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.

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

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 Horqin Sandy Land is an important, but highly degraded, agro-pastoral region in the northern China region of Nei Mongol. There have been significant changes in vegetation condition over the past two decades, in response to changes in climate as well as restoration policies. In this study, we characterize the spatial and temporal changes in vegetation in the region over the past twenty years, in order to understand the complex mechanism of vegetation change, and provide a scientific basis for comprehensive management and rational implementation of ecological engineering in the future.

Methods We assessed the correlation between a time series of Normalized Difference Vegetation Index (NDVI) (derived from MODIS) from 2001 to 2020 with 10 key driving factors (including mean annual temperature, mean annual precipitation, slope, soil type, vegetation type, geomorphic type, population density, accumulated afforestation area, livestock density, and crops area) in space on random sampling points, which were generated in ArcGIS software. Geodetector model was used to explore the individual relationships as well as their interactions.

Important findings The results demonstrated that: (1) over the past 20 years, the vegetation coverage of Horqin Sandy Land has been gradually recovering, primarily in the northern, central and southeastern marginal areas of the study area, recovery area accounted for more than 64.91%. (2) Changes in NDVI were primarily explained in Horqin Sandy Land by variation in three factors, soil type, geomorphic type, and mean annual temperature. (3) The interactions between explanatory factors were nonlinearly and mutually enhanced, of these, there was a strong interaction between soil type and other factors. (4) Increases in vegetation cover in Horqin Sandy Land was primarily observed in association with alfisol, hills or small undulating mountains, and annual average temperature ranges 4.68-5.67 °C and so on. Future restoration programs may want to prioritize sites with these conditions.

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

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

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

Aims Leaf is an important organ for forest trees to acquire and utilize survival resources, and its morphological structure reflects the habitat adaptability of trees to a certain extent. Exploring the role of geography and climate of the Nanpan-Hongshui River basin in shaping the needles morphology and microstructure of an important tree species in the region, Pinus yunnanensis var. tenuifolia, has important reference value for understanding the ecological adaptability and resource conservation of this tree species.

Methods Eighteen morphological and microscopic characters of nine wild populations which distributed in Guizhou and Guangxi were measured, and seven geographical and climatic factors of the nine population locations were recorded. The population divergence and environmental associations were analyzed by nested ANOVA, correlation analysis, multivariate statistical analysis (principal component analysis, redundancy analysis, and hierarchical clustering analysis).

Important findings The results showed that, except for the ratio of needle cross-sectional area to central cylinder area (V1), all indicators had different degrees of differentiation among populations (phenotypic differentiation coefficient (V_ST) = 22.32%-51.42%). It implied that the habitat heterogeneity among populations had a significant impact on most indicators. Pearson correlation analysis and multivariate statistical analysis showed that the indicators which related to needle resin canals (resin canals number, resin canals perimeter, resin canals area, etc.) increased with the increase of latitude, altitude, and mean annual precipitation, but decreased with the increase of mean annual temperature; the stomatal indicators (stomatal density, ratio of stomatal density to V1) increased with increasing latitude and longitude, and decreased with increasing relative humidity; the indicators which related to the needle cross-sectional size (needle width, needle thickness, needle cross-sectional area, central cylinder area, etc.) are mainly affected by the distance from the sampling site to the Nanpan-Hongshui River. The closer the distance, the smaller the indicator value is. To sum up, P. yunnanensis var. tenuifolia exhibits a trend of miniaturization of resin canal, which was driven by dry-hot habitat selection that is different from that of the original species Pinus yunnanensis. Its higher stomatal density (and sunken stomata) is conducive to balancing respiration and transpiration dehydration in arid environments. The relatively slender needles may be mainly shaped by the stress effects of foehn and strong canyon winds which caused by the special valley terrain in the region, as well as the growth limiting effects of seasonal warm and dry climate on needles.

Aims Understanding the differences in leaf functional traits and their correlations in ferns at different vertical heights can provide a scientific basis for revealing the resource utilization strategies of large fern fronds.

Methods Individuals of three fern species in a mixed broadleaved-Korean pine (Pinus koraiensis) forest, i.e., Dryopteris crassirhizoma, Athyrium brevifrons and Matteuccia struthiopteris were divided into upper, middle, and lower layers according to the vertical height of leaves. We measured specific leaf area, leaf dry matter content, net photosynthetic rate, instantaneous water use efficiency, leaf nitrogen content and leaf phosphorus content, as well as the light environment and soil factors of each individual plant to reveal the vertical variation patterns and correlations of leaf functional traits.

Important findings (1) Leaf dry matter content of the three fern species increased with the vertical height of the fronds, but specific leaf area showed no variation. The net photosynthetic rate of A. brevifrons and M. struthiopteris showed an increasing trend with the increases of vertical height of fronds, the instantaneous water use efficiency of M. struthiopteris increased and then decreased with the vertical height of the fronds, and leaf nitrogen content gradually decreased; leaf phosphorus content of D. crassirhizoma showed an increase and then decreased trend. (2) There were positive correlations between leaf nitrogen content and specific leaf area, and also between instantaneous water use efficiency and net photosynthetic rate. There were negative correlations between leaf nitrogen content and leaf dry matter content, and between leaf dry matter content and specific leaf area. The correlations among those leaf functional traits did not differ significantly among different vertical heights. (3) Soil available phosphorus content and soil pH were the main factors affecting the variation of leaf functional traits at different vertical heights, with soil available phosphorus content having the highest explanatory degree to the variation of leaf functional traits. Our results indicated that there were vertical differences in leaf functional traits of large ferns in the mixed broadleaved-Korean pine forest, but the rate of change among individual characters was basically constant, the effects of light environment and soil factors on the variation of leaf functional traits differed among vertical heights. This study provided reference for further research on the mechanism of leaf functional traits variation in different vertical heights of ferns in understory.

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

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

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

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 In recent years, the aquatic ecosystem of Caohai Lake, in Guizhou Province in southwest China, has shown a trend of phase shift from macrophyte- to phytoplankton-dominated states, which indicates the weakening ecological functioning of the lake. The chlorophyll a (Chl a) concentration is an important indicator of phytoplankton biomass. It is of great significance to clarify the variation of Chl a concentration in comprehensively understanding the ecological status and developing feasible restoration measures for the Lake.

Methods Surface water samples were collected from the Lake in summers and autumns of 2020-2021 to analyze the variation of Chl a concentration. The generalized additive model (GAM) was applied to explore the relationship between each environmental factor and Chl a concentration.

Important findings The results showed that, the Chl a concentration in surface water of Caohai Lake increased during phase shift, with an average up to (17.96 ± 10.62) μg·L^-1(during the monitoring period in 2021), which was 2.5 times greater than that before the phase shift (during monitoring period in 2020). The comprehensive trophic state of the Lake changed from mesotrophic state to eutrophic state, and the water quality presented an obvious trend of deterioration. Results from the single-factor GAM analysis showed that permanganate index (COD_Mn), total nitrogen (TN) concentration and water temperature (WT) had significant effects on Chl a concentration, which among all investigated environmental factors, account for 26.70%-33.30% of the concentration variation of Chl a, with WT, COD_Mn, TN concentration exhibiting the largest, intermediate, and smallest impact respectively. Based on the present study, it is concluded that COD_Mnand TN concentration were important factors driving the variation of Chl a concentration in Caohai Lake, and WT was an inducing factor. The massive extinction of submerged macrophyte and the significant increase of Chl a concentration indicated that the Lake is in phase shift from macrophyte- to phytoplankton-dominated state. Feasible measures should be developed timely to promote the restoration of submerged macrophyte, and further studies on phase shift mechanisms and restoration measures for the Lake should be carried out.

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