Aims Nitrogen is the main component of protein and the essential nutrient for plant growth. Soil nitrogen deficiency is a common phenomenon in terrestrial ecosystems. Nitrogen-fixing plants can transfer biologically fixed nitrogen to non-nitrogen-fixing plants in mixed plantation community, which is one of the essential ways for non-nitrogen-fixing plants to obtain nitrogen. This nitrogen transfer is helpful to the restoration of degraded ecosystems, the construction of a stable community and the enhancement of ecosystem productivity. It is essential to identify the effects of environmental and biological factors on nitrogen transfer between nitrogen-fixing and non-nitrogen-fixing plants. Methods To realize this aim, we analyzed 118 pairs of data about nitrogen transfer proportion (ratio of nitrogen transfer to nitrogen content of non nitrogen-fixing plants, P_transfer) using linear mixed model. These data were from experiments on 21 nitrogen-fixing plants and 23 non-nitrogen-fixing plants. Important findings The result showed that soil pH dominated the variation of P_transfer (accounting for 44.04%), followed by mean annual temperature (accounting for 9.14%) and biomass ratio of nitrogen-fixing to non-nitrogen-fixing plants (accounting for 2.95%). As a random factor, the plant species difference accounted for 16.52% variation of P_transfer. In addition, P_transfer in alkaline soil was significantly higher than that in acidic soil. In acidic soil, the mean annual temperature (accounting for 12.49%) and soil total nitrogen content (accounting for 11.72%) were the main factors affecting P_transfer. P_transfer also increased significantly with the increase of mean annual temperature and soil total nitrogen content. In alkaline soil, the variation of P_transfer was mainly influenced by the biomass ratio of nitrogen-fixing to non-nitrogen-fixing plants (accounting for 13.29%), mean annual precipitation (accounting for 10.73%) and soil total nitrogen content (accounting for 9.33%). The biomass ratio of nitrogen- fixing to non-nitrogen-fixing plants and P_transfer were significantly higher in alkaline soil than in acidic soil. Meanwhile, significantly positive correlation was observed between P_transfer in alkaline soil and mean annual precipitation and soil total nitrogen content. These results are meaningful to improve nitrogen transfer between nitrogen- fixing and non-nitrogen-fixing plants, to effectively alleviate the limitation of soil nitrogen on the growth of non-nitrogen-fixing plants and to build a stable plant community.

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

Aims Soil nematodes are good indicator organisms and considered to be one of the important driving forces for the succession of plant communities. Therefore, understanding the relationship between soil nematodes and aboveground communities is particularly important. Methods This study took the soil nematodes in four different types of alpine plant communities, Kobresia humilis meadow, Kobresia tibetica swamp meadow, Carex atrofusca swamp meadow, Potentilla fruticosa shrubland as the research objects in Haibei, Qinghai, China. Nematode community composition, distribution characteristics, species diversity and trophic group composition were studied for the different plant communities. Important findings (1) A total of 3 800 nematodes were extracted with 30 genus, 15 families, 5 orders and 2 phyla. The average individual density of the nematodes was 580 ind.·100 g^-1 dry soil. The number of nematodes decreased with the increase of soil depth. The majority of them were observed in the top soil layer. Different nematode communities vary dramatically among different plant communities. The total number of soil nematodes in K. humilis meadow (1 811 ind.·392.5 cm^-3) was significantly higher than ones from other plant community types. C. atrofusca swamp meadow (324 ind.·392.5 cm^-3) was the least. The composition of dominant genera and trophic groups of soil nematodes saw a significant difference in four plant communities, which is particularly obvious between K. humilis meadow and C. atrofusca swamp meadow. (2) The soil nematode Shannon index (H′) and evenness index (J′) are highest in the P. fruticosa shrubland, and lowest in the C. atrofusca swamp meadow. However, the dominance index (λ) showed opposite patterns. H′ and λ had significant differences between the two plant communities. Potentilla fruticosa shrubland soil nematode community has the highest diversity. Carex atrofusca swamp meadow soil nematode community was lower than those in the other plant meadows, and the nematode community tends to be simplified. The four plant communities rely on the bacterial decomposition pathways. Wasilewska index (WI) of C. atrofusca swamp meadow is the highest and K. humilis meadow is the lowest. It indicates that the state of soil fertility is constantly decreasing in transition from alpine swamp meadow to alpine shrub and alpine meadow. Swamp meadow is beneficial to the growth of microbial nematodes. Plant parasite index (PPI) and maturity index (MI) indexes were the lowest of C. atrofusca swamp meadow. It shows that the maturity of its ecosystem is low. This is related to the higher soil water content in the C. atrofusca swamp meadow. Enrichment index (EI) and structure index (SI) of different plant communities are both the highest in C. atrofusca swamp meadow. It can be seen that the food web of C. atrofusca swamp meadow is relatively connected, with less resistance, and a longer food chain. (3) Principal component analysis (PCA) shows that the four plant communities have different main contribution species. Correlation analysis showed that: bacterivorous nematodes number have a significant positive correlation with K. tibetica swamp meadow; P. fruticosa shrubland has a significant negative correlation with nematode H′, J′, and a significant positive correlation with λ; WI has a significant positive correlation with the plant diversity of K. humilis meadow, while PPI has a significant negative correlation. In summary, plant communities have a profound impact on the diversity of soil nematode communities.

Aims The purpose of this study is to clarify the distribution pattern and the dominant climatic factors of Paphiopedilum Subgen. Brachypetalum in China. Methods Seven species of Subgen. Brachypetalum were investigated as the research objects. The climatic data of 194 geographical distribution points were extracted by ArcGIS. Descriptive statistics were used to analyze the climatic characteristics of the distribution area of the Subgen. Brachypetalum in China, and stepwise regression to fit the linear relationship between climatic factors and their latitude and longitude. Finally, redundancy analysis (RDA) and Monte Carlo-test were used to quantify the contribution of each climatic factor to the geographical distribution of the Subgen. Brachypetalum. Important findings 1) The Subgen. Brachypetalum plants are mainly distributed in southeastern Yunnan, southwestern Guizhou, south Guizhou, northeastern Guizhou, northwestern Yunnan, the junction of northern Guangxi and southern Guizhou, and from northwestern Guangxi to southwestern Guangxi. 2) The monthly mean diurnal temperature range, range of annual temperature, mean temperature of the warmest quarter, mean temperature of the coldest quarter in these distribution areas are 8.13, 23.70, 23.62 and 9.23 °C, respectively. The precipitation variation coefficient, precipitation of the wettest quarter, precipitation of the driest quarter and aridity index are 75.66%, 673.10 mm, 73.97 mm and 26.12%, respectively. As a whole, it has the characteristics of hot and humid climate. There were significant differences in climatic factors between species with narrow distribution and other widely distributed species. 3) Stepwise regression analysis showed that each fitting equation reached extremely significant level. Monthly mean diurnal temperature range, mean temperature of the warmest quarter, mean temperature of the coldest quarter, precipitation variation coefficient, precipitation of the driest quarter, aridity index are the main factors affecting the distribution of Subgen. Brachypetalum along longitude in China. Mean temperature of the coldest quarter, precipitation of the wettest quarter, range of annual temperature, precipitation of the driest quarter, precipitation variation coefficient are the main factors affecting the distribution of Subgen. Brachypetalum along latitude in China. 4) According to the results of RDA analysis, the interpretation rate of climatic factors in the first axis was 73.32%, the interpretation rate in the second axis was 21.29%, and the cumulative interpretation rate was 94.61%. The order of the interpretation rate of climatic factors was: monthly mean diurnal temperature range (57.8%) > mean temperature of the warmest quarter (41.5%) > range of annual temperature (38.3%) > precipitation of the driest quarter (23.1%) > mean temperature of the coldest quarter (16.9%) > precipitation variation coefficient (13.7%) = precipitation of the wettest quarter (13.7%) > aridity index (3.0%). Therefore, monthly mean diurnal temperature range, mean temperature of the wettest quarter and range of annual temperature are the dominant climatic factors affecting the distribution of Subgen. Brachypetalum in China.

Aims We address the issue of adapting patch pattern for improved plant biodiversity conservation in sandy grasslands by assessing the role of edge type in the influences of patch pattern on plant diversity and functional traits. We test the hypotheses that plant richness, alpha and beta diversity would vary according to patch pattern but that these effects would vary according to edge type, through adaptation of plant functional traits. Methods Jointing satellite imagery interpretation, 705 plots from two-year surveys and spatial analysis, patch edges in center Hunshandak Sandland were categorized into four types. Duncan’s differences were tested across four edge types. Pearson’s correlation and redundancy analysis (RDA) were used to discern the patch contributions. Important findings Plant richness and diversity indices are closely related with patch patterns, these relations vary significantly across edge types, demonstrating different functional traits. For inward edge, edge metrics attributes to richness reduction and C₄ plant proportion, mean perimeter-area ratio (MPAR) positively related to nitrogen-fixed species proportion. For outward edge, mean patch fractal dimension (MPFD) negatively related to richness, MPAR positively related to the proportion of nitrogen-fixing species, edge metrics positively related to C₄ proportion. For inward nucleating edge, MPAR, total edge (TE) and landscape area (TLA) positively related to perennial plants, TE and TLA positively linked to insect-pollination plants. For outward nucleating edge, angle and pattern metrics positively related to Shannon-Wiener and Simpson index, negatively related to Pielou index, richness and animal-seed dispersing plants. Patch pattern distressing plant diversity through edge effects can be moderately interpreted by plant practical qualities and edge metrics. It must be well thought-out in landscape management, vegetation restoration and biodiversity conservation.

Aims The study aims to find the relationship between root interspecific interactions and root morphological characteristics, plant height and ground diameter accumulations. The effects of different division methods for the root interaction and interspecific interaction dynamics of chestnut (Castanea mollissima)/tea (Camellia sinensis) agroforestry systems were investigated, in order to provide the scientific basis for the sustainable development in chestnut/tea agroforestry systems. Methods The potting experiment set three cropping system, chestnut/tea agroforestry system, monocropping chestnut and monocropping tea as research objects, and three division methods with solid, mesh, and without root barrier under chestnut and tea roots. Plant height and ground diameter data were fitted to logistic growth models to investigate the temporal dynamics of plant growth, and the allometric relationship between plant height and ground diameter of chestnut and tea were fitted to power function. The relationships between plant growth and root interspecific interaction were analyzed in terms of the fine roots developments. Important findings The results showed that the aboveground dry mass, belowground dry mass, total plant dry mass, root length, root surface area, root volume, fractal abundance and root length of fine roots (0.2-1.0 mm) of intercropped tea with plastic separation were significantly increased by 357.1%, 281.8%, 345.2%, 74.3%, 273.9%, 244.8%, 42.0% and 382.4%, respectively, compared with those of the corresponding sole tea. The asymptotic value of plant height of the intercropped tea with plastic separation was 30.9% higher than the monoculture tea. The asymptotic value of plant height and ground diameter of the chestnut with nylon separation was 21.9% and 28.2% higher than the monoculture chestnut, respectively. In the division methods with plastic, intercropped tea significantly postponed the timing to reach the maximum daily plant height growth rates about 14 days, and intercropped chestnut markedly postponed the timing to reach the maximum daily ground diameter growth rates about 15 days compared with corresponding monocultures. There was significantly positive relationship between plant height and ground diameter of both chestnut and tea in the different treatments. In addition, the slopes of the growth equations about both intercropped chestnut and tea without separation were flatter than the other treatments, which were both lower than 1. Therefore, when tea is intercropped with chestnut trees, chestnut tree shading enhanced the growth of lateral root branches, fine root length and plant height, and facilitated the intercropped tea seedling dry mass accumulation. However, with the growing stresses of underground interspecific competition for intercropped chestnut, the aboveground interspecific facilitation was overridden gradually by the interspecific underground competition, and the final net outcome was manifested as neutral effects.

Aims Based on the background of increasing drought frequency and intensity globally, investigating the photosynthetic properties and growth adaptation of annual grasses differed in photosynthetic pathway (C₃ and C₄) in response to drought-rehydration conditions is useful to predict the changes of grassland ecosystem composition, structure and function in the context of global climate change. Methods The study was conducted as a pot experiment with four annual C₃ and three C₄ grasses widely grown in the Songnen Grassland. Three water levels were set up including control, moderate drought and severe drought. Plant photosynthetic (leaf gas exchange) and growth (biomass, leaf mass per area etc.) parameters were measured at the end of the drought and during the rehydration periods. Important findings The net photosynthetic rate (A) and stomatal conductance (G_s) of all studied species showed a decreasing trend and water use efficiency showed an increasing trend under the drought conditions. There were functional group differences in the effects of drought on photosynthetic properties of the studied plants. The effects of the severe drought on net photosynthetic rate of the C₄ plants are more pronounced than that of the C₃ plants, with the C₄ plants gradually losing their photosynthetic advantage as drought severity increases. The A of the C₄ plants recovered more slowly than that of the C₃ plants after the rehydration because of carbon assimilation in the C₃ plants was mainly restricted by stomata limitation while it in the C₄ plants was mainly restricted by metabolic limitation. The biomass of all studied species decreased, but the root to shoot ratio and leaf mass per area increased, under the drought conditions. The effects of drought on all growth indicators were greater in the C₃ plants than in the C₄ plants. After the rehydration, the biomass of C₃ plants showed a decreasing trend with increasing drought intensity, while the biomass of C₄ plants was not significantly different from the control treatment.

Aims Differences in number of ramets or biomass ratio might have remarkable effects on the adaptability of plant clonal systems to resource heterogeneity. Connected-ramets of bamboo, with lignified rhizomes, usually grow in heterogeneous light environment, but little is known about the response of photosynthetic physiological characteristics in the ramet leaves to heterogeneous light environment and the effects of ramet ratio. Methods The clonal system with four-connected ramets of Indocalamus decorus was grown in the two different shading rates (50% ± 5% and 75% ± 5%) and in the three levels of ramet ratios (the ratios of shaded to unshaded ramets are 1:3, 2:2 and 3:1, respectively). The light response characteristics, gas exchange parameters and photosynthetic pigment content of shaded and unshaded ramets under heterogeneous light conditions were measured at 30, 90 and 150 days after shading treatment, respectively. Important findings The ramet ratio, and its interaction with shading and treatment time had significant effects on photosynthetic physiology of I. decorus. With the increase in the proportion of shaded ramets, leaves apparent quantum efficiency (AQE), light saturation point, maximum net photosynthetic rate (P_{n max}), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and water use efficiency increased, but light compensation point and dark respiration rate decreased, indicating higher photosynthetic efficiency and light utilization of shaded ramets, whereas the reverse was true for connected unshaded ramets. Furthermore, leaves chlorophyll a and chlorophyll b contents of the shaded ramets firstly increased and then decreased, while both the carotenoid content of shaded ramet and photosynthetic pigment (chlorophyll a, chlorophyll b and carotenoid) contents of the unshaded ramets all decreased continuously. Besides, under the same ramet ratio, AQE, P_{n max}, P_n, G_s, C_i and photosynthetic pigments content of leaves in shaded ramets increased with the increment of shading rate, while leaves P_{n max}, C_i and carotenoid contents of the unshaded ramets decreased. Our results indicated that photosynthetic efficiency and light utilization of shaded ramets significantly increased in the heterogeneous light environment, whereas the reverse was true for unshaded ramets. These exhibited obvious division of labor in the clonal system, and ramet ratio of 2:2 and 3:1 showed the better adaptability to heterogeneous light environment than that of 1:3. Therefore, those findings highlighted I. decorus could largely enhance the fitness of the clonal system to adapt to the heterogeneous light environment by modifying the leaf photosynthetic physiology and photosynthetic pigments content, which improved the light utilization and photosynthetic efficiency of the shaded ramets.

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

Aims Juniperus community is an important component of natural forest resources in the Three-River-Source Region, which is significant in maintaining biodiversity and ecological security on the Qingzang Plateau. Yet, the information on the characteristics of the Juniperus community is lacking due to their special geographical location and varied topography. In this study, the main vegetation types of Juniperus community were investigated, and the main characteristics of each community type were described quantitatively by analyzing data from 53 plots. Methods Based on the analysis of forest resources inventory data in the Three-River-Source Region, the representative distribution area of Juniperus was selected to set up 7 sites, a total of 53 plots. Through the investigation of field communities and plot properties, the importance of each species was quantified and calculated. The principle of life form and dominance methods in Vegetation of China were used to determine community types. Important findings (1) The Juniperus plant community in the Three-River-Source Region was divided into 6 alliances, and then further divided into 15 associations. (2) In total, 142 species of seed plants were recorded, which was belonged to 34 families and 90 genera. Among them, Compositae was the major family, accounting for 16.20% of the total species. (3) The vertical structure of the community was obvious, in which the dominant species in the tree layer was single. The dominant species in the shrub layer were Berberis diaphana, Potentilla glabra and shrubby Juniperus tibetica. The herb layer were dominated by Carex and Pedicularis. (4) Among the geographical elements of seed plant species, the Temperate distribution accounted for 52.59% of the total species, while the rest was Chinese endemic species accounting for 47.41%. Temperate Asian, East Asian and Central Asian were the dominated areal-types in the Temperate distribution. Furthermore, the floristic elements of Hengduanshan flora and Tanggut flora were mixed formed the unique characteristic areal-type in the region.