Aims The relationship between biodiversity and ecosystem function is one of the hotspots in ecological research. In the past, the research on the relationship between biodiversity and ecosystem function only focused on the experimental or observational investigation of single ecosystem function (SEF), ignoring the most essential value that ecosystem can provide multiple functions and services at the same time. Identifying the relationship between plant functional diversity and ecosystem multifunctionality (EMF) can provide a clear understanding of changes in ecosystem function.

Methods In this study, Bayanbulak alpine meadow was taken as the study area, and five altitude sites were set at an interval of 200 m from 2 194 to 3 062 m above sea level. Soil total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, total phosphorus content, available phosphorus content, total potassium content, available potassium content, soil density, aboveground and underground biomass of plant community were selected to characterize EMF, which were closely related to nutrient cycling, soil organic carbon accumulation and plant growth.

Important findings (1) The species composition of the plant community varied greatly along the altitude gradient, and the species richness at the altitude of 2 600 m was significantly higher than that at the other altitudes. Functional evenness index (FEve), functional richness index (FRic) and functional dispersion index (FDis) all showed a “single peak” trend with the rise of altitude, and the highest values were found at 2 600, 2 800 and 2 800 m, respectively. Rao’ quadratic entropy (Rao’Q) showed a monotonically decreasing trend. (2) FRic and FDis at each altitude were positively correlated with soil EMF, which accounted for 47% and 43% of the variation in EMF, respectively. FEve was significantly correlated with nutrient cycling index and soil organic carbon storage index at the altitude of 2 600 m. Rao’Q at 3 000 m was significantly correlated with soil nutrient cycling index, organic carbon storage and EMF. The relationship between plant functional diversity and EMF along the altitude gradient was analyzed by constructing a structural equation model, which showed that altitude could exert impacts on EMF through changing functional diversity, with the greatest effect of functional richness on EMF. In conclusion, with the alteration of altitude, the functional diversity may result in changes, thereby affect the SEF and EMF, and the functional diversity is important to maintain the EMF.

Aims To further understand how community functional diversity drives biomass change following nitrogen (N) addition, a nitrogen addition experiment was conducted in an alpine grassland.

Methods Species composition of community and six functional traits of common species were measured in a short-term N addition experiment in Bayanbulak alpine grassland of Tianshan Mountains. We compared the response patterns of species diversity, functional diversity, and community level traits, and quantified the relative contribution of those factors to community biomass variation.

Important findings Both aboveground and belowground biomass increased following short-term N addition, with higher proportional enhancement of aboveground biomass. N addition reduced functional diversity, but did not affect species diversity. At the community level, height and leaf carbon content increased following N addition, whereas specific leaf area, seed mass, and leaf phosphorus content decreased. The variations of species diversity contributed less to the variations of community biomass change, whereas functional diversity and community level traits explained most of the variation of community biomass. Our results support the mass ratio hypothesis. In conclusion, community level functional traits and functional diversity were sensitive to short-term N addition, and played a key role in driving community biomass.

Aims Grassland is an important component of the terrestrial ecosystems in China, and plays a vital role in ecosystem productivity and functioning. During the past decades, 90% of natural grasslands have been degraded as a result of climate change and anthropogenic activities. Grassland degradation altered soil nutrient balance, exerting substantial impacts on ecosystem structure and functions. Our objective was to explore the responses of soil and microbial carbon (C), nitrogen (N) and phosphorus (P) stoichiometry to grassland degradation across the Qingzang Plateau alpine grasslands.

Methods We collected soil samples (0-10 cm) along the degradation sequence (i.e., non-degradation, moderate degradation and heavy degradation) from five sites across the “Three-River Source” region. By determination of soil and microbial C, N and P, we examined the changes in their contents and stoichiometric ratios with grassland degradation. We further synthesized data from the whole Qingzang Plateau alpine grasslands to validate the measured results using a meta-analytical approach.

Important findings Grassland degradation significantly reduced soil organic C, total N and total P contents and their stoichiometric ratios. Although microbial C and N content declined with degradation, change in microbial P content was limited along the degradation gradient. The microbial C:N:P ratios showed minimal responses to degradation. No obvious relationships were observed among soil and microbial C:N:P ratios. The above results indicate that soil microbes have the ability to maintain a given elemental composition despite variation in soil elemental composition following grassland degradation. From a long-term perspective, the nutrient-balance based soil quality promotion technology is able to effectively enhance grassland restoration and improve ecosystem service.

Aims The objectives were to reveal the response patterns of plant species diversity and above-ground biomass to nutrients addition and to clarify their relationships in alpine grasslands of Tianshan Mountains.
Methods The nitrogen (N), phosphorus (P) and potassium (K) addition experiments were conducted in Tianshan alpine grasslands. The single factor effects and the interaction effects on plant species diversity and above-ground biomass were studied from 2019 to 2020.
Important findings 1) Nutrient addition reduced plant species diversity of local community. Especially, the addition of N + P, N + K and N + P + K showed significant effects, suggesting that the decrease of soil niche dimension caused by multiple-nutrient addition was an important reason for local species loss. 2) Nutrient addition significantly increased above-ground biomass of local plant communities, with the highest above-ground biomass being found under N + P + K treatment, indicating that N was the first limiting resource, P and K became the limiting resources after N limiting was alleviated. 3) There was a negative linear regression between species diversity and above-ground biomass following two years of nutrient addition, which indicated that the dominant species but not species diversity determined above-ground biomass at our study site.

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 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 How soil microbial diversity assembly, maintain and change is a key topic of ecology. A large number of studies show that soil microbial biodiversity is controlled not only by soil environment but also by plant species. However, due to strong covariation between the two factors in the field, it remains a challenge to isolate and clarify the role of plant diversity in regulating soil microbial biodiversity. Hence, here, we aim to clarify how plant diversity affects soil microbial diversity in environment-consistent artificial communities.
Methods In this study, we examined differences in species diversity of soil bacteria and fungi among plots subjected single- and mixed-sowing of three grass species with fertilization treatments after 13 years’ experiment on the eastern Qingzang (Tibetan) Plateau. We also analyzed the relationships between soil microbial diversity and edaphic factors as well as plant community attributes.
Important findings (1) The species richness and diversity of soil bacteria, not including soil fungi, significantly and consistently decreased in mixed-sowing plots relative to single-sowing plots, with higher relative abundances in proteobacteria and actinobacteria but lower in acidobacteria, bacteroidetes and planctomycetes in the mixed- sowing plots. (2) Soil pH and total nitrogen content significantly decreased while soil total phosphorus content increased in mixed-sowing plots relative to single-sowing plots. Fertilization significantly increased soil available phosphorus while decreased soil pH and soil humidity. However, variations in these edaphic factors contributed little in variation of soil microbial diversity. (3) Fertilization significantly increased plant aboveground biomass while decreasing richness of present plant species, which was also negatively associated with soil bacterial diversity. In short, this long-term field experiment clearly showed that mixed-sowing of common grass species did not promote diversity of soil microbes. This study provides new insight into management of grasses mixed-sowing artificial grasslands.

Aims The leaf stoichiometry and potential driving factors play a vital role in understanding the distribution patterns of plant community and predicting the plant responses to environmental changes. In this study, we aimed to investigate the spatial distribution patterns and driving factors of leaf carbon (C), nitrogen (N) and phosphorus (P) stoichiometry of coniferous species on the eastern Qinghai-Xizang Plateau, China.
Methods We collected leaf and soil samples from 29 coniferous tree species at 84 sampling sites on the eastern Qinghai-Xizang Plateau. Linear fitting was used to analyze the variation patterns of leaf stoichiometry along geographical and climatic gradients. Partial redundancy analysis was used to characterize the relative contributions of climate and soil factors to leaf stoichiometry variation patterns.
Important findings (1) At the level of family and genus, C and N concentrations as well as C:N of leaves were significantly different across distinct conifer species. The leaf N:P was less than 14, indicating that conifer species in the study region were mainly N-limited. (2) Leaf N and P concentrations showed a consistent distribution pattern along environmental gradients. Specifically, N and P concentrations of leaves were significantly decreased with elevated latitude and altitude, while remarkably increased with the increase of mean annual temperature (MAT) and mean annual precipitation (MAP). In comparison, leaf C concentration had no significant correlation with latitude, altitude, MAT or MAP. (3) The leaf C:N and C:P showed an opposite distribution pattern with leaf N and P concentrations, which significantly increased with elevated latitude and altitude, while markedly declined with the increase of MAT and MAP. Leaf N:P had no significant correlation with altitude, MAT or MAP. (4) The main driving factors of leaf C, N, P concentrations and their stoichiometric characteristics were different. Specifically, soil properties were the main driving factors accounting for the variations of leaf C concentration and N:P. The variations of leaf N and P concentrations as well as ratios of C:N and C:P were primarily explained by climatic factors. Collectively, variations of leaf stoichiometry of coniferous species along environmental gradients in the study region provided a compelling support for the Temperature Biogeochemistry Hypothesis. These findings largely improved the understanding of the distribution patterns and driving mechanism of leaf stoichiometry under changing environments.

Aims Climate change and grazing activities have important effects on species diversity and productivity of grassland ecosystems. The aim of this study is to reveal the differences in responses of species diversity and productivity to warming, grazing and their interactions in an alpine meadow ecosystem. Methods Warming experiment was established in 2011. In 2016, the grazing experiment and the combination of warming and grazing experiment were added. A two-year continuous field experiment was conducted (from 2016 to 2017) and plant community structure, community composition, productivity and species diversity were monitored. Twelve sites were sampled, and were divided into four treatments: control, warming, grazing and the combination of warming and grazing. All sampled species were classified into three functional groups: sedges, grasses and forbs. The species diversity and productivity were sampled in three different treatments. Important findings Results showed that warming and grazing had significant interaction on vegetation height and net primary productivity in alpine grassland. Under grazing treatment, warming had no significant effect on plant height, while warming significantly increased plant height without grazing. Under grazing treatment, the warming effect on net primary productivity significantly differed between 2016 and 2017. In 2016, warming had no significant effect on net primary productivity, while in 2017, warming significantly decreased net primary productivity. Warming and grazing had no significant interaction on species richness, coverage, species important value and species diversity in the alpine meadow. Under the treatments of warming and grazing, the total vegetation coverage decreased, and the proportion of forbs significantly increased. However, no significant effect of warming or grazing was found on species diversity. This study showed that warming and grazing significantly changed the community structure of alpine grassland. Therefore, with the projected climate change in the future, the intensification of grazing activities may lead to the decrease of alpine meadow productivity.

Aims Leaf trait-environment relationships are critical for predicting the effects of climate change on plants. Our objective was to reveal the response of leaf traits of common broad-leaved woody plants to environmental factors on the eastern Qinghai-Xizang Plateau. Methods We measured 15 leaf traits of 332 species from 666 populations collected at 47 sites on the eastern Qinghai-Xizang Plateau. We investigated the extent of leaf trait variation in this area, and explored the response and adaptation strategies of leaf traits to environment at intra- and inter-species levels. Important findings Traits related to leaf size exhibited relatively high variation, and the leaf area was the most variant trait. Most leaf traits were significantly associated with elevation, except stomatal density. Climatic factors were important drivers of leaf trait variation because they explained 3.3%-29.5% of leaf trait variation. Meantime, temperature had the highest interpretation degree of leaf trait variation, and sunshine hours could explain the variation of most leaf traits. However, the interpretation degree of precipitation was relatively weak. In addition, the significant relationships between leaf traits and environmental (altitude and climatic) factors at intra-species level were far less than at inter-species levels. The reason for the result may be the coordinated variation and trade-off between plant traits, which make the variation of intra-species traits relatively small, and thus weaken the correlation between intra-plant leaf traits and environmental factors. Overall, leaf traits were closely related to woody plant adaptation strategies to the environment, and small, thick leaves and short petioles were selected for high-altitude plants to adapt to harsh environments such as strong winds and low temperature.

Aims In this study, we aim to understand how grazing would influence the partitioning of assimilated carbon in an alpine meadow on the Qinghai-Xizang Plateau.
Methods Measurements on carbon partitioning were made in a long-term grazing experiment consisting of light winter grazing and enclosure treatments. The ¹³C tracer method was used to determine the partitioning and transportation of assimilated carbon into different carbon pools.
Important findings On the 30th day following the labeling, shoots retained 32% of the initial ¹³C, and roots and soil together retained 22%; about 30% of the initial ¹³C were lost through shoot respiration. There were significant differences in the retention in soil, and the respiratory emission from soil, of assimilated carbon between the light grazing and enclosure treatments. Under light grazing, plants invested more assimilated carbon into the root and soil carbon pools. The rate of ¹³C transportation from shoots to soil and the rate of respiratory ¹³C release from soil were both greater, and the retention of ¹³C in and respiratory release from shoots were lower, under light grazing than under enclosure. Our results suggest that grazing is an important mechanism for maintenance of grassland. Grazing may cause changes in the structure and functioning of ecosystems, and induce large variations in soil carbon storage. Alpine meadow in the Qinghai-Xizang Plateau is amongst the grasslands with highest elevation in the world, and has large soil carbon storage due to low temperatures. We found no difference in soil C stocks between light grazing and enclosure treatments, indicating that light grazing would have no significant impact on soil carbon stocks.

Aims The study of species diversity patterns is useful in understanding community structure and resource allocation patterns in the succession process in alpine meadows. The present study aims to explore: 1) the changes in community species-abundance relationships in alpine meadows of the Qinghai-Xizang Plateau with mountain slopes; and 2) the difference between the abundances of common and rare species, and their roles in the ecological mechanisms. Methods Field investigation was carried out in alpine meadows of the Qinghai-Xizang Plateau followed by lab analyses in Lanzhou. RAD was used to analyze the difference in environmental factors and plant communities among different slope aspects. Important findings Soil water content increased gradually from the south to north slopes (from 0.18 g·g ^-1 on the south slope to 0.31 g·g ^-1 on the north slope), while soil temperature and light intensity showed the opposite trends (from 22.33 ℃ and 744.15 lx on the south slope to 18.13 ℃ and 681.93 lx on the north slope, respectively). The species abundance and species diversity increased, while the slope of species abundance curves decreased from the south to north slopes. Among the six species abundance fitting models, the ecological niche model best explained the species abundance curves followed by the random distribution model. Further analysis showed that the overall resource allocation pattern of species was mainly fixed distribution. In addition, the resource allocation pattern of the rare species was mainly random, while that of the common species was mainly deterministic.

Aims Root functional traits and their variations mediate coexistence and adaptive strategy of plant species. Yet, strong environmental constraints may induce convergence of root traits among different plant species. To study the variations of root traits and clarify the diverse adaptive strategies across plant species, we sampled three alpine grasslands along a precipitation gradient in the Xizang Plateau.
Methods In three grassland communities along a precipitation gradient: Nagqu, Baingoin and Nyima from east to west of Xizang Plateau, we collected 22 coexisting plant species and measured three key root traits: 1st-order root diameter, 1st-order lateral root length and root branch intensity.
Important findings The main results showed that: (1) the root of plants in the alpine grassland was generally thin, and the interspecific variation was also small (22.76%); (2) the root diameter of 86% plant species was in the range from 0.073 mm to 0.094 mm. Compared with the thick-root species, thin-root species had a higher root branching intensity, but shorter lateral root length. In addition, at community-level, plants mainly increased root diameter and lateral root length, but reduced root branching intensity to adapt to the decreasing precipitation; while at species-level, the plant species exhibited diverse adaptive strategies along the precipitation gradient.

Aims Our aim was to characterize the effects of nitrogen (N) addition on plant root standing crop, production, mortality and turnover in an alpine meadow on the Northwestern plateau of Sichuan Province, China.

Methods A N addition experiment was conducted in an alpine meadow on the Northwestern plateau of Sichuan Province since 2012. Urea was applied at four levels: 0, 10, 20 and 30 g·m ^-2·a ^-1, referred to as CK, N10, N20 and N30. Root samples in surface (0-10 cm) and subsurface layers (10-20 cm) were observed using Minirhizotron from May 10th to Sept. 27th in 2015. The root standing crop, production, mortality and turnover rate were estimated using WinRHZIO Tron MF software. Repeated-measure ANOVA, one-way ANOVA and Pearson correlation were performed to analyze the effect of N addition on soil and root characteristics.

Important findings N addition significantly increased soil available N content and decreased soil pH value, but did not alter soil total N and SOM contents under all treatments. N addition did not exhibit any significant effects on the mean root standing crop and cumulative root production in the 0-10 cm, but significantly reduced mean root standing crop and cumulative root production in 10-20 cm soil layer by 195.3 and 142.3 g·m ^-2 (N10), 235.8 and 212.1 g·m ^-2 (N20) and 198.0 and 204.4 g·m ^-2(N30), respectively. The cumulative root mortality was significantly decreased by 206.1 g·m ^-2in N10 treatment and root turnover rate was significantly increased with 17% for N30 treatment at the 0-10 cm soil depth, but the cumulative root mortality and root turnover rate was not significantly different at 10-20 cm soil depth. In addition, cumulative root production, mortality and turnover rate in 0-10 cm soil layer were significantly correlated with the soil available N content, whereas no significant associations were observed in 10-20 cm soil. Taken together, these results demonstrate that N addition alters the soil N availability and thus induces the root dynamics and changes in root distribution as well as C allocation in alpine meadow.

Aims The alpine meadow degradation could have profound effects on the grassland productivity. The aim of our study is to clarify the dynamic response of community productivity and species diversity in the process of alpine meadow degradation.

Methods In the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Northern Tibetan Grassland Ecosystem Research Station (Nagqu station), we conducted stages experiments with multiple degradation levels: control, mild degraded meadow, moderate degraded meadow, severe degraded meadow and serious sandy meadow.

Important findings The response of aboveground biomass to alpine meadow degradation showed a linear or nonlinear increased response patterns, but the belowground biomass and total biomass decreased nonlinearly. As observed in measurement of aboveground biomass, Margalef index, Simpson index, Shannon-Wiener index and Pielou evenness index also exhibit a nonlinear increased response to degradation. The results of structural equation models showed that belowground biomass has a positive relationship with soil carbon content (p < 0.05) and volume water content (p < 0.1). However, soil nutrient and soil physical properties had no significant impact on aboveground biomass (p < 0.1). Compared with soil physical properties, soil nutrition is an important factor influencing the diversity index. In our study, the nonlinear responses of productivity and diversity of alpine meadow were described by using the multiple levels of degradation in space. The results suggested that aboveground productivity cannot interpret the degree of degradation of alpine meadow, and by contrast, alpine meadow degradation should be measured by the change of plant functional groups, such as edible grasses and poisonous forbs.

Aims The community assembly has been a prominent issue in community ecology. This work was intended to explore the mechanisms of the species coexistence and biodiversity in communities. Our objective was to explore the mechanisms of community assembly in subalpine meadow plant communities along slope gradients in Gannan Tibetan Autonomous Prefecture, Gansu Province, Northwest China.
Methods We selected five slope-oriented plots to construct a super-tree representing the species pool. We surveyed the leaf functional traits and soil environmental factors in different slopes. Then we tested the phylogenetic signal of leaf dry matter content (LDMC), specific leaf area (SLA), leaf nitrogen content (LNC) and leaf phosphorus content (LPC).
Important findings The changes of slope aspect had significant influence on soil water content (SWC) and soil nutrient content. Most of the plants leaf functional traits had significant difference along different slope aspects. The LDMC was higher in south and southwest slope than north slope, while SLA, LNC and LPC were relatively high in north and northwest slope. The LPC showed feeble phylogenetic signal, while LDMC, SLA, LNC did not have a significant phylogenetic signal. With changes in the slope aspect from south to north, community phylogenetic structure shifted from over-dispersion to clustered dispersion. In south and southwest slope, habitat filtering was the driving force for community assembly. Interspecific competition was the main driving factor for community assembly in north and northwest slope aspects. But in west slope, two indices showed contrary consequence. This means the process of community assembly in west slope was more complicated and its phylogenetic index may be the result of several mechanisms working together.

Due to combinations of diverse geography and climate, and complex geo-climate histories and sea level fluctuations, the Sino-Japanese floristic region has extremely high species diversity. Phylogeography is an effective method to identify the factors triggering the formation and differentiation of species diversity. Previous studies showed that phylogeographic breaks, the genetic discontinuity between different gene genealogies, were ubiquitously present. From the west to the east, seven general phylogeographic breaks occur, including the Mekong- Salween Divide, the Tanaka-Kaiyong Line, the Sichuan Basin, ca. 105° E, the boundary between the Second and Third ladders, the North China, and the East China Sea and Korea Strait. These phylogeographic breaks are mainly attributable to both historical and ecological factors, which are generally due to a combined effect of the isolation by distance (IBD) and the isolation by environment (IBE). Geological events and climate changes are the historical factors, mainly including the uplift of Qinghai-Xizang Plateau, the formation and intensification of the Asian monsoon and the Asian interior aridification, the redevelopment of the arid belt, and the Quaternary climate oscillations and sea level fluctuations. Adaptive divergence, namely the divergence induced by different selective pressures under different environments, is responsible for the ecological factors. Adaptive divergence could obstacle gene flow among populations, resulting in the formation of phylogeographic break. However, an identical phylogeographic break is not shared by all the plants because of their various intrinsic biological characteristics, among which the difference in dispersal ability is most important. Finally, we envisaged the future development of phylogeographic break studies based on accurate divergence time estimation, relative contribution of IBD and IBE, and also the utilization of comparative phylogeography.

Aims Shrub recovery is recognized as an important cause of the increase of carbon stocks in China, and yet there are great uncertainties in the carbon sink capacities of shrubs. Our objectives were to estimate carbon density and its spatial distribution in alpine shrubs.
Methods Eight sites in Potentilla fruticosa dominated shrublands across Qinghai, China were investigated. Plant biomass and carbon content in leaves, branches and stems, and roots were measured to analyze the biomass allocation and carbon density.
Important findings Mean carbon densities in biological carbon, litter, soil and whole ecosystem of P. fruticosa shrublands were 5088.54, 542.1, 35903.76 and 41534.4 kg·hm^-2, respectively. Carbon density in the shrub layer was more than 68% of the biological carbon density of the whole ecosystem and was mainly distributed in roots (49.5%-56.1%). Carbon density of the herbaceous layer was 22.5% of the biological carbon density of the whole ecosystem and was also mainly distributed in roots (59.6%-75.1%). The biological carbon density of P. fruticosa shrublands (5.08 t·hm^-2) was lower than the average carbon density of shrub communities in China (10. 88 t·hm^-2). Soil carbon density contributed the largest proportion (85.8%) of total carbon density in P. fruticosa shrublands.

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of carbon input in the terrestrial ecosystem. It is usually limited by nitrogen (N) and phosphorus (P) availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland (NG) and its adjacent restored grassland (RG), to determine the responses of plant community biomass to N and P additions with different land-use. Methods NH₄NO₃ and Ca(H₂PO₄)₂·H₂O were added in a completely randomized block design, with medium levels of 10 g N·m^-2 and 5 g P·m^-2. Soil NO₃^--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO₃^--N and available P contents.Important findings Results showed: (1) N and P additions both increased grass biomass in the NG, and significantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addition; N addition significantly increased both grass and forb biomass in the RG, and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass (p > 0.05). (2) N and P additions both had no effects on the belowground and total biomass in the NG, whereas N addition significantly increased the total biomass by 34% in the RG, which suggested that the effect of N limitation on the vegetation primary productivity was stronger in the RG at present stage. (3) The aboveground biomass in the NG increased with soil NO₃^--N content (p < 0.05), and the above- and below-ground as well as the total biomass were all positively correlated with soil NO₃^--N content in the RG (p < 0.01). These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The “Grain for Green” project (the land-use policy) and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.

AimsStreams are widely distributed in alpine forests, and litter decomposition in which is an important component of material cycling across the forest landscape. The leaching and fragmenting effects as well as the unique environmental factors in streams may have significant impacts on lignin degradation during litter decomposition, but studies on this are lacking.
Methods Using litterbag methods, we investigated the dynamics of lignin mass remaining and concentration (percent litter mass, %) during the decomposition of four foliar litters, which varied significantly in the initial litter chemical traits, from the dominant species of Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana under different habitats (forest floor, stream, and riparian zone) in the upper reaches of the Minjiang River.
Important findings After two year’s incubation, litter lignin mass remaining for a specific litter species varied significantly (p < 0.05) among habitats, with an order of stream < riparian zone < forest floor. Lignin was degraded substantially in the early stage of litter decomposition process, and the lignin concentration first decreased and then increased with the proceeding of litter decomposition, but varied significantly (p < 0.05) among different litter species. Lignin mass showed a general trend of decrease across the 2-year decomposition course. In addition, habitat type, decomposition period and microenvironmental factors (e.g., temperature, pH value and nutrient availability) showed substantial influences on lignin degradation rate. These results suggest that the traditional view that lignin was relatively recalcitrant with an increase of concentration in the early stage of litter decomposition is challenged, but the loss of lignin in the early phrase is in line with recent findings about the fate of lignin during litter decomposition. Moreover, the significant differences of lignin degradation rates among different decomposition period and habitat types indicated that local-scale environmental factors can play a significant role in litter decomposition and lignin degradation processes.

Aims In the cold life zones, snow cover is a comprehensive environmental factor that directly influences soil temperature, soil water content, light and nutrient availability. Plants in these zones develop a series of unique mechanisms involving phenological characteristics, reproductive strategies, physiology and morphology to adapt to environmental changes. This paper is focused on the responses of plant leaf traits, height and biomass partitioning to variations in snow cover thickness, in order to better understand the responses of plant functional traits and specific adaptation strategies under global climate change scenarios. Methods Three transects were established along a gradient of snow cover in an alpine meadow of Mt. Kaka, in the eastern Qinghai-Xizang Plateau. Primula purdomii, Pedicularis kansuensis and Ranunculus tanguticus, which are three widely distributed and dominant ephemerals, were sampled and studied, particularly at their blooming stages. Plant height, specific leaf area (SLA) and biomass partitioning were measured accordingly. Important findings The values of SLA in Pedicularis kansuensis and R. tanguticus were relatively greater under better soil conditions; it was smaller in Primula purdomii with thick snow cover. The relationship between aboveground biomass and belowground biomass in Primula purdomii was allometric at sites with both thick and thin snow cover. No significant relationships were found between aboveground biomass and belowground biomass in Pedicularis kansuensis and R. tanguticus at some individual sites. However, when samples of the three species were pooled, the relationships between aboveground biomass and belowground biomass were allometric at all sites, which did not support isometric scaling hypothesis. In addition, on sites with either thick or thin snow cover, aboveground biomass had greater rate of accumulation than belowground biomass; whereas on sites with medium snow cover, the rate of biomass accumulation was greater for belowground component than aboveground component. Functional traits and biomass variables were better correlated in Primula purdomii and Pedicularis kansuensis than in R. tanguticus.

Strong disturbance and environment stress have significant influence on species diversity (SD) and functional diversity (FD) in plant community. However, the changes in SD, FD and their relationships over time remain controversial. Previous studies showed that the SD-FD relationship along disturbance gradients can represent positive correlation, negative correlation and/or sigmoid curve, respectively. Our aim here is to explore the temporal dynamics patterns of SD and FD in a community experienced disturbance. Particularly, we explored how specific disturbance factor and/or disturbance intensity affect the SD-FD relationship over time.

The experiment was conducted in the alpine Kobresia humilis meadow at Haibei Research Station of the Chinese Academy of Sciences with clipping (unclipping, stubbled 3 cm and 1 cm) and fertilizing (12.75 g·m^-2·a^-1 urea + 3.06 g·m^-2·a^-1 ammonium phosphate) treatments from 2007 to 2013. GLMRMANOVA regression analysis and ANCOVA were used for analyzing the effects of different treatment factors and their interaction on SD, FD, the patterns of temporal dynamics of SD and FD and their relationship over time.

SD and FD significantly increase with increasing clipping intensity. In contrast, fertilization decreased SD and increased feebly FD. During the experiment period, SD declined with time while FD increased. The SD-FD relationship was positively correlated in unclipped and moderate clipped plots, but was not correlated in heavy clipped plots. The slope of SD(x)-FD(y) relationship declined with the increase in clipping intensity. In contrast, fertilization did not change the shape and slope of the SD(x)-FD(y) relationship. The effects of the interaction of clipping and fertilization on SD and FD were not significant, and the slope changes along clipping gradients were identical in fertilized and unfertilized plots. These results suggest that clipping disturbance may induce trait divergence rather than trait convergence in this meadow community, while the strong interspecific competition resulted from fertilizing may not significantly intensify the trait divergence. These findings were inconsistent with the predictions of plant community assembly theory. Compared with fertilizing disturbance, clipping disturbance should play a more important role in shaping the SD-FD relationship.

A plant’s photosynthetic characteristics reflect its adaptive strategies to a given environment. Using pasture plants within enclosures representing communities at different stages of habitat restoration, our objective was to determine how photosynthetic characteristics vary between these different communities and what causes these differences in order to find the theoretical basis to foster rehabilitation of degraded grassland in sub-alpine meadows.

We predicated a succession sequence according to the species richness and the Shannon-Wiener diversity indices, the important values of the main species, and the biotype of five different communities. We measured several photosynthetic parameters including area-based leaf CO₂ assimilation rate (A_area), special leaf area (SLA), foliar nitrogen content based on mass (N_mass), photosynthetic nitrogen-use efficiency (PNUE), water-use efficiency (WUE) and chlorophyll content (SPAD) of dominant species and three common species in each succession stage. Soil water content and total nitrogen of surface soil (0-20 cm) for each community were measured as well. One-way ANOVA was used to find the differences between dominant species, while principal components analysis (PCA) was used to reveal the variation in different communities for each measured parameter.

Photosynthetic traits were different among dominant species and different succession communities. The A_area, WUE and SPAD of the dominant species decreased as succession progressed, but the N_mass, PNUE and SLA showed no consistent patterns related to succession; they varied between different functional groups. For each of the non-dominant species, the A_area and SPAD gradually decreased as succession proceeded from initial stage to climax stage. With succession, WUE and PNUE of the non-leguminous plants (Elymus dahuricus and Geranium wilfordii) decreased while SLA and N_mass increased. However, there were no obvious changes in these parameters for the leguminous plant (Medicago sativa). Soil water content and total nitrogen increased with succession, suggesting that water content and nitrogen are two important factors affecting variation of community photosynthetic characteristics in different stages of restoration succession.

Leaf traits reflect the highly adaptable and self-regulatory capacity of plants to complex environmental conditions. That how they respond to climate change is one of key topics in studies of plant adaptability. This review synthesizes the current understanding on the responses of leaf size, specific leaf mass, leaf nitrogen content and carbon isotopes to climate change. The responses of leaf traits to climate change vary with different leaf structures and ecological properties. Thus, a single leaf trait cannot be used to fully reflect the responses of plants to climate change. There are still a lot of uncertainties concerning the effects of climate change on leaf traits under different scales. Studies are relatively lacking in the alpine region. This review helps us to better understand the relationships between leaf traits and climate as well as the responses and adaptation of plants to climate change. It is critical to predict the variations and evolutionary strategies of plants in response to future climate change.

Log is an important pool of carbon (C) and nutrients in alpine forest ecosystems. Changes in log quality with decay could reveal the process of C and nutrient release during log decomposition. However, little information is available on this. Therefore, this study aims to understand the changes in log quality during log decaying.

Changes in C, nitrogen (N), phosphorus (P), lignin and cellulose concentrations were investigated in the heartwood, sapwood and bark of fir (Abies faxoniana) logs at five (I-V) decay stages in an alpine forest in western Sichuan, China. The stoichiometry of C:N:P and the ratios of lignin:N, lignin:P, cellulose:N, and cellulose:P were also calculated.

C content in bark increased from the stage I to stage III of decay and then significantly decreased, but in the heartwood and sapwood it decreased from the stage I through stage V, especially at stages IV and V. N content increased from the stage I through stage V regardless of the log components. P content in sapwood also showed tended to increase from the stage I through stage V, but P content in heartwood and bark decreased following an increase tendency. In comparison with sapwood and heartwood, bark had the lowest C:N:P stoichiometry at the same decay stages. Percentage of the labile to total C (F_m) also inferred that bark was the most decomposable component. The higher C:N:P stoichiometry in sapwood was observed in logs of the stages I and II, but higher F_m in heartwood was detected from the stage III to stage V. Critical values of C:N in sapwood and bark and C:P in heartwood, sapwood and bark were negatively correlated with the initial N and P concentrations, respectively. Cellulose concentration decreased from the stage I to stage V regardless of log components, and among different components followed the order of heartwood > sapwood > bark at corresponding decay stages. In contrast, lignin concentration increased from the stage I to stage V regardless of log components, and among different components followed the order of bark > sapwood > heartwood at corresponding decay stages. Cellulose degraded faster than lignin regardless of log components, and the ratio of lignin:cellulose increased significantly at the advanced decay stages. Moreover, bark showed a relatively higher lignin:cellulose ratio compared with sapwood and heartwood. In addition, statistical analysis suggested that the degradation of lignin and cellulose in logs would be affected by N concentration. Bark decay was limited by N at early decay stages but by P at all decay stages, and the decay of heartwood and sapwood was limited by both N and P based on ecological stoichiometry theory.

Aims Plant species diversity often declines when nutrients are added in grassland. However, the mechanisms for explaining biodiversity loss due to nutrient enrichment have remained controversial. Our objective was to explore the potential mechanisms of diversity decline.
Methods In this paper, based on a four-year experiment of nutrient addition and grazing in an alpine plant community, we investigate the potential mechanisms of diversity loss by comparing the above- and below-ground competitions using coefficient of variation and nitrogen use efficiency under fertilization scenario both in grazed and non-grazed plots.
Important findings Fertilization increased the size inequality of individuals by 15%, increased species height by different degrees, and reduced the number of species pairs that differed significantly in nitrogen content by 65% in the non-grazed plots. The results indicate that the large-sized individuals out-competed the small-sized individuals due to competition for light, which led to a decline in species richness by 29.6% in the non-grazed plots following fertilization. In contrast, fertilization did not change the size inequality of individuals and species height in the grazed plots, and increased the number of species pairs that differed significantly in nitrogen content by 11.4%, implying that an increased competition for soil nitrogen among species reduced the species richness by 17.3%. Our study also suggests that grazing delayed the effect of fertilization on species richness as inferred by the lower rate of species loss in the grazed plots.

Aims Flower symmetry is closely related to pollination system and variations in flower traits are under the selection role of pollinators. Berg predicted that flower size varies much less in bilateral species than in radial species because of the stable and/or directional selection by pollinators, and that it should also show lower variability than vegetative organs which have relatively higher sensitivity to environments. We examined these so-called Berg’s hypotheses in an alpine meadow.
Methods By measuring the traits of flowers and leaves in 50 flowering plants in an alpine meadow in the eastern Qinghai-Xizang Plateau, we compared the coefficients of variations (CV) in flower size and leaf size between 31 radial and 19 bilateral species and also performed phylogenetically independent comparisons.
Important findings Our results were not completely consistent with the Berg’s hypotheses. The CV of flower size was significantly smaller than that of leaf size in both radial and bilateral species as predicted by Berg, indicating that pollinator-mediated stabilizing selection would benefit flower stability. But the CV of flower size did not differ between the bilateral and the radial species, which is inconsistent with the Berg’s hypothesis even if we controlled confounding effects of phylogenetic relatedness. The role of pollinators in alpine ecosystem where bumble bees and flies predominate is likely more affected by local climatic environments, which leads to considerable variability in the selection of pollinators on flowers.

Aims Shrub recovery is identified as a major cause of an increase in carbon stocks in terrestrial ecosystems in China, and yet there is a great uncertainty in the contribution of shrubs to the carbon sink. Our objectives were to determine the biomass allocation pattern and carbon density in alpine shrubs.
Methods We conducted investigations in 14 shrub communities in eastern Qinghai-Xizang Plateau, at 3500 m above sea level. Plant samples were collected from each plot and measured for biomass in leaves, branches and stems, and roots in laboratory; the data were used to analyze the biomass allocation and carbon density.
Important findings The mean biomass was (5.38 ± 3.30) Mg·hm^-2 in the shrub layer. There were significant differences in biomass between different shrub types, with the mean of (7.28 ± 4.96) Mg·hm^-2 for the broadleaved deciduous shrubs and (4.32 ± 1.36) Mg·hm^-2 for the leathery-leaved shrubs. The indicators of individual feature and community structure were significantly correlated with biomass per unit land area. However, these relationships were developed based on multiple community structure factors; any single factor alone was insufficient to explain the patterns of biomass variations. The patterns of biomass allocation differed significantly between different shrub types. In this study, there was more allocation of photosynthetic products to roots. The mean total community biomass was (6.41 ± 3.86) Mg·hm^-2 and the shrub layer accounted for (83.18 ± 8.14)% of the total community biomass. There were significant correlations (p < 0.05) between shrub layer biomass and herb layer biomass, between shrub layer biomass and litter layer biomass, and between shrub layer biomass and the total community biomass. The biomass of various organs were also significantly correlated (p < 0.01) with the total community biomass. The mean biomass carbon density of the shrubs was estimated at (3.20 ± 1.93) Mg·hm^-2 across the 14 communities by using biomass conversion factor method.

Aims Specific information on geographic distribution of a species is important for its conservation. This study was conducted to determine the potential geographic distribution of Sinopodophyllum hexandrum, which is an endangered plant used in traditional Tibetan medicine, and to predict how climate change would affect its geographic range.
Methods The potential geographic distribution of S. hexandrum under the current conditions in western China was simulated with MaxEnt software based on species presence data at 136 locations and 21 climatic variables. The future distributions of S. hexandrum were also projected for the periods 2020s, 2050s and 2080s under the climate change scenarios of A1B, A2 and B1 described in the Special Report on Emissions Scenarios (SRES) of IPCC (Intergovernmental Panel on Climate Change).
Important findings Results showed that mean temperature of the warmest quarter, annual precipitation, temperature seasonality, and isothermally were the four dominant climatic factors influencing the geographic distribution of Sinopodophyllum hexandrum. For the entire region of the seven provinces in western China, 11.71% of the areas were identified as suitable habitats, 15.86% as marginally suitable habitats, and 72.43% as, unsuitable habitats. The suitable habitats are mainly located in Sichuan, Gansu, Qinghai in the eastern edge of Qinghai-Xizang Plateau, and in areas with rich secondary vegetation and complex terrain in high altitudes. The model simulations indicated that the marginally suitable habitats would have a relatively small change under the climate change scenarios of SRES-A1B, SRES-A2 and SRES-B; whereas the suitable habitats would initially decrease by 2020s, followed by a trend of moderate increased thereafter. The average elevation of suitable habitats would be increased, and both the distributional range and the center of distribution would shift northward first, and then move west to the higher altitudes in mountainous areas of Qinghai-Xizang Plateau.

Aims Rising soil temperature under the warming process stimulates microbial activity in soils on the Qinghai- Xizang Plateau. Moreover, the eastern edge of Qinghai-Xizang Plateau has been experiencing distinct atmospheric nitrogen deposition with an increasing trend. All of these have led to an increase in the available nutrients in soils. This study was aimed to determine the responses of carbon fixation in the alpine meadow to nitrogen and phosphorus additions on the Qinghai-Xizang Plateau.
Methods The study was conducted in an alpine meadow ecosystem at the Haibei National Field Research Station of Alpine Grassland Ecosystem, Northwest Institute of Plateau Biology, Chinese Academy of Sciences. Four treatments were set up in 2009, including control, nitrogen addition only (N), phosphorus addition only (P), and combined nitrogen and phosphorus additions (NP). Nutrients were added in June or July each year. The aboveground biomass of functional groups and the above- and belowground biomass of plant communities were measured by harvesting in 2012.
Important findings (1) N and P additions increased the aboveground biomass of grass, and the proportion of grass biomass in the community, but decreased the proportion of forb biomass in the community. Only P addition decreased the aboveground biomass of sedge, and the proportion of sedge biomass in the community. (2) N and P additions increased the aboveground biomass by 24% and 52%, respectively, compared with the control. (3) N addition had no effect on the belowground biomass, whereas P addition slightly increased the belowground biomass. (4) N addition had no effect on the total biomass, whereas P addition significantly increased the total biomass. Therefore, N and P additions could relieve the nutrient limitation and stimulate plant growth. Furthermore, the results suggest that the Qinghai-Xizang Plateau could be more limited by P than N on plant growth.

Aims Resource-use differentiation among species, which can reduce species competition for the same resources, is the main mechanism to maintain species diversity. Changes in soil temperature and moisture conditions, in the context of global change, may affect nitrogen (N) nutrition of plants of alpine meadow ecosystems. Our objective is to compare the characteristics of N uptake and resource allocation of dominant species of alpine meadow with changes in soil N and water.
Methods An alpine meadow was treated with N and water addition for three years using the method of ¹⁵N isotope injection. We determined the growth responses of dominant species to the N and water additions, as well as the features of N uptake capacity, N allocation and root to shoot ratio.
Important findings The species showed significantly different responses to the N and water treatments, with respect to functional traits of species in N absorption capacity, root N content and root to shoot ratio. There was no significant relationship between N absorption capacity and root N content, whereas N absorption capacity was negatively correlated with root to shoot ratio across all plant species. These results indicated there was ecological niche differentiation in N uptake and a trade-off between the N absorption capacity and resource allocation strategies among species.

Aims Soil fauna has an important effect on litter nutrient release in cold regions, and the effect could vary with litter types and be controlled by environmental factors such as temperature and precipitation. Our objective was to characterize the effect of soil fauna on N and P dynamics during litter decomposition in subalpine and alpine forests.
Methods A field litterbag experiment was conducted in subalpine and alpine forests of western Sichuan, China, from November 2011 through October 2012. Samples of air-dried leaf litter for Salix paraplesia, Sabina saltuaria, Betula albosinensis, and Abies fargesii var. faxoniana were placed in nylon litterbags (20 cm × 20 cm, 10 g per bag) of two different mesh sizes (i.e. 3.00 mm and 0.04 mm). The amount of N and P released were investigated at different stages during the first year of decomposition, i.e., onset of freezing period, deep freezing period, thawing stage, early growing season, mid-growing season, and late growing season.
Important findings The N dynamics during decomposition differed between the leaf litter of broadleaf trees and that of coniferous trees: they were of a release-enrichment-release pattern in Salix paraplesia and B. albosinensis, and of a release-enrichment pattern in Sabina saltuaria and A. fargesii var. faxoniana. The P generally displayed a declining trend, but with an obvious enrichment process in the mid-growing season. During the first year of litter decomposition, soil fauna imposed a positive effect on N release, and a negative effect on P release. There was a significant difference in the amount of litter N and P released through soil fauna among different stages during the first year of decomposition. The amount of N released through soil fauna was positively related to the positive accumulated temperature; whereas the amount of P released through soil fauna was highly negatively related to the positive accumulated temperature. Soil fauna affected more on the litter of broadleaf trees than on the litter of coniferous trees in N and P dynamics during decomposition.

Aims Zelkova, belongs to the Ulmaceae, consists of only six species and has a disjunct distribution in East Asia, West Asia and South Europe. Molecular phylogenetic analysis and dispersal and vicariance analysis (DIVA) were employed to analyze phylogenetic relationships and biogeographic pattern of Zelkova.
Methods The phylogenetic tree was reconstructed based on DNA sequences of trnL-trnF and ITS regions. The analysis of DIVA was used to deduce the biogeographic pattern.
Important findings Results showed that three phylogenetic clades exist in Zelkova, and they correspond to groups from East Asia, West Asia and South Europe. The present phylogenetic tree is different from that in previous study based on nrITS region. DIVA analyses of this genus indicated that the ancestral area of Zelkova was a larger area including East Asia, West Asia and South Europe. The speciation process was dominant by vicariance. Each of the three areas was gradually separated from vicariant events. Based on the high level of species diversity of Zelkova in East Asia, the center of origin is probably the northern Pacific, i.e., north of China and Japan. The current distribution pattern of this genus was likely shaped by historical geological and environmental events, such as the retreat of Tethys, the Qinghai-Xizang Plateau uplift and the Quaternary glaciations that shrank distribution areas.

Aims Under different selection stresses, alpine plants tend to adjust their biomass investments to different functions and/or organs, and this biomass allocation strategy presents different patterns during different life history stages of plants. Our objective is to address three hypotheses regarding Fritillaria unibracteata: 1) elevation gradients impact individual bulb biomass and individual total biomass; 2) biomass allocation adapts to the elevational change of environmental factors; and 3) biomass allocation at different life history stages show different patterns.

Methods We collected wild F. unibracteata at different elevations in the alpine belt of Songpan County in the eastern Tibetan Plateau. The samples were cleaned and divided into different organs, the biomasses of which were then weighed after being dried in the oven.

Important finding Elevation significantly affected individual bulb biomass (IBB) and individual total biomass (ITB), both of which decreased gradually with increased elevation. Elevation representing the heat factor was the pivotal factor limiting the growth of alpine plants such as F. unibracteata. For plants with different life history stages, their biomass allocation presented diverse patterns. First, the bulb biomass allocation (BBA) of 2-year-old F. unibracteata significantly decreased with increased elevation, but its leaf biomass allocation (LBA) increased. Second, both BBA and LBA of 3- and 4-year-old F. unibracteata were relatively stable at different elevations, but their stem biomass allocation (SBA) significantly decreased with increased elevation. In contrast, the sexual reproductive (flower) allocation (SRA) significantly increased with increased elevation. Third, at different life history stages, the root biomass allocation (RBA) of F. unibracteata was relatively stable at different elevations. Both RBA and SBA showed an increasing trend with the growth of plants, but BBA and LBA showed a decreasing trend. Three- year-old individuals normally had the maximum IBB.

Aims The relationship between species diversity and productivity has been a central issue in the face of increasing species extinctions; however, this issue has resulted in many disagreements. Our objectives were to determine (1) forms of the relationships between plant species diversity and productivity in natural communities in subalpine meadow and (2) effect of the sample area on the relationship between plant diversity and productivity. Methods We evaluated the relationships between species diversity and productivity by sampling three different study sites in subalpine meadow in the Hezuo region of Gansu Province, China in 2010. These three sites have different land use histories and altered vegetation traits. Sampling areas in each site were 0.01, 0.04, 0.16 and 0.64 m ². The number of samples was 30 for each site. Sampling at each site was conducted randomly. In August 2010, we determined the aboveground, oven-dried biomass and the number of plant species in each sample quadrat. The relationship between species diversity and productivity was constructed by linearly and quadratically regressing both number of species and aboveground biomass. Important findings We found no significant relationship between number of species and aboveground biomass in two of the three sites, even though sampling areas were varied, and the relationship changed with sampling area in another experimental site that had been overgrazed. Both sampling area and study site had significant effects on number of species, while number of species in each sample increased with sampling area and aboveground biomass per unit area was constant, i.e., sampling areas had no effect on productivity. Variation of experimental site had a significant effect on aboveground biomass, and productivity of each site was not closely dependent on number of species but the site. Results suggest that there may be no fixed relationship between species diversity and productivity in natural communities of subalpine meadow.

Aims Wetlands degradation has drawn increased concern recently. Many researchers have reported the changes of plant communities and the relevant degradation mechanism of wetlands. However, few studies have explored the effects of plant community change on the water conditions of swamp meadow. Our objective was to investigate how change of alpine swamp meadow along degradation gradients affects its water conditions.
Methods The study was conducted at the Research Station of Alpine Meadow and Wetland Ecosystems of Lanzhou University (Maqu Branch Station) (33°39′ N, 101°53′ E). We examined 47 species (15 families) selected from a degradation gradient of alpine swamp meadow. Net photosynthesis rate (P_n), transpiration rate (T_r) and stomatal conductance (G_s) were measured simultaneously with a portable gas exchange system LI-6400 (Li-COR, Lincoln, NE, USA). Measurements were performed from 9:00 am to 12:00 am on clear days in mid-July and mid-August, using photosynthetically active radiation (PAR) = 1 800 μmol·m^-2·s^-1and flow = 750 μmol·s^-1. The value of water use efficiency (WUE) was determined by P_n/T_r. We also investigated the cover of different functional groups (grasses, sedges, legumes and other forbs) at different degradation levels.
Important findings The photosynthetic physiology traits were different among species and functional groups (p < 0.01). The sequence of P_n values of functional groups was grasses > sedges > legumes and other forbs, and WUE was sedges > grasses > legumes and other forbs. Species composition of the plant community had been changed due to the degradation of the swamp meadow. The abundance of forbs increased with degradation. WUE was lower for forbs than other functional groups, which implied that more soil water is transpired, exacerbating the drought condition of degraded meadows. Successful restoration requires protection and replenishment of the typical native species.

Aims Sprouting is an efficient mechanism for forest regeneration to regain lost biomass after disturbances, and it is the main regeneration mechanism of some Quercus forests. Our objective was to study (a) root and sprout growth dynamics of Q. aquifoliodes shrubs after coppicing and (b) the supply of nutrients from the roots and the soil to the new sprouts.

Methods The sites selected were located on Zheduo Mountain of western Sichuan on the south-eastern fringe of the Tibetan Plateau. Post-fire, approximately 30-year Q. aquifoliodes shrubs were cut and sprouts and roots were sampled at 0, 30, 60, 90, 120, 150 and 180 days after coppicing. The roots were separated into fine roots (< 2.5 mm), medium roots (2.5-5.0 mm), coarse roots (> 5.0 mm), and taproot. Root biomass was investigated by excavating whole root systems and sprout biomass by harvesting. The concentrations of nutrient elements were determined by conventional methods. Nutrient supply to sprouts from the root and the soil was calculated based on change in nutrient content of the roots with time and accumulation of nutrients in the sprouts.

Important findings The mean aboveground and belowground biomass of Q. aquifoliodes shrubs was (11.25 ± 0.92) and (34.85 ± 2.02) t·hm^-2, respectively, giving a dry weight root: shoot ratio of 3.10. The biomass of sprouts linearly increased during the course of sprouting. Maximum biomasses of living fine and medium roots occurred in summer. No significant variation was observed for the stump and taproot biomasses. N and P concentrations in fine and medium roots increased in the first 60 days after harvesting; however, the stump, coarse roots and taproot decreased in N, K and Ca concentration. Of all nutrients, Mg showed the greatest variation in the root system. The root system stored much of the nutrient content. The soil, stump, coarse roots and taproots are the main nutrient sources for the initial growth of sprouts between harvesting and 120 days. All nutrients allocated to the sprouts, excluding K, were supplied by the soil between harvesting and 60 days. K was the nutrient most dependent on root reserves for the initial growth of sprouts. K, followed by Mg and Ca, is the nutrient most dependent on root reserves for sprout growth between 60 and 120 days, and the relative contribution of root to sprout P and Mg was very small in this period. Except for K, the soil is an important nutrient source between 120 and 180 days. The management of Q. aquifoliodes shrubs should focus on the protection of underground root systems.

Aims Competition for different limiting resources among plant species is the main factor that influences plant community composition, diversity and productivity. Our objective was to investigate the effects of different levels of nitrogen addition on species richness and aboveground productivity of alpine meadow of the Qinghai-Tibetan Plateau, China.

Methods We added nitrogen in a completely randomized block design and measured plant aboveground biomass, species composition, vegetation light penetration and soil pH and NO₃^--N content in each plot. Regression and analysis of variance were used to analyze the responses of these measures to different levels of nitrogen addition.

Important findings Nitrogen addition changed the soil physical and chemical properties, enhancing the content of NO₃^--N available resources in the soil, increasing plant cover and reducing vegetation light penetration. With increasing N addition, species richness decreased sharply (p < 0.001). N addition changed aboveground productivity significantly (p < 0.05). With increasing N addition, aboveground productivity increased first then decreased, and grass biomass increased while forb and legume biomasses decreased. There was a significant linear positive relationship between species richness and vegetation light penetration (p < 0.05) and also between aboveground productivity and soil NO₃^--N content (p < 0.05). The relationship between aboveground productivity and species richness was negative. We suggested that the short term effects of nitrogen addition on community composition and aboveground productivity were determined by the changed soil NO₃^--N content.

Aims Leaf N and P stoichiometry has been widely studied at the species level in both aquatic and terrestrial ecosystems, however, it lacks research at the community level. Since the ecological stoichiometric characteristics could play important roles in connecting different levels of ecological studies and former studies mainly focused on the individual level, in this study, we try to figure out the pattern of foliar N and P at the community level of grassland ecosystems in Qinghai-Tibetan Plateau. Additionally, we also try to find out the relationships between community level leaf N, P and site climate factors.

Methods Leaf samples were collected from 47 research sites in Qinghai-Tibetan Plateau at the end of the growing season yearly from 2006 to 2008. We measured the leaf N concentrations by using an elemental analyzer and the leaf P concentration based on a molybdate/stannous chloride method. Climate data of annual mean temperature and annual mean precipitation (65 national standard stations) between 2006 and 2008 were used to interpolate into gridded data with a resolution of 1 km × 1 km through the tchebycheffian spline function.

Important findings Leaf N, P concentrations and N:P ratios at the community level over the southern part of Qinghai-Tibetan Plateau were 23.2 mg·g^-1, 1.7 mg·g^-1 and 13.5, respectively. Significant inter-annual differences were presented in leaf N, P concentrations and N:P ratios. Mean annual temperature was strongly correlated with leaf N, P and N:P ratios. Besides, the correlations between climate factors and leaf N, P, N:P ratios were generally consistent with the previous results found at the global scale. Our results suggest that the high variation in leaf P concentration and its strong correlation with environmental factors reveal that, to some extent, stoichiometric traits at the community level are adaptive to local environmental conditions.

Aims ‘Black soil land’ grassland on the Tibetan Plateau results from degradation of Kobresia alpine meadow and has many weeds and poisonous plants. This disturbed grassland forms in small bottomland patches. There are no studies of community spatial patterns, relationships and scale patterns of adult plants and seedlings are important to explaining the formation of this secondary weed community.

Methods We selected a typical ‘black soil land’ community of about 30 m × 50 m in the headwaters of the Yellow River and used 100 sample plots (50 cm × 50 cm) to investigate number and density of adults and seedlings (determined by pulling) by species. Spatial heterogeneity of the community and the similarity between adult plants and seedlings were analyzed by semi-variance, fractal dimension, spatial correlation spatial autocorrelation, etc.

Important findings Species number of adult plants is highly spatially heterogeneous and plant density homogeneous at large scales. Species number of seedlings is highly spatially heterogeneous at small scales, and its density is highly spatially heterogeneous at large scales. Seedlings have high density in areas of micro-topography and gaps of adult plants, where seedlings grow and establish in empty ecological niches. The ‘black soil land’ community regenerates and recruits in vegetation gaps. The generation of ‘black soil land’ community depends on high density of seedlings of weeds and poisonous plants, and its generation capability is strong. According to our results, the ‘black soil land’ secondary community becomes more stable without interference. We suggest that human management be used to decrease the stability of the ‘black soil land’ weed community and restore alpine meadow.