Aims Mechanical abrasion is an important ecological process in the adjacent plant canopy bordering area, which can significantly influence the physiological and morphological characteristics of branches and leaves. However, there is a lack of in-depth research on the characteristics and trade-off mechanisms of the mechanical abrasion on neighboring plant canopies in branches and leaves from the perspective of functional traits.

Methods This study focused on the Tsuga chinensis from the Mao’er Mountain in Guangxi, China. The leaf area, length, and width, as well as the leaf area of the dominant and inferior branches were compared between adjacent canopy layers in mechanical abrasion zones and nonmechanical abrasion zones. Differences in leaf thickness, specific leaf area, leaf dry matter content and leaf dry mass, terminal twig water content, and twig diameter were also analyzed. Moreover, variation and trade-off relationship between branch and leaf functional traits under the influence of mechanical abrasion were evaluated.

Important findings Mechanical abrasion significantly affected the leaf dry matter content, specific leaf area, and leaf dry mass of adjacent canopy leaves. Specifically, the leaf dry matter content of the dominant branches in the mechanical abrasion zone was significantly greater than that in the inferior branches and nonmechanical abrasion zone. Moreover, the specific leaf area of the dominant branches was significantly lower than that of the inferior branches and nonmechanical abrasion areas, whereas the leaf dry mass of the inferior branches was significantly lower than that of the dominant branches and nonmechanical abrasion area. Noteworthy, mechanical abrasion was found to differently influence the relationship between branches and leaves in terms of functional traits. Leaf area- leaf length showed a consistent positive relationship in the mechanical abrasion zone dominant branches, inferior branch, and the nonmechanical abrasion zone. Leaf area-leaf width, leaf area-leaf dry mass, leaf width-leaf thickness, leaf length-leaf width, and leaf thickness-terminal twig diameter were only significantly positively correlated within dominant branches in the mechanical abrasion zone. Leaf area-terminal twig diameter and terminal twig diameter-terminal twig water content were only significantly negatively correlated in the inferior branches. Moreover, leaf dry matter content-leaf thickness was only significantly positively correlated in the inferior branches. Other traits did not show a significant relationship in the dominant branch, inferior branch, and nonmechanical abrasion zone. These results indicate that canopy mechanical abrasion between forest plant neighbors can significantly change the trade-off relationship between branches and leaves regarding to functional traits.

Aims We investigated root-cutting impacts on functional traits of leaves and stems of Leymus chinensis in the vegetative phase in a meadow in Hulun Buir. The aims are to understand the response mechanism of L. chinensis under the disturbance and to provide a references for the restoration of natural mowing grasslands.

Methods A ground intrusive root-cutting machine (9QP-830) was used to cut roots of L. chinensis in May 2014. Since July 2015, we took plants to measure single plant height, leaf length, natural leaf width, spread leaf width, stem diameter, stem length, leaf mass and stem mass at an interval of 15 days until the end of August. Then statistical analysis was applied for the impacts of the treatment on the traits and driving factors to affect phenotypic and qualitative traits of the plant.

Important findings (1) Root-cutting significantly decreased specific leaf area, total leaf mass, stem length/stem diameter, stem dry matter fraction, and significantly increased average leaf length and leaf area. Therefore, it increased individual plant mass, dry matter fraction and height. (2) Dynamics of the traits for both control and treatment followed a quadratic curve. (3) All the phenotypic traits except for the number of leaves in a plant were significantly positively correlated with each other. Leaf mass, stem mass and individual plant mass were significantly positively correlated with each other, whilst specific leaf area was not significantly correlated with the rest of the quantitative traits. (4) Total leaf length and total leaf mass were the greatest driving factors for aboveground biomass among the phenotypic and quantitative traits, respectively. Root-cutting can advance the life history of plant aboveground to some extent.

Aims In this study we constructed and analyzed the standardized chronology of tree-ring width in four coniferous tree species, Abies beshanzuensisvar. ziyuanensis, Fokienia hodginsii, Pinus massoniana and Tsuga chinensis, in southern Luoxiao Mountains, in order to investigate the radial growth characteristics of each species before and after the abrupt change in temperature, and to compare the similarities and differences among the four species in response to climate factors.

Methods Chronologies were developed from the cross-dated ring width series using the program ARSTAN, based on the standardized dendrochronological method. The time trend series of meteorological data from 1960 to 2013 and tree-ring chronologies were analyzed with a linear fitting method. The Mann-Kendall method was used to test the mutation of meteorological data. Growth-climate relationships were determined by calculating the Pearson correlation coefficients between tree-ring width chronologies and climatic factors.

Important findings The tree-ring width chronology of F. hodginsii provided less climatic signals than other three species. The radial growth of T. chinensis was affected by both temperature and precipitation: it was positively correlated with the precipitation in October of the previous year, but negatively with temperature. A. beshanzuensis var. ziyuanensis had a significant positive correlation with precipitation only in August of the previous year. P. massoniana was significantly positively correlated with the mean maximum air temperature in March of the previous year and January of the current year, and significantly negatively with the mean minimum air temperature in July of the previous year and August of the current year. F. hodginsii had a significant positive correlation with precipitation only in March of the current year. When temperature changed abruptly, the pattern of changes in the tree-ring width index was similar among the four species, all with a downward trend. The radial growth response to climate factors was enhanced in all species but A. beshanzuensis var. ziyuanensis, and their growth was inhibited by drought stress following warming. Results from this study provide information concerning the effects of climate change on tree growth and theoretical basis for forest ecosystem management and protection in the southern Luoxiao Mountains.

Aims Litter decomposition plays a vital role in material cycling of ecosystems. However, the responses of litter decomposition to changing precipitation in alpine meadows and the mechanisms underlying these responses are still not clear. Thus this study was designed to address the effect of changing precipitation on litter decomposition of different plant functional groups in alpine meadows.

Methods We used the litter bag method to investigate changes of initial nutrient content, mass loss and nutrient release in the litter of three plant functional groups (grass, sedge and forb) and in communities in an alpine meadow of Eastern Qingzang Plateau, in response to five precipitation treatments, including 90%, 50% and 30% decrease (Pr-90, Pr-50, Pr-30), ambient control (CK) and 50% increase (Pr+50).

Important findings The results showed that: 1) Precipitation decrease (Pr-90, Pr-50, Pr-30) significantly increased the initial nitrogen (N) content, carbon (C):N and lignin:N ratios of grass litters, while precipitation increase (Pr+50) significantly increased the initial phosphorus (P) content of all litter types. 2) According to the Olson negative exponential model, under different precipitation, the forbs decomposed the fastest, with the 95% decomposition time of 3.49-7.45 a; the decomposition of the communities and of the sedge species were the second fastest, with the 95% decomposition time of 4.07-8.05 and 4.65-7.74 a, respectively; grasses decomposed most slowly, 5.84-11.18 a. 3) Extreme precipitation decrease (Pr-90) inhibited the decomposition of all litter types, while moderate precipitation change (Pr-50, Pr-30, Pr+50) inhibited the decomposition of grass litter, but had no significant effects on sedge, forb and community litter, only precipitation increase (Pr+50) promoted the decomposition of forb litter. 4) C release was inhibited under precipitation decrease (Pr-90, Pr-30) in all litter types. N and P release of grass litters were promoted under both precipitation increase and decrease. Pr-30 promoted N release, Pr-90 inhibited P release and Pr+50 promoted P release in sedge, forb and community litters. 5) Structural equation models (SEM) showed that the mass and nutrient remaining rate were directly negatively affected by precipitation, and indirectly affected by litter types through initial C, N, P, lignin, cellulose and hemicellulose content. In conclusion, both litter types and precipitation can affect the mass loss and nutrient release of litters in an alpine meadow. Decomposition was slower and the response to precipitation was more sensitive in grass than that in other litter types. In the future, we should pay attention to the effects of mass loss and nutrient release of grass litter under climate change, especially extreme precipitation decrease, on organic matter input and C, N and P cycling in an alpine meadow.

Aims Leaf stomata are channels for plants to exchange water vapor that affects transpiration and photosynthesis. However, leaf stomatal behaviors are affected by environmental factors and tree species. It is still unclear whether the responses of canopy stomatal conductance to environmental factors differ between tree species and whether the stomatal regulations on canopy transpiration change with different periods of the growing season. The objective of this study was to explore the relative contribution of environmental factors to canopy stomatal conductance and the regulation of leaf stomata on canopy transpiration for different tree species, which could provide references for further understanding the water use status of trees and forest management in mountain areas.

Methods During the growing season of 2018, Pinus tabuliformis (58-year-old) and Acer truncatum (39-year- old) at Badaling National Forest Park in Beijing were selected. Sap flow was measured by using the thermal dissipation method. Environmental factors were also measured synchronously. Canopy stomatal conductance (G_s) was estimated by using the Penman-Monteith equation.

Important findings (1) The daytime G_s of P. tabulaeformis and A. truncatum varied evidently at daily and monthly scales. From May to July, daily dynamic G_s of P. tabulaeformis and A. truncatum increased with vapor pressure deficit (VPD) and solar radiation (GR), in which the rising periods were longer than that during August and September. At the monthly scale, as VPD and GR decreased, soil moisture (VWC) increased, G_s generally increased from May to September. (2) VWC and VPD contributed to the major variation of the G_s, and then the GR, air temperature, and wind speed followed based on the boosted regression tree method. The relative contributions of VWC and VPDto G_s were 66.4% and 17.4% for P. tabulaeformis and 54.8% and 21.0% for A. truncatum, respectively. (3) The slopes between dG_s/dlnVPD and the reference canopy stomatal conductance for both P. tabulaeformis and A. truncatum were significantly larger than 0.6, suggesting that their stomatal regulations were relatively strong. In summary, the response of stomata to environmental factors differs between tree species and different periods of the growing season. Under different soil water conditions, these two tree species could control transpiration through strict stomatal regulation to prevent excessive water loss.

Aims Hainan Island is an area with high species richness of orchids in China. Understanding the impact of environmental variables on the composition and distribution patterns of wild orchids in Hainan Island is critical for the protection and management of wild orchid species and relevant research in the region.

Methods Based on the data of vegetation type, altitude, aspect, slope, mean annual air temperature and precipitation of wild orchids in Hainan Island, this study detected the relationship between species composition and environmental variables by canonical correspondence analysis (CCA), calculated the gross and net effects on species composition for each environmental variable by partial CCA. The effects of different gradients of six environmental variables on the distribution pattern of wild orchids were analyzed.

Important findings The six selected environmental variables explained 3.7% of the variation in the composition of wild orchid plants in Hainan Island. The total and net effects of the six environmental factors including vegetation type, altitude, mean annual air temperature, precipitation, slope aspect, and slope gradient reached a significant level, but their effect intensities decreased successively. The selected six environmental variables all have an impact on the distribution of wild orchids in Hainan Island. Wild orchids in Hainan Island are mainly distributed in areas with the middle altitude, the shady and semi-shady slopes with the slope gradient of 5°-35°, and the environment with low mean annual air temperature and high mean annual precipitation. They are most distributed in native vegetation.

Aims We studied changes in the short-term water use efficiency with environmental factors in typical trees and shrubs of the loess area in West Shanxi. Our objective was to determine the patterns of water use and adaptive strategies in plants of this region, aiming for improving the efficiency of vegetation establishment in the loess area.

Methods Two typical trees, Pinus tabuliformis and Robinia pseudoacacia, and two typical understory shrubs, Rosa xanthina and Periploca sepium, were investigated in this study. Measurements were made on the stable carbon isotope of soluble sugars in leaves (δ¹³C_leaf) and phloem in branches (δ¹³C_branch). δ¹³C_leaf was used to calculated the trend of short-term water use efficiency (WUE_leaf) at the leaf level. δ¹³C_branch was used to determine the carbon fractionation from photosynthesis. We compared the difference in WUE_leaf between species and determined the responses of WUE_leaf to changes in environmental factors.

Important findings From July through to October in the year of investigation, the δ¹³C_leafshowed an overall decreasing trend in the four species, whilst δ¹³C_branch displayed a temporal pattern of “up and down”. δ¹³C_leaf differed among the species and between life forms, in the order of shrubs > trees, and Pinus tabuliformis (an evergreen tree) > Robinia pseudoacacia (a deciduous tree). The WUE_leaf values remained stable from July to August in the four species, and then gradually increased from September to October. Abrupt changes in the WUE_leafvalue occurred at 21.5 °C with temperature (T_a), 0.9 kPa with vapor pressure deficit (VPD), and 52.4% with relative humidity (RH), respectively. Following the abrupt changes, the WUE_leaf value remained steady with further increases in T_a, VPD,and RH in the four species. There were significantly negative correlations between the WUE_leaf value and T_a, RH, and VPD. T_a altered the photosynthetic rate by non-stomatal factors, specifically through the effects on enzymes, causing changes in the WUE_leaf value. The water factor affects transpiration by controlling stomatal opening, and then changes the WUE_leaf value. With increases in soil water content (SWC), the value of WUE_leaf showed a trend of an initial increase and then decreases. The WUE_leaf reached peak value at 15%-18% of SWC in the Pinus tabuliformis stands and 13%-14% in the Robinia pseudoacacia stands. The dominant environmental factors influencing WUE_leaf also differed among species. Linear mixed model (LMM) analysis identified RH as the dominant environmental factor on Pinus tabuliformis, and VPD on Robinia pseudoacacia, respectively; T_a was identified as the dominant environmental factor on both Periploca sepium and Rosa xanthina. This study provides quantitative analysis of water use ability of typical trees and shrubs in the loess area, the internal water consumption mechanism in the growing season, and the major controlling environmental factors, which provides a theoretical basis for the vegetation configuration in this region.

Aims Water transport is of critical impact on the growth of bamboo shoots. The mechanism of diurnal water transpiration by bamboo shoots, and its effect on water transport was not yet fully comprehended. The objectives of this study include: 1) to characterize the structure of bamboo shoots that influence transpiration; 2) to examine the ability of the structure in transporting water; 3) to examine the structure of culm sheath for understanding water transfer in bamboo shoots.

Methods Bambusa emeiensisshoots of different elongation stages were used to characterize the stomata, for examining stomatal conductance (G_s), transpiration rate (T_r) and other physiological features of culm sheaths and shoot body. Water transport rate of shoots in vitro was also examined.

Important findings The results showed that: 1) there are a large number of small and concave stomata on the surface of culm sheath and bamboo shoot of different development states, their net photosynthetic rate (P_n), chlorophyll (Chl) a, and Chl b content were extremely low, but G_s and T_r were significantly higher than that of the mature leaves. These indicated that culm sheath and bamboo shoot play important roles in transpiration and respiration. 2) The tracing results of safranine solution in vitro showed that shoots of higher daily elongation rate had stronger transpiration, and were higher rising rate of safranine solution in the bamboo shoots. When culm sheaths of bamboo shoots were separated, the safranine solution could still diffused and transported in the shoot bodies, indicating that the shoot body itself carried some transpiration. However, compared with the intact bamboo shoots wrapped by culm sheaths, the rising safranine solution decreased significantly after the culm sheaths were separated, indicating that the culm sheath could make important contribution for the water transportation. 3) Anatomical analysis showed that some longitudinal vascular bundles of the internodes formed a plate-like structure (PLS) at the bamboo nodes, and the ends of PLS gradually bent and stretched into the bamboo sheath. The PLS may be an important structural basis for water transport of bamboo sheath.

The karst forests of Junzi Mountain are within the territory of Shizong County in east Yunnan Province, belonging to the vegetation zoning of semi-humid evergreen broadleaf forests and Pinus yunnanensis forests of the mid- and eastern Yunnan Plateaus. These forests are predominantly secondary and typical representatives of the forest remnants in the eastern edge of the zonal vegetation. In order to determine the vegetation types and community characteristics of the karst forests in Junzi Mountain, systematic plot surveys were carried out for species composition, quantitative characteristics and habitat information of all plant communities. Based on analysis of the survey data from 29 plots and the revised vegetation classification system of China, these karst forests could be categorized into 4 vegetation formations, 16 alliances and 27 associations. This paper presents descriptions on the characteristics for each association and provides the original data from all survey plots.