Aims We tested the neutral theory of biodiversity on subalpine meadows of the eastern Tibetan Plateau that exhibited comparatively complicated species composition. Our objective was to explain the species abundance distribution pattern and the underlying mechanism of biodiversity.
Methods We fit the neutral model to a randomly sampled data set obtained in three different habitats (north-facing slope, level field and south-facing slope) and used three methods to test the fitness of the neutral model to the real community: confidence interval, goodness of fit and diversity index.
Important findings We found no significant difference (p>0.05) between the neutral theory predictions and observed species abundance distributions in the three habitats according to the goodness of fit method. The observed data nearly completely fall into 95% confidence intervals of the neutral model predictions (only one out of 63 species in level field communities and 2 out of 75 species in the north-facing slope communities deviate from the 95% confidence interval). There is no significant difference between the neutral theory predictions and observed species abundance patterns, in which the fit of richness predictions is the best (0.49<p<0.56) and the fitness of evenness predictions is relatively poor. However, for the three different habitats, the fitness of these three indices in north-facing slope communities is perfect and the p-values vary between 0.49 and 0.70, but the fitness in level field communities is poorer (p-value of the Simpson diversity index is less than 0.1). Although the test results of the neutral theory by three different test methods and habitats are somewhat different, we conclude that the neutral model can predict species abundance distribution patterns in the three habitats of subalpine meadow.

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.

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.

We measured aboveground live-biomass density (ABD) in 22 sites along the Tibetan Alpine Vegetation Transects (TAVT) for different vegetation types including forests, shrublands and grasslands. Pattern analysis indicated that ABD of natural vegetation in the mountain areas increased from lower to higher altitudinal zones until the maximum was reached at some optimum elevation level and then declined as the altitude continued to increase. We believe that the altitudinal patterns to some extent reflect the latitudinal differences of maximum biomass in global forests. Regressions of transformed data based on the Weber^,s law revealed that January, July and annual mean temperatures and annual precipitation, singly or in combination, accounted for 28%-53% of the variation in ABD along the TAVT where annual precipitation and its combination with annual mean temperature had the highest relationship to ABD (R2=0.46-0.53, p<0.001). The relationships between ABD and the climatic factors could be expressed as logistic equations with a maximum ABD of 1 500 Mg DW·hm-2. However, the variations in annual precipitation and mean temperatures could not explain the highest ABD in the alpine fir forest in Sergyemla Mountains because ABD distribution patterns of natural vegetation can be limited by additional climatic factors such as solar radiation, wind, moisture and related water/energy balances.

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 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.

Clearcutting, a commonly used forest management practice in eastern Qinghai-Tibetan Plateau, is a major driving force for land use change resulted in the drastic degradation of subalpine forest ecosystems. One of the most serious consequences is causing d

Background and Aims Plant resource allocation strategies are important in determining community structure in variable environments. However, observations of changes in species reproductive allocation under disturbance at the community level are rare. This study addresses the following questions: 1) does fertilization alter patterns of species reproductive allocation in natural plant communities, 2) are there interspecific differences for a fertilization effect, and 3) what is the effect of fertilization on assemblage-level reproductive allocation?

Methods The study was conducted at the Alpine Meadow Ecosystem Field Station of Lanzhou University, Maqu (101°53' E, 35°58' N). The experimental plant communities are typical of alpine meadow of the eastern QingHai-Tibetan Plateau. In mid May of 2002 and 2003, we established a soil nutrient gradient of diammonium phosphate (DAP) in the natural plant communities using a completely randomized design (3 levels of fertilization treatments and 3 repetitions of each level). From June to September, we sampled above-ground parts of 24 plant species at their fruiting stage, randomly selecting 20 individuals at every treatment level. The samples were dried to constant weight for 10 h at 80 ℃, and each individual was dissected into fruits, stems and leaves, which were weighed by Sartorius balances (to the nearest 10^-4 g). Reproductive, stem, and leaf allocations were calculated as the proportion of total biomass. ANOVA was used to test the effect of fertilization on patterns of species reproductive allocation.

Key Results Fertilization significantly affected both the biomass and the biomass allocation of most species. Total biomass, leaf biomass, and stem biomass of most species increased with soil nutrient level, but reproductive biomass remained constant or decreased. Reproductive allocation decreased, stem allocation increased, and leaf allocation was constant in most species. The degree and direction of responses differed among species, indicating the differences of life history. Reproductive allocation at the assemblage-level decreased with fertilization.

Conclusions The study suggests that plant individuals tend to become larger, reproductive allocation decreases, and stem allocation and leaf allocation increase as fertility increases. The effect of fertilization on resource allocation strategies is different among species within the same plant community.

The Helan Mountains (38°10′－39°30′　N and 105°45′－106°45′　E) is situated on the eastern edge of the Alashan Plateau and the western edge of the Yinchuan Plain and extend about 270 km from north to south and about 20－40 km east to west. Its general altitude ranges from 2 000 m to 3 000 m with the highest summit at 3 556 m above sea level and relative elevations are 1 500－2 000 m. The Helan Mountains form an important boundary of climate and vegetation in northwest China: the eastern side of the Helan Mountains belongs to steppe climate and steppe vegetation and desert climate and desert vegetation characterize the west resulting in two different biomes. The mountains are a core area of the Alashan-Ordos biodiversity center that is among the top eight centers of biodiversity in China. It is a rich source of plants for the arid west and is an important pivotal point that connects the floras of the Qinghai-Xizang Plateau, the Mongolian Plateau and North China. Hence, it is very important to study the biodiversity of the Helan Mountains. The diversity and spatial distributional characteristics of plant communities are discussed in this paper. Based on our observations and research over many years, we have classified 11 vegetation types, and 55 formations in the Helan Mountains. The vertical zonation of the vegetation is strongly developed: vegetation belts can be divided into the desert belt (below 1 600 m asl), the steppe belt (1 600-1 900 m asl), the coniferous forest belt (1 900-3 100 m asl), and the alpine shrub or alpine meadow belt in the alpine or sub-alpine zone (>3 100 m asl). There also is a strong differentiation of vegetation on sunny and shady slopes. In the steppe belt of low hillsides, steppe communities inhabit sunny slopes but mesophilous shrub occur on shaded slopes. In the coniferous forest belt in the mid-elevation zone, the community of Picea crassifolia is distributed widely on shaded slopes but open forests of Ulmus glaucescens and Juniperus rigida or other mesophilous shrub occur on the sunny slopes. At 3 000 m and upwards, the vegetation of sunny and shade slopes is similar. The vegetation also is differentiated in an east-west and north-south direction resulting in some unique communities. The climate is warm and dry on the east side of the Helan Mountains and some thermophilic plants such as Zizyphus jujuba var. spinosa and Ostryopsis davidiana are distributed on the eastern side only. On the western side, the climate is cool and wet and there is a greater proportion of forests. The mid-elevation zone is the main body of the Helan Mountains, and the vegetation comprised primarily of forests and mesophilous shrub. The degree of desertification is very distinct in both the north and south segments of the mountains, but the communities are different. In the north, Ammopiptanthus mongolicus, Salsola laricifolia and Tetraena mongolica are dominant whereas Ephedra rhytidosperma, Syringa pinnatifolia var. alashanensis are dominant in the south. Furthermore, there are four endemic communities with Syringa pinnatifolia var. alashanensis, Ephedra rhytidosperma, Leptodermis ordosica and Hippolytia alashanensis in the Helan Mountains.

There has been a rapidly increasing interest in the effects of species richness on ecosystem productivity. In order to search for a general species richness-productivity pattern and find the mechanisms underlying the pattern, ecologists have undertake

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 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.

This work was carried out at the Haibei research station of alpine meadow ecosystem in 1980. Not only the distribution range of the Kobresia humilis alpine meadow on the Qinghai-Xizang plateau is widespread, its quality is also excellent. It occupies a very important place in animal husbandry. We have investigated the allocation of the biomass and energy in Kobresia humilis meadow. We measured the biomass dynamics of above-underground by periodical harvest method, and the plants caloric values at different phenological stages were determined by JR-2800 bomb calorimeter. The result expressed: the biomass seasonal dynamics was obvious in Kobresia humilis meadow, the biomass of above ground varied with water and thermal conditions as well as growing development stages of the plants. The biomass above ground achieved peak value (296.66g/m2) on the 1st of September; Then the biomass gradual decreased until ceased before withering. The biomass of underground was medium durint the reviving period, minimum during flourishing period, maximum during the withering period. This concerned the growing development stages and organic matter transport. The plant’s caloric value in Kobresia humilis was maximum during flourishing period, medium during the withering period, minimum during the reviving period. The caloric values of plant groups: sedges was maximum, grasses medium, forbs minimum. The net primary production in Kobresia humilis meadow was 909.40g/m2·a; among others, aboveground part was 296.66g/m2·a; the underground was 596.67g/m2·a. and litter was 16.16g/m2·a; the solar energy storage of community was different in different growing period; the solar energy storage was maximum before the withering period. The utilization rate of solar energy in Kobresia humilis meadow was 0.295 per cent during the gowing season.

A study was made of the native alpine Polygonum viviparum meadow at the Tianzhu Alpine Grassland Experiment Station of the Gansu Agricultural University, which is approximately 150 km northwest of Lanznou, Gansu Pro vince, China. The results obtained were as follows:

1. The alpine Polygonum viviparum meadow at Tianzhu starts growth around the 20th of May. Although there is no absolute frost-free period in the region, the growing season is still 120 days. In the period of the present study the biomass change aboveground showed a monopeak curve during the growing season and the maximum value was 548.39g/m2 dry matter(DM)or 489.06g/m2. ash-free matter (AFM) and it occurred on the 2 2nd of August, and then it begin to decline. Net primary productivity was 481.05 g/m2. a DM or 430.25 AFM. The maximum absolute growth rate was 5.89 g/m2·d DM and the relative one 0.152 g/g·d DM, taking place from 20 May—20 June, i. e. during the first month after the start of growth.

2. Underground biomass of the meadow was quite heavy, the mean value being 6 kg/m2 DM and the change of which, contrary to that aboveground showed a monovalley curve during the growing season. The minimum value of underground biomass was 4556.87 g/m2 DM or 3901.51 AFM, occurring on 20 July and after that, its maxiumu value of was 5996.88 g/m2 DM or 5181.18 AFM, occurring on 20 September, the difference of them (loss of decomposing and grazing etc. were not calculated) was 1440.04 g/m2·a DM or 1235.99 AFM. The absolute growth rate of live roots was 40.27 g/m2·d DM,occurring in second month after the start of growth.

3. The maximum growth rate aboveground occurred in step with the higher negative growth rate underground during the early growing season.

4, The conversion efficiency for total solar radiation aboveground was 0.155%, which for physiological radiation was 0.316% and for physiological radiation during 0℃—≤0℃ growing period was 0.692. The maximum conversion efficiency for total radiation could reach to 0.57%, occurring in the first month of the growing period.

Based on both species-abundance relationship and species diversity, nature of community structure was analyzed under different grazing intensities in alpine meadows and alpine bushlands. The results show that the relative abundance, which accords with the lognormal distribution, demonstrated regular change with growing intensities. Though the community structure changed, the values of indices (e. g. Simpson′s diversity index, λ, shannon′s diversity index H′, McIntosh′s diversity index Dmc evenness index E and species richness R) that are normally used to descibe the nature of communities of different grazing intensities. All above indicate that the changes in community structure can not be explained perfectly by comparing values of species diversity indices only, This result also confirmed the West′s supposition.

The calorific values and nutrient compositions of 4 parts of the biomass of the Polygonum viviparum in the meadow from June to September or November were determined. The results obtained are as follows,1. The average calorific value of standing crop was 18330 j/g DM (20279 ash-free matter,AFM) and ranged from 17980 to 18763 j/g DM(19751 to 20830 AFM). It was higher than that of the standing dead+litter,live roots or dead roots, while that of dead roots is higher than that of live roots. There was some seasonal fluctuation of the calorific value, the highest value of standing crop being in the seed ripening period (August 22) of the dominant species Polygonum viviparum, the lowest being in the withering period. The values of standing dead +litter decreased significantly (P<0.05) as time went on, with live roots and dead roots showing opposite trends.2. The average nutrient components of standing crop were crude protein 13.52, crude fat 2.00, crude fiber 22.99, nitrogen-free extract 51.88, crude ash 9.61% and calcium 1.627 and phosphorus 0.164. Compared with the other 3 parts, the characteristics of the standing crop were. higher crude protein and phophorus and lower crude fiber and crude ash. There were clear seasonal changes in the nutrient compositions of the 4 parts of the biomass and each was different from the others.3. Considering the topography, and its floristic composition, production, easiness of grazing, palatability, and caloric and nutritious values, the authors regard the alpine Polygonum viviparum a good grass for grazing.

This work has been carried out at the alpine meadow research station of Men-Yuan County, Qinghai. The samples were collected during growing seasons in 1978 and 1980. Caloric values of different plants in alpine meadow were determined by JR-2800 bomb calorimeter. The caloric values of 29 species together with that including seasonal changes of 4 species were determined. Caloric values have been compared not only between various plants of same species but also 4 species at different phenologica phases. Caloric values of alpine meadow plants were higher than average caloric of world terrestrial plants but similar to that of dry meadow plants in Norway and Mt. Washington in America. The average caloric values were 4427.5 cal/g (ash-free, ovendry weight). The seasonal change of caloric values of different plants was different. This is correlated with higher altitude cold climate, ash content, plant phenophase and nutrients. It is found that shrubs have significantly higher caloric values than herbs due to their higher lipid content.

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 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.

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.

Minjiang fir (Abies faxoniana) (MJF) is a dominant tree species of sub-alpine forests on the eastern edge of Qinghai-Tibetan Plateau, and is mainly distributed over the upper reaches of the Minjiang, Dadu and Bailong Rivers. The population structure and spatial pattern of MJF was studied in a naturally occurring stand. In a 100 m×60 m plot, the location of every tree was mapped, and the diameter at breast height (DBH), height and canopy area of each individual recorded. Trees were divided into five size classes: seedlings, height <0.33 m; saplings, height ≥ 0.33 m, and DBH<2.5 cm; small trees, 2.5 cm ≤ DBH<7.5 cm; medium Trees, 7.5 cm ≤ DBH <22.5 cm; and big trees, DBH ≥ 22.5 cm. The spatial pattern of MJF was analyzed using four independent methods: the Morisita index (Iδ), variance to mean ratio (V/m), the congregation index (m*/m) and the spatial point pattern analysis (SPPA) (Ripley's second-order- analysis method). The results revealed that MJF was a stable population with an inverse J-shaped size structure indicating good natural regeneration. Seedlings and saplings were very abundant, with densities of 2 217·hm-2 and 2 683·hm-2, respectively. Irregularities in the size structure histogram reflected past disturbances. The spatial analyses revealed that seedlings, saplings and small trees were clumped at most spatial scales studied which ranged from 1 m to 30 m, whereas the medium-sized trees and big trees were randomly distributed. The intensity of assemblage (IA) varied with scale. The first three methods indicated that IA decreased with increasing scale, but the SPPA method showed that the IA of seedlings, saplings and small trees first increased with increasing scale, and then declined at greater scales. We conclude that the spatial pattern of MJF in this subalpine forest resulted from long-term interactions between the MJF and its natural environment and mechanisms of natural regeneration that vary among species. The four different methods were very similar on the whole in their abilities to discriminate spatial patterns, but SPPA was superior in its ability to detect changes of IA with scale. Thus, we recommend SPPA for analyzing spatial patterns of populations. However, a limitation to using SPPA relates to the complexity of sampling and calculation requised and some refinements in Ripley's second-order-analysis are needed in order to better as it detect gaps.

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 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 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.

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 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 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 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.

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.

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 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.

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.

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 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 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 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 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.

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 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.