In forest ecosystems, vascular epiphytes in the forest canopy act as buffers against environmental pressures, create important habitats for other organisms, increase the complexity of forest ecosystems, and enhance species diversity and community stability. Vascular epiphytes can create distinct habitat forms and perform unique ecological functions. Based on their morphological functional characteristics, they can be categorized into two groups: collecting plants and ant-nest plants. The former group includes “trash-basket” and “tank-form” plants, while the latter group includes “ant-garden” and “ant-house” plants. The present paper discusses the positive effect of vascular epiphytes on canopy biodiversity through the creation of habitats. It reveals the existence of these microhabitats can increase the complexity of the canopy community structure and food web, thereby promoting community stability. Additionally, we analyze how herbivorous defense and nutrient acquisition promote the evolution of special structures of vascular epiphytes for creating habitats, and the impact of these structures on the evolution of other canopy organisms. Drawing on the current research hotspots in canopy science, this paper explores the role of habitat-constructing vascular epiphytes in the three prominent areas: biological interactions in forest canopies, community succession, and responses to global change. This paper highlights the role of habitat-constructing vascular epiphytes as “umbrella species” with significant conservation value in the face of global change. We suggested to strengthen the research on the evolutionary history and ecological functions of different types of vascular epiphytes, and to explore the biodiversity conservation strategies for tropical and subtropical forests ecosystems in the context of global change.

Aims This study aims to explore a high-precision interpolation method of evapotranspiration based on machine learning to construct high-quality data set of actual evapotranspiration.

Methods Taking the typical alpine marsh wetland on the Qingzang Plateau as the observation station to study evapotranspiration, combined with meteorological factors (net radiation, air temperature, soil heat flux, wind speed, relative humidity, soil volumetric water content), we established a prediction model to construct an actual evapotranspiration data set with a high-precision interpolation method based on combining five methods including multiple linear regression (MLR), decision tree (CART), random forest (RF), support vector regression (SVR) and multi-layer perceptron (MLP).

Important findings 1) The correlation between evapotranspiration and net radiation was the largest in the study area, and soil heat flux was the key factor affecting the evapotranspiration process. 2) The determination coefficients are from 0.58 to 0.83 among five machine learning algorithm models with seven combinations, and the root mean square error ranges from 0.038 to 0.089 mm·30 min^-1. 3) The random forest regression model has the highest determination coefficient, the best model stability and the best interpolation. 4) Interpolated evapotranspiration data had the same diurnal variation trend with net radiation, soil heat flux and ari temperature, but the opposite diurnal variation trend with wind speed and relative humidity. Daily evapotranspiration is mainly concentrated in the growing season, with the daily maximum (8.77 mm) on July 9 and the daily minimum (0.21 mm) on January 30.

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 Biodiversity loss threatens ecosystem functions. Investigating the effect of biodiversity on the ecological stoichiometry of plant nutrients, therefore, can help reveal the mechanisms of the effect of biodiversity on ecosystem functions.

Methods Using a tree species diversity experiment in subtropical China, Cunninghamia lanceolatafrom plots with different tree species richness (1, 4, 8, 16, 32) were selected as focal tree species. The effects of neighborhood species richness (NSR), functional trait dissimilarities between neighborhood tree species and the focal tree, neighborhood competition index (NCI) on foliar nitrogen (N), phosphorus (P) content and N:P of C. lanceolata were investigated.

Important findings (1) The results showed that the dissimilarity in specific root length (SRL_diss) between neighborhood trees and focal trees significantly increased the foliar P content of C. lanceolata, while the dissimilarity in root tissue density (RTD_diss) significantly decreased the foliar N content of C. lanceolata. (2) Neighborhood competition significantly decreased the foliar N content and N:P of C. lanceolata. (3) The interaction effects of NCI and SRL_diss, as well as the interaction between NSR and SRL_diss significantly reduced the foliar P content of C. lanceolata. The result indicates that the positive effect of SRL_diss on the foliar P content of C. lanceolata decreased with increasing NSR, and the positive effect of SRL_diss on the foliar P content of C. lanceolata decreased with increasing NCI. (4) The interaction between NSR and phylogenetic dissimilarity (NP_diss) significantly increased foliar N:P of C. lanceolata, demonstrating that the negative effect of NP_diss on the foliar N:P content of C. lanceolata decreased with increasing NSR. Our results indicated that the foliar P content of C. lanceolata was significantly enhanced by mixing with tree species with different trait dissimilarities, while foliar N content of C. lanceolata was decreased by neighborhood competition. Tree species richness can help mitigate the adverse effects of interspecific competition on C. lanceolata through niche complementation when mixing with species that have greater trait dissimilarity.

Aims The aims are to understand the change rule and response mechanism of Leymus chinensis under the disturbance and to provide a theoretical basis and reference for the research on the response of plant functional traits to environmental changes under interference and the restoration of plant population in natural grassland.

Methods We investigated the impacts of fertilization on functional traits of leaves, stems and the whole plant of L. chinensis in the vegetative phase in a meadow in Hulun Buir. Firstly, a ground intrusive root-cutting machine (9QP-830) was used to cut the roots of the grassland, and then different levels of nitrogen and phosphorus mixed fertilizers were applied. Finally, multiple functional traits including single plant height, leaf length, natural leaf width, unfolded leaf width, stem width, stem length, leaf mass, stem mass and single plant mass were measured by stages during the vegetative growth period of L. chinensis. The dynamic changes of functional traits before and after fertilization were analyzed.

Important findings (1) Fertilization significantly increased the aboveground biomass of L. chinensis in the later vegetative growth stage, increased plant height, leaf length, natural leaf width, unfolded leaf width, leaf area, stem length, stem width and stem mass, and decreased leaf dry matter content and stem dry matter content. (2) Fertilization significantly modified the changing trend of functional traits of L. chinensis during the nutritional period. With the increase of fertilization level, plant height, leaf length, natural leaf width, unfolded leaf width, leaf area, specific leaf area, stem length, stem width and stem mass increased gradually from the first increase and then decrease trend of change into a gradual increase, while leaf dry matter content and stem dry matter content decreased gradually. (3) There was a close relationship between phenotypic traits and mass traits of L. chinensis. Leaf area was positively correlated with aboveground biomass and stem dry matter content, and negatively correlated with leaf dry matter content. (4) Fertilization changed the contribution rate of phenotypic traits to aboveground biomass during vegetative growth period of L. chinensis. After fertilization, the phenotypic weight of L. chinensis changed from “concentration-dispersion-concentration-dispersion-concentration” to “dispersion-concentration-dispersion-concentration-dispersion”. In the process of vegetative growth of L. chinensis, plant height is the most sensitive trait to fertilization, and it is also the main phenotypic driving factor affecting the aboveground biomass.

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

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

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

Aims Taking the population of Amygdalus ledebouriana in Balruk Mountain of Xinjiang as the research object, through the investigation of the natural population of A. ledebouriana in Xinjiang, and to provide a certain theory and research basis for the conservation, management and restoration of A. ledebourianapopulation.

Methods The population of A. ledebouriana was investigated and counted by typical sample method. The static life table of A. ledebourianapopulation was compiled using “space substitution time” and uniform sliding technologies, and thus the dynamic change of the population number was analyzed.

Important findings 1) The number of individuals in the III age class of A. ledebourianapopulation in Xinjiang was the largest, accounting for 19.19% of the total individual number. The number of individual plants in the population increased first and then decreased with the increase of age class. The diameter class structure of the population was “spindle”. The age structure of A. ledebourianapopulation in Xinjiang belongs to the recession type. 2) The survival curve of A. ledebouriana was close to the distribution of Deevey-II, and the death peak of the population appeared in the VIII age class, with a mortality rate of 58%. 3) Dynamic change index (V_pi), dynamic change index under external disturbance (V′_pi) of A. ledebouriana population > 0, but V'_pi was close to 0, and the maximum risk probability in random disturbance (P_max) of the population under external environmental interference was 0.38%, indicating that the growth trend of the population was not obvious when it was randomly disturbed by the outside world. 4) After 2, 3, 4, 5, 6, 7, 8, 9 and 10 age classes in the future, the number of young and middle-aged individuals gradually decreases, and the elderly individuals dominate. The lack of seedlings in young individuals is one of the main reasons for the decline of A. ledebouriana population in Xinjiang. Therefore, in order to ensure the normal regeneration of A. ledebouriana population, it is very important to adopt some valid measures, for example, increase the research in the regeneration of A. ledebouriana seedlings in the future, including properly carrying out artificial tending, and protect the A. ledebouriana population by closing the mountains and raising forests in Xinjiang.

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

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

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

Aims As anisohydric plants lacking vascular tissue, mosses are thought to be influenced on their water movement and photosynthesis mainly by the water status and light of the ambient environment. Do the mosses develop an intrinsic circadian regulation mechanism similar to that of vascular plants as these environmental conditions change with day and night alteration? Understanding its rhythmic response characteristics is of great significance for the conservation and utilization of the mosses.

Methods The Brachythecium thraustum, Hypnum plumaeforme and Mnium lycopodioides were trained to 12 h/12 h light-dark (LD) cycles before transfer to 24 h/0 h constant light. We measured the three mosses’ net photosynthetic rate (P_n) and transpiration rate (T_r) on the constant light and last day of the light-dark cycles. Subsequently, non-structural carbon (NSC) content was measured for Brachythecium thraustum. Finally, we sequenced the Brachythecium thraustum transcriptomes in a time series in constant light conditions.

Important findings We found the significant rhythmic changes in the P_n and T_r of the three mosses when excluding environmental influences such as light and vapor pressure difference (VPD), and rhythmic regulation could explain 23.4% and 30.2% of the diurnal changes in P_n and T_r. Moreover, the rhythmic effect of T_r, which is rarely observed in vascular plants, appeared in all the mosses tested, and the rhythmic responses of P_n and T_r were different among species. The species with the strongest rhythm in this study was Brachythecium thraustum, and it was further analyzed for the rhythmic responses of time-series transcriptome and its NSC content under full light. The results showed that 35.1% of starch and carbohydrate biosynthesis-related genes showed rhythmic expression, which was closely related to NSC content change. In addition, the rhythmic regulation of T_r was associated with the transcript changes of abscisic acid signaling and stomatal regulation. Furthermore, the photosynthesis rhythms were associated with transcript changes of photosynthesis-related protein, like photosynthetic electron transport and carbon sequestration proteins. Although the CCA1/LHY genes, the core feedback loop of the circadian clock, have been lost in the mosses, the core circadian clock function concentrates in the PRRs family. The rhythmic response to carbon sequestration and water consumption is highly conserved.

Aims Understanding and quantifying the variability of drought tolerance and the potential driving mechanism in urban trees are critical to the prediction and management of urban ecosystem stability under global climate change. The objectives of this study were: 1) to identify the branch hydraulic traits of trees at urban sites with different percentages of impervious pavements in Beijing, and 2) to investigate if the drought tolerance of urban trees is adapted to urbanization.

Methods The investigated species in the study was Fraxinus velutina. This species is widely applied to street planting in Beijing. We selected six sites along the north-south axis of the city with different percentages of impervious pavements as represented by normalized difference built-up index (NDBI). The NDBI and monthly surface temperature at each site were obtained by remote sensing. The bench dehydration technique was used to assess site-specific branch vulnerability to drought-induced xylem cavitation. Net photosynthesis rate, stomatal conductance, and maximal efficiency of PSII photochemistry (F_v/F_m) were also measured with a photosynthesis instrument.

Important findings The percentage of impervious pavements was positively correlated with the water potential corresponding to 50% loss of hydraulic conductivity (Ψ₅₀), while Ψ₅₀ was found to correlate with pre-dawn xylem water potential (Ψ_pd) and vapor pressure deficit. A significant trade-off relation was found between specific conductivity and Ψ₅₀, but not between leaf specific conductivityand Ψ₅₀. The embolism repair ability was significantly positively correlated with Ψ_pd. The net photosynthetic rate decreased with the increase in percentage of impervious pavement, whereas the F_v/F_m did not show significant difference among sites. The results suggest that the percentage of impervious pavements is one of the key urban environmental indicators affecting the drought tolerance of urban trees. The hydraulic architecture of F. velutinashowed adaptability to the urban environment in the city. The study not only provides important research data for evaluation of the health, resilience, and stability of the urban ecosystems under the scenarios of rapid urbanization and global climate change, but also a theoretical support for decision-makers to formulate practical and feasible management strategies for street planting in Beijing.

Aims Xylem positive pressure (root pressure) has gained new interests after a long period of underestimation, because it is important to restore tissue moisture, maintain function and interconnection of plant hydraulic system, and it contributes to cell and tissue growth.

Methods In this study, hydroponic Dracaena sanderiana of 60-80 cm in height were used to study the circadian variation of root pressure and its determinants, in order to reveal the role that root pressure plays in the upward transport of water across xylem.

Important findings (1) Positive root pressure of D. sanderiana existed throughout the day, and the maximum value obtained was 103 kPa, with a rhythm of high root pressure at daytime and low at night. (2) Root pressure decreased as water temperature declined, and at 0 °C, root pressure reduced to nearly zero and the circadian rhythm was altered too. (3) Different concentrations of nitrate (KNO₃) addition all increased root pressure, but the circadian rhythm was not altered. (4) Root pressure of stems with tillers was smaller (but still positive) than that of stems without tillers. (5) After completely cutting off the fibrous roots, root pressure quickly decreased to negative. In summary, the positive root pressure of most of the hydroponic D. sanderiana can fully provide the force needed to transport the water upwards to leaves throughout the day, and the force of transpirational pull is not needed. At the same time, the root pressure showed a relatively stable rhythm, that is, high at the day and low at night. Temperature, nitrogen content, tillers and root removing all had significant effects on root pressure.

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

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

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

Aims This study aimed to explore change in soil respiration and its components after mild fire, as well as its influence on forest environmental factors, which could provide a scientific basis for the estimation of the soil carbon emission of coastal sandy plantation under the condition of forest fire disturbance.

Methods We conducted an experiment in the Casuarina equisetifolia plantation burnt area and the control plot to measure the total soil respiration rate (R_S) and heterotrophic respiration rate (R_H) in the coastal areas of southern Fujian from September 2019 to August 2020, using the LI-8100 soil carbon flux automatic measurement system. Meanwhile, the soil temperature at the depth of 10 cm (T₁₀), soil volumetric water content at the depth of 10 cm (W₁₀), and soil physical and chemical properties at the depth of 0-10 cm were measured, in order to explore the effects of mild fire on soil R_S, R_H and abiotic factors.

Important findings There were significant differences in soil respiration rate and its components between the burned area and the control area. Our results showed that the annual average soil R_S and R_H in the burned area were (2.37 ± 0.65) and (2.05 ± 0.63) μmol·m^-2·s^-1, respectively. In contrast, the annual average soil R_S and R_H in the control plot were (2.86 ± 1.08) and (2.51 ± 1.08) μmol·m^-2·s^-1, respectively. Soil respiration rate and its components were significantly correlated with soil temperatures in the two plots, except soil R_H in the control plot, but their relationships with soil moisture did not reach a significant level. There was significant positive correlation of soil respiration rate with dissolved organic carbon content, microbial biomass nitrogen content and dissolved organic nitrogen content, but significant negative correlation with microbial biomass carbon content. Overall, we found that mild burning inhibited soil respiration and its components in C. equisetifolia plantation, indicating that fire disturbance had an important impact on soil respiration and carbon cycle in forest ecosystems.