Aims Own to their genetic characteristics and long-term adaptation to the understory environment, the saplings of subtropical evergreen broad-leaved forest woody species could shoot twigs and develop new leaves several times a year, in which how they survive in the habitats and ultimately grow to adult trees are vital. The objective of this study was to examine what specific adaptation strategies have woody plants taken in the face of environmental pressure in subtropical evergreen broad-leaved forests, especially the growth priorities of twig elongation, stem thickening and leaf area increasing during the shooting process.
Methods The study site is located in Qingcheng Mountain scenic area, Sichuan Province. We chose five species with high second shooting rate in similar habits. Five plants with no disease and insect pests of each species were randomly selected for tree height measurement and long-term shooting observation. Each plant was randomly labeled with three young current-year twigs from different direction outside of tree canopy, and the twig length, twig diameter, leaf number and area were recorded when the twigs burst. The scaling relationships between traits of twig and leaf were analyzed by standardized major axis estimation (SMA).
Important findings 1) The first and second shootings started from spring (April) and late summer (the late August) respectively. The proportion of the second shooting of trees was lower than that of shrubs, and the proportion of second shooting of evergreen plants was lower than that of deciduous counterparts respectively. 2) The twig length and individual leaf area, the twig diameter and leaf number (expect for the Symplocos grandis) of the first shooting were all higher than those of the second shooting, but the relative growth rate of individual area and leaf mass per area of the first shooting were lower than those of the second shooting. 3) The maximum relative growth rates of the twig length and leaf number, the twig diameter (expect for Eurya loquaiana and Castanopsis carlesii var. spinulosa) and total leaf area (expect for Castanopsis carlesii var. spinulosa) of the first shooting were all higher than those of the second shooting, and appeared in the first and second weeks of shooting. 4) In the two shootings, all the plants put priorities on the growth of leaf area and number, then on the growth of twig length, and finally on the twig diameter. The individual and total leaf area showed a significant allometric scaling relationship with the increasing of twig length and diameter, indicating that the growth rate of leaves was higher than that of twigs. The relationship between the individual leaf area and the leaf number was significantly greater than 1, suggesting that the growth rate of the individual leaf area was higher than that of the leaf number. Besides, the relationship between the twig length and diameter was also significantly greater than 1, suggesting that the growth rate of the twig length was higher than that of twig diameter. The study reveals the shooting strategies formed by plants improved their survival and reproductive ability by obtaining more resources (especially intercept the light resources).

Aims Evergreen (EBL) and deciduous broad-leaved (DBL) woody angiosperms are two major plant groups in the subtropical broad-leaved forests of eastern Asia. Exploring the separation between these two groups in ecological niche, will shed light on the biodiversity maintenance mechanisms of subtropical broad-leaved forests.
Methods Adopting statistical methods including the linear regression model and the multiple regression method of Mantel test, we compared the phylogeny and ecological behaviors of the two plant groups in eight forest dynamics plots in China.
Important findings We found that (1) leaf habit, be either EBL or DBL, was phylogenetically conserved in the 788 study angiosperm taxa. EBLs and DBLs differed in ecological behaviors towards light, temperature, water, soil reaction and soil fertility. EBLs prefer low light and soil pH, high temperature, water and soil fertility; while the opposite was true for DBLs. (2) Within plot, DBLs were more clustered in phylogenetic dispersion, but more overdispersed in ecological behavior, compared with EBLs; similarly, between plots, DBLs were less diverse in phylogenetic composition, but more diverse in ecological behaviors, than EBLs. On the other hand, divergence in phylogenetic composition of DBLs between plots increased with difference in mean annual temperature (MAT). Further, we found that (3) the ratio of DBLs to EBLs in species richness decreased with MAT increased, but not with dry season length or annual precipitation. The findings show that EBLs and DBLs of the eight study plots differ in both phylogeny and ecological behaviors, and imply that niche separation may be a major mechanism that maintains the biodiversity of subtropical broad-leaved forests.

Aims In subtropical forests, topographic heterogeneity drives ecosystem structure and species composition by regulating the available nutrients, water and light needed for tree growth. A gap in current research is the role of topographic heterogeneity in plant species diversity and distribution in monsoon evergreen broad-leaved forests. Our study aims to fill this gap, providing scientific grounds for the conservation of biodiversity through an exploration of floral structure and ecosystem development in monsoon evergreen broad-leaved forests.
Methods Within a 30 hm² dynamics plot, we established 750 20 m × 20 m sample plots, using fuzzy C-mean clustering to classify different topographic types based on elevations, convexities, slopes, and aspects of each sample plots. We compared community composition and community species diversity between different topographic types, using Torus-translation tests to examine the relationship between floral species and topography.
Important findings We identified five distinct topography types: ridge (8.00 hm²), steep slope (6.04 hm²), less-steep slope (7.68 hm²), high plateau (2.76 hm²), and valley (5.52 hm²). We counted a total of 153 418 woody plant individuals with a diameter at breast height (DBH) ≥ 1 cm, belonging to 271 species, 179 genera and 79 families. Among the topographic types, we noted differences in species richness, plant density, proportion of different diameters, species diversity and the abundance of dominant species. When comparing species-area relationships between the five topographic types, we noticed that the ridge had the lowest number of species, while the valley had the highest. The cumulative species-individual relationships within the topographic types revealed that the ridge possesses the lowest cumulative rate. Of the 123 examined species, 67.5% were significantly related to at least one type of topography. Among species significantly related to topography, those species with significant negative correlation were more abundant in the ridge and steep slope topographic types. The opposite was true in steep slope, high plateau and valley. Based on our data, we determined that topographic heterogeneity contributed 7.8% to the maintenance of species diversity in our study area.

Aims The patchy distribution patterns of vegetation result in heterogeneous microhabitats and thus affect seed germination and seedling establishment in arid ecosystems. The impact of changes in microhabitat conditions on the colonization of native plants and the specificity need to be understood for restoring vegetation by adopting microhabitat regulation measures in arid ecosystems where vegetation degradations are exacerbated by climate change and increasing anthropogenic disturbances.
Methods Three types of microhabitat conditions, including vegetation cover of shrubs and semi-shrubs, respectively, and bare lands, were selected in an dry valley in Minjiang River basin. The effects of microhabitat conditions on seedling establishment were studied in Bauhinia brachycarpa by measuring the survival rate and the height and biomass of seedlings. The microhabitat effects on seed germination and seedling establishment were also studied in six other native plant species on an extremely degraded roadside slope.
Important findings The results show that B. brachycarpa seedlings had significantly greater survival rate and total biomass, as well as greater biomass of roots and shoots on bare lands than in habitats with shrub and semi-shrub covers; whereas the specific leaf area and leaf mass fraction of seedlings were smaller on bare lands than in shrub and semi-shrub patches. Humus addition treatment significantly increased the total biomass of seedlings in bare land microhabitat. Moreover, non-woven geotextile cover and humus addition treatment increased the germination rate in herbaceous plants, resulting in high herb density four months after treatment. The results suggest that humus addition and geotextile cover are effective in regulating microhabitat for improvement of seedling colonization and maintenance of the community structure stability. In conclusion, uses of native plants are important in the vegetation restoration of extremely degraded sites in arid regions due to their strong adaptability to road slope habitats and capability of forming a shrub-grass mosaic community structures.

Aims Biomass-partitioning patterns influences the growth and reproduction of individual plant, and the mass and energy flow of a plant community. Revealing the biomass-partitioning patterns of alpine shrubs can help understand their life-cycle strategies and the uncertainty of shrub carbon sink.
Methods In this study, the biomass-partitioning ratio and allometric relations of each organ at individual level were analyzed in seven typical evergreen shrub species in Rhododendron in alpine-subalpine of southern Gansu using whole-plant harvesting method.
Important findings The results showed that the average fractions of biomass allocation in root, stem and leave for seven Rhododendron species were 35.57%, 45.61% and 18.83%, respectively, with significant differences in fractions of biomass allocation of each among species. There were allometric relations and isometric relations between leaves vs stems, leaves vs roots, stems vs roots, and aboveground biomass vs underground biomass for all species. However, allometric scale did not fully support the reference values of metabolic scaling theory and isometric scaling theory of small plants. There were significant allometric relationships in leaf mass, stem mass and root mass among species. The combination of the optimal partitioning theory and allelotropic theory help better understand the biomass variation and adaptation mechanism of Rhododendron species in mountainous areas in southern Gansu.

Aims The nutrient characteristics of nitrogen (N) and phosphorus (P) in plant leaves are affected by soil available N, P contents and soil N:P. However, little is known about the effects of changes in soil N, P contents and N:P on N, P stoichiometry in leaves and nutrient resorption efficiency.
Methods In this study, pot experiments were conducted to explore the response of the stoichiometry and nutrient resorption characteristics of Achnatherum splendens leaves to three levels of nutrient addition (low, 1.5 g·m^-2·a^-1; moderate, 4.5 g·m^-2·a^-1; and high, 13.5 g·m^-2·a^-1) and N:P (5, 15, 25).
Important findings The results showed that higher level of nutrient addition significantly increased the P contents in green leaves and N, P contents in senescent leaves, but significantly deceased the N resorption efficiency (NRE) and P resorption efficiency (PRE). The increases in soil N:P significantly decreased the P contents in senescent leaves and NRE, but increased N:P in green and senescent leaves and PRE. At the same nutrient addition level, soil N:P was significantly positively correlated with PRE, but showed no significant correlation with NRE. At the same level of N:P, the level of nutrition addition was negatively correlated with NRE, but exhibited no significant correlation with PRE. The changes in plant demand for N and P caused by changing environment can be indicated effectively by plant leaf NRE:PRE, and the characteristics of nutrient stoichiometry and resorption of A. splendens leaves are affected together by nutrient addition levels and soil N:P.

Aims Increasing global nitrogen (N) deposition has exerted significant influences on productivity and carbon cycle of terrestrial ecosystems. More than 90% of the carbon in grasslands is stored in the soil, therefore any changes in soil total respiration (R_s) might have a vital impact on the carbon balance and the stability of soil carbon pool of grassland ecosystems. Most of our understanding about the responses of R_s to N deposition was based on N deposition manipulative experiments with short-term (<5 years) and low frequency (1-2 times per year) N addition treatments. It is still unclear how the long term N addition and different N addition frequency will affect R_s and its components in semiarid grasslands.
Methods Our study is based on a long term N addition manipulative experiment platform conducted in a typical temperate semiarid steppe, Nei Mongol. The experimental treatment consisted of six N addition amounts and two N addition frequencies. N addition treatments began at 2008. Soil respiration and its components were measured every two weeks during the growing season in 2018 and 2019.
Important findings 1) R_s significantly decreased with increasing N addition amount. The negative impact of N addition on R_s was mainly resulted from the inhibition of heterotrophic respiration (R_h). 2) No significant differences were observed in responses of R_s and its components to low and high frequency N addition treatments. 3) Soil acidification caused by long term N addition inhibited soil microbial activity and changed soil microbial community composition, consequently decreased R_s and R_h. Our results suggested that the negative effect of N addition on soil carbon release still lasted after a decade of N addition treatment. In particular, the decrease of R_h would enhance the stability of soil carbon pool. No significant differences in the two N addition frequency treatments indicated that the potential impacts caused by simulated N addition with different frequencies would be diminished with prolonged treatment period. Therefore, the results of long-term (>10 years) simulated N addition experiments can provide reliable references for evaluating the responses of natural ecosystems to atmospheric N deposition.

Aims As a discontinuous disturbance factor, forest fire is one of the drivers of biogeochemical cycles. It significantly changes the structure and function, nutrient cycling, and energy transfer of ecosystems and alters the forest carbon pools and carbon distribution patterns, consequently affecting the processes of forest succession and carbon sequestration capacity. This study aims to determine the impacts of incidental forest fire on soil organic carbon density, and to explore the mechanisms of forest fire impacts on soil organic carbon fixation.
Methods The study was conducted in secondary Pinus massoniana forests of different ages in Guangdong Province, using the method of space for time substitution. The sampling plots were set up on adjacent sites of burned and control stands, and soil samples (0-60 cm) were collected from each plot for indoor tests and analysis of the physical and chemical properties. The soil organic carbon components were measured and calculated for density. Changes in soil physical and chemical properties and soil organic carbon with forest ages were quantified.
Important findings Fire reduced the soil organic carbon density in secondary P. massoniana forests; the level of reduction in soil organic carbon density decreased with forest age and soil depth. Compared with the controls, the soil organic carbon density in the burned plots of young, mid-age and mature forests were 10.93%, 8.52% and 7.56% lower, respectively. The soil organic carbon density in the burned plots of young, mid-age and mature forests varied in the range of 5.04-7.76, 5.26-10.27 and 6.33-13.58 t·hm^-2, respectively, along the soil profile of 0-60 cm, which were 2.51%-16.83%, 1.31%-11.85% and 1.09%-12.50% lower, respectively, than the controls. Fire significantly reduced the soil organic carbon density of the young and the mid-age forests in the 0-30 cm soil layer, and of the mature forest in the 0-20 cm soil layer. There were significant correlations between soil organic carbon density and soil physical and chemical properties. Path analysis revealed the greatest direct effect of soil total nitrogen content on soil organic carbon density in both the control and burned plots; fine root biomass had a smaller direct effect, but imposed an indirect effect on soil organic carbon density via its controls on soil total nitrogen content. Nested ANOVA showed that soil depth accounted for 70.60% of the variations in soil organic carbon density, forest age 25.35%, and fire 2.34%.

Stipa sareptana var. krylovii alliance is one of the typical steppes endemic to Central Asia. The eastern border of its distribution is adjacent to the meadow steppes on the Hulunbeir Plateau, the western border extends to the desert steppes on the Ulanqabu Plateau and Tianshan Mountains, and the southern border lies among the warm temperate steppes on the Loess Plateau. The distribution of this alliance also spreads into the alpine steppes on the eastern margin of the Qinghai-Xizang Plateau. The broad its distribution suggests that S. sareptana var. krylovii alliance has wide ecological adaptability. In this study, we described and analyzed the eco-geographical distribution, community characteristics and classification of S. sareptana var. krylovii alliance based on data from 117 plots. The results showed that there are 336 seed plants belonging to 36 families and 131 genera in these plots. The families with more than 15 species are Gramineae, Compositae, Leguminosae, Rosaceae, Chenopodiaceae and Liliaceae. Among all species in these plots, 91.67% are rare species with occurrence frequency smaller than 20%. Besides S. sareptana var. krylovii, the most common species in this alliance include Cleistogenes squarrosa, Heteropappus altaicus, Agropyron cristatum, Koeleria cristata, Potentilla bifurca, Salsola collina, Allium tenuissimum and Leymus chinensis. In addition, hemicryptophytes are the most common life form within the surveyed plots, accounting for 66.37% of all species. Xerophytes are the most common water ecological type, accounting for 61.19% of all species. East Palearctic element was the major floristic geographical element, accounting for 33.33% of all species. Based on the China Vegetation Classification System, S. sareptana var. krylovii alliance could be classified into 6 association groups and further into 45 associations.