 d·a^-1). (4) Annual GPP was higher with greater LOS (6.44 g C·m^-2·a^-1 for 1 day increase in LOS). (5) Increases in vegetation cover and growing season length explained 79% and 57% of the variations in GPP, respectively. (6) Increases in vegetation cover played a more important role than growing season extension in promoting GPP.

Aims Soil nitrogen (N) mineralization is the main process of N transformation, which determines soil N supply capacity. According to the report that the intensity and frequency of extreme hydrological events such as drought would continue to increase in the future. However, how drought impact on soil N mineralization in tropical lowland rain forests, and if this process is regulated by phosphorus (P) are less understood, given that tropical ecosystem is normally considered as P-limited. Methods Here, we employed a two-factor climate change manipulative experiment (50% throughfall reduction and P addition), which was established in 2019 in a tropical lowland rain forest in the Ganza Ridge Nature Reserve in Sanya, Hainan. The in-situ resin core method was used to study the effects of drought and P addition on soil inorganic N and N mineralization process. Important findings Our results show that: 1) Rainfall reduction significantly reduced the soil moisture at depths of 5 cm and 15 cm, but had no significant effect on soil temperature. 2) Rainfall reduction and the interactive treatment of rainfall reduction and P addition did not impact on soil inorganic N (including ammonium N and nitrate N) content in the dry season or wet season, but P addition significantly reduced soil nitrate N in the dry season, indicated that the effect of P addition on N availability was mainly reflected in the dry season rather than wet season. 3) Rainfall reduction significantly reduced the net ammonification rate and net N mineralization rate in both dry and wet seasons, however, these processes did not respond to P addition or their interaction. 4) Soil moisture positively correlated with the soil net ammonification rate and the net N mineralization rate. Meanwhile, rainfall reduction significantly affected the relationship between the soil net ammonification rate and the ammonium N content, where when the ammonium N was comparable, the net ammonification rate dropped faster under the impact of drought. This indicated that the change of soil moisture was the main factor that affected the soil N mineralization of the study plots. Collectively, our results demonstrated that precipitation changes had an important impact on soil N mineralization in tropical lowland rain forests, but short-term P addition had no significant effect, rainfall reduction and P addition had no interactive effect on the soil N mineralization processes.

Aims The relationships between temporal changes in vegetation growth and climate change tend to be asymmetric. Considering the temporal effects of climate factors on vegetation growth can provide important scientific basis for accurately understanding vegetation-climate relationships and predicting the dynamic responses of vegetation to global climate change. Methods Based on the MODIS normalized difference vegetation index (NDVI), climate, and vegetation type data, this study investigated the temporal effects of climate factors on vegetation growth and the dominant factors influencing vegetation growth on the Qingzang Plateau through establishing four temporal effects equations between climate and vegetation NDVI. Important findings Among the four temporal effects, models considering both time lag and accumulation effects had the highest explanation degree (47%). Compared with model without considering temporal effect, the explanation power of the time lag and accumulation effects on vegetation would increase by 4%-18%. Vegetation dynamics on more than 43% of the Qingzang Plateau was dominated by the combined effects of time lag and accumulation, followed by the area only affected by time accumulation or lag effects, and the area without time effect. The partial correlation coefficient between NDVI and precipitation (0.25 ± 0.56) was overall higher than it between NDVI and temperature (0.08 ± 0.6). The areas dominated by the precipitation were mainly distributed on the northeast and southwest of the Qingzang Plateau with an area ratio of 40.1%, whereas the areas dominated by temperature were largely distributed on the center and southeast of the Qingzang Plateau with an area ratio of 29.7%. These research results can provide basic judgments for the relationships between vegetation growth and climate on the Qingzang Plateau.

Aims Plant phenology is an important indicator of ecosystem response to climate change, and it is also a central parameter for modelling plant productivity and vegetation dynamics. However, it remains unclear whether inner-annual, intra-annual, inter-species or inter-habitat variabilities exist in the response of plant phenology to environmental changes.
Methods Here we investigated the effects of long-term (>10 years) warming and nitrogen (N) addition on plant phenology in a temperate desert steppe. We used the phenological scoring observation method and Richards growth curve fitting method to monitor phenological shifts of three dominant species, Stipa breviflora, Artemisia frigida and Kochia prostrata, in the 11th, 12th and 13th treatment year.
Important findings We found that the flowering time ranged from the 129th to the 145th days of a year for S. breviflora, from the 230th to the 248th days for A. frigida, and from the 194th to the 222th days for K. prostrata. Warming and N addition tended to advance the flowering time of S. breviflora and K. prostrata, but tended to delay the flowering time of A. frigida. The fruiting time ranged from the 134th to the 148th days for S. breviflora, from the 241th to the 260th days for A. frigida, and from the 207th to the 231th days for K. prostrata. Warming and N addition tended to advance the fruiting time of S. breviflora and K. prostrata, but tended to delay that of A. frigida. The reproductive growth period lasted for 12 to 25 days for S. breviflora, 48 to 55 days for A. frigida, and 45 to 77 days for K. prostrata. Warming and N addition shortened the reproductive growth period for S. breviflora, but prolonged that period for A. frigida and K. prostrata.