Aims The response of plant phenology to climate warming is an important element of global change research. At present, studies on plant phenology response to climate warming are in severe shortage for high-altitude ecosystems, especially regarding responses to multiple-level warming.

Methods We conducted a multiple-level warming experiment in an alpine meadow on Qingzang Plateau, and monitored plant phenology of two dominant species, including the timing of green up, budding and flowering in 2015, 2017, 2018 and 2021.

Important findings The results showed that plant phenology of different species exhibited various trends under warming. For Kobresia pygmaea, delay in phenological development, including green up, budding and flowering, was positively correlated with temperature increases. However, the timing of phenological stages of Potentilla saundersiana showed advancing first, and then delay with increasing temperature. These results suggest that plant phenology of alpine meadow asynchronously responds to increased temperature. In addition, temperature increase exerts delayed effects on plant phenology over long-term. The structural equation modeling showed that temperature increase consistently delayed the green up of K. pygmaea, and low-level warming advanced phenological development of P. saundersiana, but this advancing trend reversed under high-level warming. Importantly, soil moisture plays a key role in determining the magnitude and direction of phenological response to climate warming in our study. Our findings indicate the asynchronous characteristics of plant phenology response to climate warming in alpine meadow ecosystems, and provide basis to predict responses of high-altitude ecosystems to climate change in the future.

Aims Vegetation traits are one of the research hotspots in plant ecology and they reflect the strategies of plant survival. According to the CSR survival strategy model, plant species may be classified into three categories: C strategy that can maximize biomass in resource-rich environments (competitive species); R strategy that can rapidly intake resources and reproduce in environments with a high frequency of disturbance (opportunistic species); and S strategy that can maintain individual survival in resource-poor environments (tolerant species). Leaf traits have adaptive changes in response to environmental gradients, which have impacts on plant adaptation. The mechanisms of how leaf traits affect CSR survival strategies in the alpine grassland of Qingzang Plateau remain unclear. The objective of this paper is to investigate the spatial patterns of CSR survival strategies of alpine plants and the mechanisms by which environmental factors influence plant survival.
Methods We surveyed a field transect which consists of 53 sample sites in an alpine grassland on the Qingzang Plateau from July to August 2020. Vegetation traits of leaf area, leaf fresh mass, and leaf dry mass were measured and C, S, R values were calculated. Finally, we analyzed the critical drivers and mechanism of plant CSR strategies in response to geographical elements.
Important findings Our results showed that: (1) In the alpine grassland of the Qingzang Plateau, 41.6%-96.7% of plants are identified as S strategy. (2) With the increase of the longitude, the proportion of C strategy plants increased gradually from the west to the east, whereas along the altitude gradient, the proportion of C strategy plants decreased with the increasing altitude. (3) Random forest analysis showed that the contribution of precipitation to C strategy is the highest (25.74%), and the contribution of altitude to S strategy is the highest (27.34%). Additionally, both precipitation and temperature had significant effects on leaf area, and leaf water content significantly affects plant CSR strategies. In summary, results of our study highlighted that precipitation is the most critical factor that governs plant CSR survival strategies. This finding has important implications for studying the ecological adaptation along environmental gradients in alpine grasslands.

Aims Seed size and number variation is the core issue in the study of plant fitness. Exploring the grazing effects of different large herbivore assemblage on the relationship between seed size and number of dominant species in Kobresia grasslands, is helpful to understand the reproductive strategy and population regeneration mechanism.

Methods This research was conducted on the technical platform of adaptive management of alpine grassland- livestock system on the Qingzang Plateau. There were six grazing treatments: no grazing (control), single yak grazing, single Xizang sheep grazing, yak:Xizang sheep grazing ratios of 1:2, 1:4 and 1:6. And we analyzed the reproductive characteristics of K. humilis, the relationship between seed size, seed number and its tradeoff.

Important findings The results showed that: 1) Grazing treatment increased the seed size and seed number of K. humilis by more than 15% and 30%, respectively. The variation coefficient of seed size decreased by at least 15% under other grazing treatments except for yak:Xizang grazing ratio of 1:2. While the variation coefficient of seed number decreased by more than 25%. 2) Pearson correlation analysis showed that there were positive correlation between seed size, seed number and reproductive traits under grazing treatments. 3) Grazing treatments increased the tradeoff between seed size and seed number which was largely affected by the mass of single reproductive branch. The results suggest that even at moderate grazing, livestocks are still the limiting factors for the acquisition of resources. Long-term grazing changes the potential relationship and tradeoff among the traits of K. humilis, stabilizes the features of seed size and seed number. The reproductive strategy of K. humilis is optimized by increasing seed size and seed number, which improves the near-ground competitiveness and fitness of offsprings.

Aims Climate change is significantly altering the phenology and growth pattern of alpine plants related to their resource allocation strategies, thereby changing the functioning of alpine ecosystems. The aim of this study is to explore responses of reproductive phenology and vegetative growth of alpine plants to climate warming on the Qingzang Plateau.

Methods Experimental warming was achieved using infrared heating. From 2017 to 2018, we measured the reproductive phenology (leaf out, flower bud, flower and fruit time) and maximum height of 15 common alpine plants (account more than 80% of the total above biomass) under non-competitive condition via common garden experiment.

Important findings Our results showed that: (1) Experimental warming significantly advanced the leaf out, flower bud and first flowering day of legumes by (8.21 ± 1.81), (9.14 ± 2.41) and (10.14 ± 2.05) d, respectively. In addition, warming significantly prolonged the flowering duration of legumes by (6.14 ± 1.52) d. This result implied that different functional groups showed different responses under warming. The reproductive phenology of most alpine plants advanced, and the flowering duration was prolonged under warming, suggesting that more resources was allocated to reproductive growth. (2) In addition, experimental warming significantly reduced the height of forbs by (3.58 ± 0.96) cm, but not of other functional groups. Different species have differential responses to warming in different year. In summary, the alpine plant community on the Qingzang Plateau may start the reproductive stage earlier, hence reducing the resource allocation for vegetative growth under future warming conditions. In addition, due to different responses of the reproductive capacity and vegetative growth of various species to temperature change, climate warming may change the coverage of various species, and then alter the composition of species in the community, and then change the function of alpine ecosystem.

Aims The variations in population structure and the quantitative dynamics of plants are a reflection of the local ecology and environment. Hippophae tibetana is a dwarf shrub, and a pioneer species of vegetation succession which is peculiar to the alpine region of the Qingzang Plateau. It has excellent water and soil conservation effects and good ecological adaptability to high-altitude environments. However, little research has been made into the changes in the population structure and dynamics at different altitudes. Such an understanding is important to understanding the ecological strategy of H. tibetana adaptation to alpine habitats. The Qilian Mountains in the northeastern margin of the Qingzang Plateau contain degraded alpine grassland and are ecologically fragile. It is thought that the irregularly distributed native species, H. tibetana, plays an important role in water conservation at 2 700-3 300 m in this region.

Methods The structure, dynamics, life span and morphological characteristics of H. tibetana populations distributed at three altitudes (2 868, 3 012, and 3 244 m) in Tianzhu Zangzu Autonomous County, Qilian Mountains were studied and quantified, establishing static life tables and population survival curves. This quantitative analysis of the population dynamics was used to try to determine future population development trends.

Important findings We found: 1) The plant height, basal diameter and crown width of H. tibetana decreased with elevation. The age structures of all populations at the three altitudes were roughly spindle-shaped, with abundant mature individuals but few seedlings and few old plants. Populations were found to be stable. 2) The survival curves of all populations tended to approach the Deevey-II type, and the survivability was greatest at low altitude, medium at middle altitude, and lowest at high-altitude. The mortality and disappearance rates were both high, ranking from highest to lowest with high-altitude > low-altitude > middle-altitude. Seedlings were proportionally more abundant at the middle and high altitudes. Life expectancy was greatest at middle-altitude > low-altitude > high-altitude. 3) The dynamic index (V′_pi) of each altitude population was close to 0, indicating that all populations were stable, and the maximum of probability under random disturbance (P_max) of the middle altitude population was the smallest, indicating that the middle-altitude populations were the most resiliant to random interference. The middle altitude was the most suitable for the growth of H. tibetana. 4) The proportion of seedlings in all populations is likely to decrease, while the proportion of mature and old plants will increase over the next 2, 4 and 6 age classes of time. Any decline in the total populations at the three altitudes is likely due to the lack of young individuals, interspecific and intraspecific competition, and environmental stress. These findings will enable us to predict future growth and death of H. tibetana populations and provide a reliable theoretical foundation for the protection of natural forests in this region. This will be important to the future management of these alpine environments as global climate warming makes its impact.

Aims The mountainous region on the east side of the Qingzang Plateau is a biodiversity hotspot and a refuge for many plants during the ice age. The unique topography allows geographic isolation to play an important role in shaping population genetic patterns. The white birch (Betula platyphylla) population located on the eastern side of the Qingzang Plateau shows a fragmented distribution, which is isolated by valleys, mountains, and rivers, and the genetic pattern is still unclear.

Methods We used 11 pairs of nuclear microsatellite molecular markers to analyze the genetic diversity and structure of 13 birch populations located in the eastern mountainous area of the Qingzang Plateau.

Important findings A total of 114 alleles were detected in 412 individuals, and we found a high level of overall genetic diversity (expected heterozygosity (H_E) = 0.579; observed heterozygosity (H_O) = 0.555), a medium level of genetic differentiation (genetic differentiation coefficient (F_st) = 0.127), and a large pairwise genetic distance between groups (F_st = 0.017-0.319). The genetic distance was significantly positively correlated with geographic distance. The cluster analysis divides all individuals into two groups, bounded by the Yalong River Canyon. The population on the west side has lower genetic diversity and greater genetic differentiation than the population on the east side. This study shows that the geographic isolation caused by the unique topography on the eastern side of the Qingzang Plateau has profoundly affected the genetic diversity and genetic structure of white birch. The marginal populations located in the Yunnan area have already faced the risk of reduced genetic diversity and should be given priority protection.

Aims The riparian forests in the upper reaches of the Yellow River are typically fragile ecologically. However, the frequent extreme hydrological events induced by climate warming may pose increasing threats to ecological stability and security of this fragile ecosystem type. The ecological resilience and adaptation of riparian forests to extreme hydrological events are of key considerations in eco-environmental management of river basins. This paper aims to determine how Tamarix austromongolica, a major tree species in riparian forests of the upper Yellow River basin, responds to extreme drought and flood and explain the resistance and morphology of these riparian plants against environmental stresses.

Methods We selected 47 Tamarix austromongolica trees from three sampling sites along the upper reaches of the Yellow River. Two mutually perpendicular cores were taken from the trunk of the each sampling tree for estimation of the past annual growth, one from the direction facing the slope and the other along the contour of the nearby mountain. We compared the tree-ring growth between cores from the two sides and grouped them according to whether the growth was strongly affected by geohazards. We analyzed the resistance of the two groups to extreme hydrological events during the past 63 years. The statistical growth difference between two sampling directions from each group was performed by using paired test.

Important findings Tamarix austromongolica trees were found to be very resistant to extreme drought events. The diverse sources of water in riparian zones attributed to their stable growth, which helps enhance their tolerance to hydrological drought events. But the trees injured by geohazards appeared to be more severely affected by droughts. The legacy effect in trauma-associated recovery might initiate high sensitivity to interferences. Moreover, T. austromongolica trees are adapted to a wide range of water conditions and their growth did not appear to be substantially affected by flooding. Well-watered condition along with fully hydrated shoots could promote the growth and counteract the potentially negative effects of submergence in T. austromongolica. However, flood induced geohazards, such as mudslides, could have significantly different impacts on growth in different directions, such that the side facing the nearby mountain slope suffered more growth suppression. These processes could lead to modification of morphology. Studying the growth response of T. austromongolica to extreme drought and flood on the upper reaches of the Yellow River will help assess the ecological resilience of ecologically fragile areas and provide a scientific basis for ecological construction and restoration in riparian zones on the Qingzang Plateau.

Aims Our objective is to study the differences between the reproduction characteristics and resource allocation of Saussurea leontodontoides in the fruiting stage across six levels of the elevation gradient, and analyze the relationship between the above two parameters and individual size of S. leontodontoides.
Methods The study site is located in the northeastern margin of the Qingzang Plateau. The collection and investigation were carried out on the fruiting individuals of S. leontodontoides which were distributed in an elevation range of 3 200-4 540 m. 40 complete individuals were randomly collected from each level of the elevation. The number of seeds in each capitulum was counted, then the biomass was measured after drying at 80 °C in the oven. The differences between the reproduction characteristics and resource allocation of S. leontodontoides at different levels of the elevation gradient were analyzed by ANOVA. The relationship between the reproduction characteristics with individual size, resource allocation with individual size at different levels of the elevation gradient was analyzed by the allometric model.
Important findings Our results showed that: 1) The individual size, reproductive organ biomass, vegetative organ biomass, seed number and vegetative allocation were negatively correlated with elevation; the hundred grain mass and reproductive allocation were positively correlated with elevation. 2) Along the elevation gradient, the hundred grain mass, the seed number, the reproductive organs biomass and the vegetative allocation were positively correlated with individual size; reproductive allocation was negatively related to individual size; and vegetative organ biomass and individual size were significantly positively correlated. This indicates that the elevation and individual size had different effects on the reproductive strategy of S. leontodontoides. Our study suggests that S. leontodontoides adapted to the high-elevation stress environment by increasing the reproductive organs biomass and the hundred grain mass.

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

Aims Flower longevity, the length of time that flowers remain open and functional, is an important floral trait that influences plant reproductive success. Prolonging floral longevity can provide reproductive assurance under unfavorable pollination environment, but may suffer some fitness costs. The theoretical models of flower longevity have suggested that there is a trade-off of resources allocation between the flower longevity and attractiveness traits. Flower longevity can adjust according to resource allocation. To understand the potential adaptive significance of flower longevity, it is necessary to disentangle the potential relationships between flower longevity and attractiveness traits (flower size and number) and their effects on female fitness of alpine meadow plants at the inter-species level on the Qinghai-Xizang Plateau.
Methods In the alpine meadows of Qinghai-Xizang Plateau (2 900 m vs. 3 600 m), we assessed how the relationships between floral longevity and flower attractiveness traits of 11 species varied at the inter-species level under different pollination contexts. And we quantified the relative contribution of flower longevity and flower attractiveness traits to the female fitness of plants at the inter-species level at low and high habitats.
Important findings Results show that there is a trade-off between flower longevity and flower number in both low and high altitude communities. And we found that both longer flower longevity and larger flower size increase the female fitness of plants in low-altitude communities, However, the female fitness of plants is only associated with flower longevity in high-altitude communities. Overall, our results suggest that flower longevity is more important for the female fitness in high-altitude plants than low-altitude plants.

The Qinghai-Xizang Plateau and its adjacent highlands host a rich plant diversity, and understanding on how plant species reproduce successfully in those high mountain regions would be of great help for us to discover the evolution and adaptability of plants to the typical alpine environments. Here, we reviewed the progresses of plant reproductive ecology in the Qinghai-Xizang Plateau and its adjacent highlands, with emphases on resource allocation, reproductive mode, evolution of floral traits, etc. We also summarized the impacts of global climate changes on plant reproduction, and the applications of new technologies and methods in this research field to explore the potential mechanisms of plant evolution and adaptation. In the stressful environments of high mountain areas, with the increase of altitude, the reproductive allocation usually shows a trend of increase, and the proportion of resources invested in male function also increases. However, the specific pattern of resource allocation strongly depends on the mating system, individual size, life history, genetic variation and resource availability. In the context of resource and pollination limitation, plants will weight different reproductive modes. Clonal reproduction and self-pollination are conductive to reproductive assurance in populations with pollinator scarcity, while sexual reproduction and cross-pollination can improve seed quality and genetic diversity of offspring, which could benefit population survival in the potential climate flunctations. Therefore, the combinations of different reproductive modes and the generalized pollination networks may be the good choices to adapt to the stressful environments of highlands. The evolution of floral traits might be mainly driven by the selective pressure of local pollinators, but more and more attentions have been paid to the effects of exotic pollinators, herbivores, nectar robbers and abiotic environments such as temperature, precipitation and ultraviolet radiation on floral traits. In recent years, the Qinghai-Xizang Plateau has become one of research hotspots because of its fragility and sensitivity to climate change. Global climate change, characterized by global warming and increased nitrogen deposition, is directly or indirectly affecting the reproductive characteristics of plant species in the region. Climate change may cause shifts of phenology and distribution area of plants and pollinators, which leads to temporal decoupling and spatial mismatch between them. Plants can respond to climate change by adjusting floral traits (floral display, corolla structure, quantity and quality of reward), which may result in changes of type, amount and foraging behaviors of pollinators and affect reproductive success of plants at last. The applications of new technologies and methods could advance our knowledge on plant reproductive ecology. 3D printed flowers could control floral traits precisely and could be employed in examining the effects of subtle changes of floral traits on pollinator behaviors, which would be useful in understanding pollinator mediated selection on floral traits in combination with the uses of commercial pollinators. Importantly, with the development of high-throughput sequencing, the underlying mechanisms of important topics in plant reproductive ecology could be discovered more easily than before, especially in the field of floral evolution. As a conclusion, key issues that need additional attention in the current research as well as the fields worthy of further study are highlighted.

Aims Temperature limit is the main cause of alpine treeline formation. Therefore, it is important to understand the response mechanisms of alpine treeline as well as their tree species under the global climate change. The present study focused on the spatio-temporal dynamics of treeline and ecological characteristics of the tree species in two treeline ecotones.
Methods Two vertical belt-transect plots were established in each treeline ecotone of the Zheduo Mountain and Jianziwan Mountain of the eastern Qinghai-Xizang Plateau. Top and bottom of each transects were lain between species line and forest line, respectively. Detailed information of each tree species treeline, including species name, latitude, longitude, height, age, base diameter, and coordinates, was recorded accordingly.
Important findings The temperatures of the two research areas have increased during the past 58 years. The precipitation has decreased slightly in both the Zheduo Mountain and Jianziwan Mountain. The age structure of Abies fabri from the Zheduo Mountain and A. squamata from the Jianziwan Mountain showed a reversed “J” shape curve and a bimodal shape, respectively. Within the two transects, due to the limitation of seed diffusion, the dominate species showed aggregated distributions at the small scale. At the large scale, A. fabri was aggregated at the Zheduo Mountain, while A. squanmata of the Jianziwan Mountain was randomly distributed due to the impact of surrounding environmental factors. Both tree height and base diameter decreased with the increase of elevation. The fir trees (Abies spp.) at the upper part of the treeline ecotone presented an allometric growth, whose height growth rate was higher than that of base growth, while the relationships between height growth and base growth were isometric at almost mid and lower part of the treeline ecotone. Compared with 10 years ago, there was no significant change at the position of treeline and tree species line of the Zheduo Mountain and the Jianziwan Mountain, neither of the tree density in the Jianziwan Mountain. However, the number of trees in the Zheduo Mountain increased by about 25%. Compared with 20 years ago, tree species lines of the Zheduo Mountain and Jianziwan Mountain were shifted upwards by 50 and 30 m, respectively. Besides, their treeline positions were increased by 75 and 40 m, respectively. Furthermore, the number of trees also increased significantly by 220% and 100%, respectively. Therefore, the treeline and its constructive species are mainly affected by temperature at the large spatio-temporal scale, while influenced by temperature and ambient environment at the small spatio-temporal scale.

Aims Changes in snowpack induced by climate change may alter water and heat regimes at the ground surface, thus influencing activities of decomposers and litter decomposition in snow-covered regions. However, effects of snow-depth changes on litter decomposition are unclear. Our objective was to characterize the decomposition dynamics of two contrasting tree species—Korean pine (Pinus koraiensis) and Mongolian oak (Quercus mongolica) in a snow-depth manipulation experiment.

Methods The snow-depth manipulation experiment that included three treatments (i.e., snow-addition, snow-removal, and control) was conducted in a temperate Korean pine plantation in the Maoershan Forest Ecosystem Research Station, Northeast China. Air-dried foliar litter of the pine or oak (10 g litter per bag) was sealed in a nylon litterbag (15 cm × 20 cm). A total of 648 litterbags (3 plots × 3 treatments × 2 tree species × 3 replicates × 12 sampling dates) were placed evenly on the forest floor in October 2014. Three replicate litterbags per species were buried in each treatment plot and sampled 12 times (i.e., freezing onset stage, deep freezing stage, thawing stage, early, middle and late snow-free seasons) during the two-year period (2014-2016) to determine the temporal variation of the decomposition rate. Associated factors (i.e., mean temperature at litter layer, freeze-thaw cycle, available nitrogen and phosphorus at the organic layer) were measured simultaneously.

Important findings Tree species, snow-depth treatment, decomposition stage, and the measured associated factors all influenced the decomposition rates of the foliar litter. The litter mass loss was 52.1%-54.5% for the pine, and 53.9%-59.1% for the oak during the two-year period. The decomposition coefficients for the litter of the two species were the highest in the snow-addition plot, and the lowest in the snow-removal plot. Moreover, the snow-depth manipulation dramatically changed the relative contribution of the mass loss (R ratio) during the snow-covered or snow-free seasons to the yearly total loss. Compared with the control, the snow-addition treatment increased the R ratio during the snow-covered season by 9.1% for the pine and 10.4% for the oak, while the snow-removal treatment increased the R ratio during the snow-free season by 10.4% and 12.7%, respectively. In conclusion, changes in snowpack induced by climate change may significantly affect the foliar decomposition in temperate forests, and also alter the relative contribution of the litter decomposition in the snow-covered and snow-free seasons to the yearly decomposition.

Aims To test the hypothesis that water is the main limiting factor of tree growth at the arid alpine timberline, and to explore the effects of water on growth-climate relationships of Sabina przewalskii along a precipitation gradient in the northeast Qinghai-Xizang Plateau.

Methods Three sides were selected to sample the alpine timberline along a precipitation gradient in the northeast Qinghai-Xizang Plateau: Halihatu National Forest Park in Wulan County (HL, annual precipitation 217 mm), Qushigang in Dulan County (QS, 281 mm) and Hebei Forest Farm in Tongde County (HB, 470 mm). The correlation and response analysis at seasonal and extreme climate year scales were used to examine the spatial variations of the growth-climate relationship of S. przewalskii at different timberlines.

Important findings Our results do not support the hypothesis that water is the main limiting factor of tree growth at the arid alpine timberline. The effect of precipitation on the radial growth of S. przewalskii were consistent across all three sampling sites, while the effects of temperature were different across sites. At HL site (low precipitation), the winter and summer minimum temperature were the main limiting factor of S. przewalskii radial growth, and this relationship did not significantly change in different extreme climate years. At QS site (middle precipitation), the radial growth of S. przewalskii was mainly limited by the minimum temperature in spring and summer, but its effect was weaker than that at low precipitation site. At HB site (high precipitation), the spring temperature had a significant negative effect on tree growth, and the positive effect of spring precipitation on tree growth was significantly enhanced in comparison with those at low and middle precipitation sites, especially in extreme high temperature and drought years. Summer precipitation did not significantly affect tree growth at high precipitation site. Our results did not support the hypothesis that the radial growth of trees at alpine timberline in arid/humid area is mainly limited by water/temperature. However, precipitation at timberline will affect the relationship between tree growth and temperature at different seasons. With the warming and humidification of the northeastern Qinghai-Xizang Plateau, the climatic limiting factors of tree growth in different timberline areas may be complicated.

Aims Gross caloric value (GCV) reflected plants’ capability of converting solar energy. It provided a reliable indicator of plants’ adaptations to environments in perspective of energy conversion and fixation. The aims of this study were (1) to illustrate the characteristics of GCV of aquatic plants on the Qinghai-Xizang Plateau, (2) to explore the geographical and environmental patterns and (3) to discuss the underlying mechanisms in forming the patterns.
Methods In July and August 2015, we collected 533 samples of aquatic plants’ leaves in 143 field sites on the Qinghai-Xizang Plateau, and measured their GCV using SDACM-4000 oxygen bomb calorimeter. Together with mean annual temperature (MAT) of climatic factor and properties of water body, this study compared the differences of GCV among submerged, emergent and floating-leaved plants by analysis of variance (ANOVA) and Tukey’s HSD. We further regressed GCV of submerged and emergent plants against geographical and climatic factors and properties of water body by simple regression to explore the relative effects of environmental factors on GCV.
Important findings On the Qinghai-Xizang Plateau, the mean GCV was (15.95 ± 3.90) kJ·g^-1. Among the three life forms, the rank of GCV was the emergent plants (18.10 kJ·g^-1) > the floating-leaved plants (16.77 kJ·g^-1) > the submerged plants (14.31 kJ·g^-1). With an increasing latitude, the GCV of emergent and submerged plants increased. Only GCV of emergent plants decreased with increasing altitude and temperature. The GCV of emergent and submerged plants increased with increased water salinity. Dissolved oxygen had significant negative effects on emergent plants, while pH value had no significant effects.

Aims Climate warming strongly influences reproductive phenology of plants in alpine and arctic ecosystems. Here we focus on phenological shifts caused by warming in a typical alpine meadow on the Qinghai-Xizang Plateau. Our objective was to explore phenological responses of alpine plant species to experimental warming. Methods Passive warming was achieved using open-top chambers (OTCs). The treatments included control (C), and four levels of warming (T1, T2, T3, T4). We selected Kobresia pygmaea, Potentilla saundersiana, Potentilla cuneata, Stipa purpurea, Festuca coelestis and Youngia simulatrix as the focal species. Plant phenology was scored every 3-5 days in the growing season. The reproductive phenology phases of each species were estimated through fitting the phenological scores to the Richards function. Important findings Under soil water stress caused by warming, most plants in the alpine meadow advanced or delayed their reproductive events. As a result, warming significantly delayed phenological development of K. pygmaea. Warming significantly advanced reproductive phenology of P. saundersiana, S. purpurea and F. coelestis, but not of P. cuneata and Y. simulatrix. In addition, warming significantly shortened the average flowering duration of alpine plant species. The potentially warmer and drier growing seasons under climate change may shift the reproductive phenology of the alpine systems in similar pattern.

Aims Fractal root system is phenotypic plasticity result of plant root architecture to respond to environmental heterogeneity, may reflect the growth strategy of plants to adapt to environmental conditions. Our objective was to explore the relationship between root fractal dimension and fractal abundance of fractal root system of Melica przewalskyi population in response to aspect variation in the northwest of China. Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at 40 plots which were set up along four slope aspects transects with 20 m distance between adjacent plots. Handheld GPS was used to determine the elevation, longitude and latitude of each plot. ArcGIS was used to set up digital elevation model (DEM). Community traits were investigated and six individuals roots of M. przewalskyi were collected randomly at each plot. The samples were cleaned and divided into different organs, then scanning the root with the Win-RHIZO for measurements of fractal dimension and fractal abundance in laboratory, and their biomass were then measured after being dried at 80 °C in an oven. Important findings With the slope aspect turned from north to east, west, and south, the density, height and soil moisture content of the plant community displayed a pattern of initial decline, the height, density, root fractal abundance of M. przewalskyi increased and the root fractal dimension decreased. The root fractal dimension was negatively associated with the fractal abundance in all aspects, but the relationship varied along the slope aspects gradient; there was a highly significant negative correlation (p < 0.01) between the root fractal dimension and fractal abundance at north slope and south slope aspect, whereas the correlation only reached a significant level (p < 0.05) at the east slope aspect and west slope aspect; indicating that there is a trade-off between the root fractal dimension and fractal abundance. In addition, when the slope aspect changed from north to east, west and south, the standardized major axis (SMA) slope of the regression equation in the scaling relationships between root fractal dimension and fractal abundance increased (p < 0.05), indicating that the roots of M. przewalskyi at the droughty southern slope have less branch and more sparse in the same soil volume of root exploitation and utilization. Consequently, the resource allocation pattern on reasonable trade-off between root fractal dimension and fractal abundance in different slope aspect of M. przewalskyi, reflects the relationship between the income and the cost of construction of plant root architecture.

Aims The relationship between stem and leaf growth is a strategy that plant canopy enhances photosynthetic efficiency and competitiveness through configuration adjustments; this relationship indicates the ratio between xylem and photosynthetic area in a heterogeneous environment. Our objective was to examine how Melica przewalskyi modulated leaf and stem traits in adaptation to changes in slope.

Methods In the alpine grassland of Qilian Mountains, Gansu Province, China, 80 plots were set up along four transects corresponding to contrasting aspects with 20 m distance between adjacent plots. A GPS was used to record latitude, longitude and altitude of each plot and ArcGIS software was used for constructing a digital elevation model (DEM) and extracting information on elevation, aspect, and slope. Community characteristics were investigated and 10 random individuals of M. przewalskyi were cut at the soil surface in each plot, and leaf mass, leaf area and stem mass were measured in laboratory. The 80 plots were grouped into 0°-10°, 10°-20°, 20°-30° slope gradients. Stem and leaf traits were log-transformed and then standardized major axis (SMA) estimation method was used to examine the allometric relationships of stem mass with leaf area or leaf mass.

Important findings The stem mass, leaf mass and leaf area of M. przewalskyi gradually decreased, but the leaf number increased, with slope gradient. An isometric relationship was found between stem mass and leaf area in plots within each slope gradient, whereas an allometric relationship was found between stem mass and leaf mass. Melica przewalskyi grown on steeper slopes tended to have smaller leaf area and greater leaf number at a given stem mass, and leaves with greater stem mass had greater leaf mass. A significant difference in the SMA slope among the three slope gradients of the plots suggested that the slope of the growth site constrained leaf area and leaf mass by stem mass, reflecting plant adaptation to heterogeneous environment.

Aims Trade-offs are the basis of the theory on plant life-history strategies, and the trade-off between flower size and flower number is an important determinant of flower biomass allocation. Our objective was to study the changes in the relationship between flower size and flower number in Stellera chamaejasme populations with elevation in Northwest China.
Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at four elevations at intervals of 100 m from 2700 m to 3000 m; a GPS was used to determine the elevation. Community traits were investigated and 45 individuals of S. chamaejasme were collected randomly at each elevation. The samples were cleaned and divided into different organs, and their biomass were then measured after being dried at 80 °C in an oven.
Important findings With increasing elevation, the height, density, and aboveground biomass of the plant communities displayed a pattern of initial increase and then followed by a subsequent decline; the flower biomass in S. chamaejasme increased with increasing elevation, while the flower numbers decreased. The flower size was negatively correlated with the flower number, but the relationship varied along the elevation gradient; there was a highly significant negative correlation (p < 0.01) between the flower size and the flower number at elevations 2700, 2900, and 3000 m, whereas the correlation only reached a significant level (p < 0.05) at the elevation of 2800 m, indicating that there is a trade-off between the flower size and flower number. The elevation of 2800 m appeared to be a switching point where the S. chamaejasme individuals with more but smaller flowers at the lower elevations were transformed into ones with fewer but bigger flowers with increasing elevation. Consequently, a change in the reproductive strategy with a trade-off between flower size and flower number ensures successful reproduction of the S. chamaejasme populations in adverse environments.

Aims This paper studies the resource allocation during flowering and fruiting, as well as the relationship between variations in floral traits and seed characters in Saussurea undulata.
Methods Field sampling and measurements of dry mass were used to evaluate morphological characteristics of S. undulata distributed at different elevations in eastern Qinghai-Xizang Plateau.
Important findings Saussurea undulata invested more resources in the reproductive organs during flowering, whereas it invested more resources in seed during fruiting. The variations in floral traits during flowering led to a decline in seed number and an increase in 100-seed mass in S. undulate during fruiting with increasing elevation, because the species adopted survival strategies that produce less but larger seed to ensure survival of each seed under the extreme environment of alpine meadow in eastern Qinghai-Xizang Plateau.

Aims Trade-off is the basis of life history strategy theory. Elucidation of the trade-off between plant height and branch numbers is important for understanding the phenotypic plasticity of plants under different habitat conditions. Our objective was to examine how Stellara chamaejasme would adapt to changes in slope aspect through trade-off between height and branch numbers.
Methods In a degraded alpine grassland on the northern slope of the Qilian Mountains, Gansu Province, China, 80 plots were set up on sites of four different aspects at intervals of 10 m vertically from the foot of an isolated hill moving upward. Handheld GPS was used to record latitude, longitude and altitude of each plot. Community traits were investigated and five S. chamaejasme plants were harvested randomly on each plot for measuring the plant height, brunch numbers, leaf area, and above-ground biomass. ArcGIS was used to construct the digital elevation model (DEM) and to extract data on elevation, aspect, slope, slope of slope, and slope of aspect for the study sites. The 80 plots were categorized into groups of north, east, south, and east aspects. Generalized additive model (GAM) was used to select the most effective terrain factors, and partial correlation analysis method was used to examine the trade-off between plant height and brunch numbers on sites of different aspects.
Important findings With a change of the aspect from north to east, south and west, the above-ground biomass and cover of the grassland community displayed a pattern of decline―increase―decline; whereas the average height of the community displayed a pattern of increase―decline. Aspect was the predominant terrain factor affecting spatial variations of the height and branch numbers in S. chamaejasme. When the aspect changed from north and east to west and south, the average height of S. chamaejasme populations declined and the branch numbers increased, resulting in a trade-off in the form of an inversed relationship between the height and branch numbers; whilst the specific leaf area increased first and then decreased. The trade-off between height and branch numbers with changes in slope aspect of the habitat reflected the mechanism of biomass allocation under conditions of multiple competitions for resources in diverse habitats and the regeneration strategy for enhanced adaptation in S. chamaejasme populations.

Aims Phenology is a sensitive, integrated indicator of environmental changes. It is important to research the responses of phenological characteristics to environmental changes for understanding interactions between plants and environment, adaptive mechanisms and survival strategies. Our objective is to examine how phenological characteristics of plants respond to nutrient and water conditions in the eastern Qinghai-Tibet Plateau.
Methods Plant phenological characteristics in alpine Kobresia humilis meadow following nutrient and water additions from 2009 to 2011 were quantitatively analyzed by the methods of nested analysis of variance, phonological index and cluster analysis.
Important findings There were no significant differences in either green-up date or senescence date of plants with nutrient addition, but these dates in several dominant species of grasses, sedges and forbs were postponed following N and P addition. The treatments of nutrient and winter moisture addition moved up flowering dates of dominant species (p < 0.01) and green-up dates of forbs (p < 0.05). Effects of nutrient and summer moisture addition were inconsistent. The senescence dates of Elymus nutans and Scirpus distigmaticus were significantly postponed (p < 0.05) and forbs were postponed. Phenological characteristics of different species had significant differences with nutrient addition (p < 0.01): the senescence dates of Potentilla nivea were significantly postponed (p < 0.05), the senescence dates of Scirpus distigmaticus were significantly moved up (p < 0.05), but the different phenology responses of plants to the nutrient addition were based mainly on plant groups, with the green-up dates of grasses mostly postponed but the green-up dates of sedges moved up. Continuance of vegetative growth and vegetative period after fruiting were negative correlated. Phenological characteristics of plants were divided into three groups by cluster analysis. Phenological characteristics of the treatment of nitrogen-phosphorus-potassium mixed fertilizer, potassium and nitrogen-potassium mixed fertilizer addition varied considerably among plant groups. In summary, phenological characteristics of species in K. humilis meadow displayed large differences after moisture addition, but displayed smaller differences after nutrient addition.

Aims The growth relationship between twig and leaf is a strategy that plant canopy structure employs to space resources and enhance photosynthetic efficiency and competitiveness through configuration adjustments. Our objective was to examine how Stellara chamaejasme exploited twig and leaf configuration to explore the effects of slope change.
Methods In the upper reaches of Shiyang river, Gansu Province, China, 80 plots were set up at intervals of 20 m from the foot of a mountain along eight aspects. GPS was used to record latitude, longitude and altitude of each plot. Community traits were investigated and five S. chamaejasme were cut randomly on each plot for measurement of twig length, twig number, leaf area and leaf number. ArcGIS was used to set up digital elevation model (DEM) and abstract slope data of the study site. The 80 plots were divided into 0°-10°, 10°-20° and 20°-30° slope gradients. Values for twig and leaf traits were logarithmically converted, and then the standardized major axis (SMA) estimation method was used to examine the allometric relationship between twig number, twig length, leaf number and leaf length.
Important findings Twig length, twig number and leaf area of S. chamaejasme gradually decreased along the slope gradient. Significant allometric relationships between leaf number and twig length and between twig number and twig length were found to be consistent in all three slope gradients. Growing speed of twig length was greater than the speed of leaf number, and the growing speed of twig number was greater than the speed of twig length. However, there were significant differences in SMA slope in the three slope gradients, suggesting that slope constrains the leaf number and twig number that can be supported by a given twig length.

Aims Pinus densata is the natural diploid hybrid of P. tabuliformis and P. yunnanensis, and is one of a few known examples of homoploid hybrid speciation. In order to describe the adaptive and growth characteristics among the three pine species at seedling stage and clarify the role of ecological selection in interspecific isolation between hybrid and parental species, we conducted a common garden comparative analysis of fitness traits at seedling stage in this species complex.
Methods We investigated 14 adaptive and growth characters in seedlings from 25 representative populations of the three pine species in a typical habit of P. tabuliformis. The 14 traits are germination rate, seedling survival in Aug., Sept. and Nov. 2011, winter survival rate of one-year old seedlings, seedling survival rate in Oct. 2012, rates of bud-set in Nov. 2011 and Oct. 2012, the proportion of yellow, green and purple seedlings, seedling height, ground diameter and crown height of seedlings. Patterns of the variation of these characters were analyzed using multi-factor nested analysis of variance and correlated to geographical factors of each population.
Important findings Most of the traits were significantly differentiated among species and among populations at seedling stage, and the large amount of variance were partitioned among species or among populations. Germination rate, the rates of bud-set in two years, and the survival rate in Oct. 2012 of two-year old seedlings were the best indicators of among-species divergence. P. tabuliformis showed the highest values in most of the traits and appeared as more fit in its native habits than the other two pines. P. yunnanensis was at disadvantage in several critical traits, e.g. the survival rates of Aug., Sept., Nov. 2011 and rates of bud-set in two years. Most of one-year old seedlings of P. yunnanensis have not bud-set at the end of Nov. and the proportion of yellow seedlings were highest and its survival rate in Oct. 2012 was zero, which illustrates its low fitness in P. tabuliformis habitat. The hybrid pine, P. densata was intermediate between the parental species in most of traits except indice of the proportion of purple seedlings. The populations from the ancestry hybrid zone in the northeast of P. densata range coped with the test site environment better than the populations from the western range. Our study highlights the role of ecological selection in speciation of this homoploid hybrid pine.

Aims Our objective is to study the variation in floral traits of Saussurea stella in 20 populations in response to elevation and mean plant size on the East Qinghai-Xizang Plateau.
Methods We used population means to evaluate sources of variation in reproductive allocation within species. In addition, we used the sample investigation method and dry weight to evaluate biomass.
Important findings Reproductive allocation is negatively correlated with mean plant size. There are trade-offs of resource allocation in reproductive biomass and vegetative biomass, capitulum number and its weight, male and female as well as filament and pollen. Additionally, there is a relationship between variation in floral traits of S. stella and elevation. Consequently, the variation of floral traits ensures that S. stella pollinates effectively and completes sexual reproduction.

Aims Our objective was to determine the distribution pattern and climate characteristics of Kobresia in China.
Methods Distribution information was collected from the literature and floras. Climate information was collected from China’s meteorological stations. ArcGIS software and cluster analysis methods in SPSS software were applied to analyze data.
Important findings Kobresia is mainly distributed on the Tibetan Plateau and in northern China. Fifteen species have wide distributions, and ten have disjunct distributions. The ranges of elevation, latitude and longitude of Kobresia’s distribution are 1400-5 000 m, 23-46° N and 81-112 °E, respectively. Mean values of climatic factors are Holdridge annual biotemperature of 4-19 ℃, annual mean air temperature of 0-20 ℃, annual mean maximum and minimum air temperatures of 7-28 and -6-16 ℃, respectively, extreme high and low air temperatures of 25-40 and -37-0 ℃, respectively, mean air temperature in January and July of -14-13 and 11-24 ℃, respec- tively, highest air temperature in January and July of -7-23 and 18-30 ℃, respectively, lowest air temperature in January and July of -22-7 and 5-20 ℃, respectively, mean air temperature in spring, summer, autumn and winter of -4-19, 9-23, 6-21 and -11-15 ℃, respectively, Kira warmth index and coldness index of 23-159 and -36-0 ℃, respectively, annual precipitation of 154-1500 mm, precipitation in spring, summer, autumn and winter of 19-135, 53-662, 48-545 and 5-92 mm, respectively, Holdridge annual potential evapotranspiration of 261-1100 mm, Thornthwaite annual potential evapotranspiration, aridity index and humidity index of 399-895 mm, 67-786 and 179-816, respectively, and sunshine duration from April to October of 990-2100 h. Generally, there is a high richness of Kobresia under lower or medium mean value of thermal factors, medium mean value of pre- cipitation, aridity or humidity or higher mean value of sunshine duration. As for extreme value of climatic factors, the range for minimum-maximum value of annual air temperature, the range for minimum value of extreme lowest and maximum value of extreme highest air temperature, air temperature range for minimum value in coldest and maximum value in hottest month, air temperature range for minimum value in winter and maximum value in summer are -6-21, -12-28, -48-42, -32-33 and -20-25 ℃, respectively, and the ranges for minimum-maximum values of annual precipitation, aridity index and sunshine duration from April to October are 15-1800 mm, 7-890 and 701-2 300 h, respectively. There is a high species richness of Kobresia under lower and medium extreme values of thermal factors, medium extreme value of precipitation, aridity, and higher extreme value of sunshine duration. The results suggest that Kobresia in China is primarily adapted to microthermal subhumid or mesothermal humid climatic types.

Aims Stipa purpurea is the dominant species in alpine arid and semi-arid grasslands on the Tibetan Plateau. Our objectives are to determine if this species exhibits a strategy shift in its specific leaf area (SLA) to nitrogen (N) concentration relationship along a rainfall gradient and to detect possible effects of environmental factors on related leaf traits.
Methods We investigated variations in leaf traits of S. purpurea associated with climatic and soil factors along an east-west transect with a rainfall gradient (69-479 mm) but similar altitudes (4 300-4 700 m). Five locations from east to west are Damxung, Namco, Gêrzê, Mount Qomolangma and Rutog. We measured SLA, mass- and area-based leaf N concentration (N_mass, N_area), leaf density and thickness and soil total N along the transect.
Important findings In pooled data, SLA and N_mass varied little with the growing season mean temperature and precipitation and the soil total N concentration. The SLA-N_mass relationship in S. purpurea did not shift between the semi-humid areas (ratio of rainfall to evaporation > 0.11) and the arid and semi-arid areas (ratio < 0.11), although there was a positive correlation between SLA and N_mass across the five locations. Variation in SLA was mainly determined by leaf density in the semi-humid areas and by leaf thickness in the arid and semi-arid areas; both were negatively correlated with SLA. With increasing temperature or declining precipitation, leaf density decreased and leaf thickness increased, leading to non-significant relationships between SLA and climatic factors. The increase of leaf density in the semi-humid areas was correlated with the increase of N_area, but the increase of leaf thickness in the arid and semi-arid areas did not lead to change of N_area, resulting in unchanged N_area along the rainfall gradient. A positive correlation was detected between aboveground biomass and N_area in S. purpurea, indicating that increased N_area may increase plant productivity. Our findings suggest that alpine plants in arid and semi-arid areas may maintain a constant N_area by increased leaf thickness in order to achieve a similar photosynthetic productivity and water use efficiency compared to the relatively humid areas. The relative impacts of leaf density and leaf thickness on SLA shifted between the semi-humid areas and the arid and semi-arid areas, which may provide insight in detecting the threshold of water limitation in alpine grasslands.

Aims The study of reproductive allocation is important to understand the environmental factors that contribute to population differences and species evolution. Our objective is to examine variation in reproductive allocation among 30 populations representing three Saussurea species across an elevation gradient on China’s Qinghai- Tibetan Plateau.
Methods We used population means to evaluate sources of variation in reproductive allocation within species. In addition, we used the sample investigation method and dry weight to evaluate biomass.
Important findings Reproductive allocation is negatively correlated with mean plant size; however, this relationship is not statistically significant when the effect of elevation is controlled statistically. Among populations within species, reproductive allocation increases with elevation, and this relationship persists even when the effect of mean plant size is controlled statistically. Altitude is a main influence on reproductive allocation.

AimsArtemisia wellbyi, A. younghusbandii and Sophora moorcroftiana are the major psammophyte populations on the aeolian desertified land in the riparian ecotone of the middle reaches of the Yarlung Zangbo River. Our objectives were to determine how spatial scales are related to population patterns and how species spatially adapt to semi-arid conditions in the riparian ecotone, as well as to provide theoretical foundation for vegetation restoration on sand dunes in the study area.

Methods We selected four representative plant communities under different habitat conditions in the riparian ecotone, measured the position, height and crown diameter of each individual in a 20 m × 30 m plot and studied the population structure, spatial distribution and association of these psammophyte populations using point pattern analysis.

Important findings The population structure of A. wellbyi on semi-exposed sandy gravel land and semi-fixed sandy land is that of a growing population, while A. younghusbandii and S. moorcroftiana on fixed sandy land both have the structure of a declining population. Artemisia wellbyi and A. younghusbandii both have a clumped distribution at different scales, while the distribution pattern of S. moorcroftiana changed from clumped to random to clumped to random as the scale increased. Spatial distribution is mainly determined by the smaller size classes, while fluctuations or changes of population distribution are mainly determined by the larger size classes. There is a scale effect among the studied populations, and positive spatial association occurs mainly at certain scales. Spatial association is often affected by plant size and environmental heterogeneity. The spatial association of A. wellbyi and S. moorcroftiana on semi-exposed sandy gravel land or semi-fixed sandy land changes from independent to positive to independent to positive. The spatial association of A. wellbyi and Oxytropis sericopetala on semi-exposed sandy gravel land changes from positive to independent to positive to independent to negative, and that of A. younghusbandiiand S. moorcroftiana changes from positive to independent. The degree of aggregation weakens with increasing plant size. The smaller size class has a clumped distribution, and the larger has a random distribution or random and clumped. The positive spatial association between different size classes of the same species appears to weaken when the difference of plant size becomes greater and even changes into negative spatial association, while the spatial association of various size classes at a smaller scale often is positive or independent.

Aims Kobresia humilis meadow is a disturbance-dependent (disclimax) community resulting from long-term and heavy grazing. Our objectives were to (a) examine how the compensatory growth of K. humilis (including ramet density, compensatory height and compensatory aboveground biomass per ramet) varies with different levels of clipping, fertilizing and watering and (b) examine changes in specific leaf area (SLA), lamina net photosynthetic rate (P_n) and relative growth rate (RGR) in order to reveal the compensatory mechanisms of the species.

Methods Our field experiment was carried out at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2009. The experiment used a split-plot design with clipping treatment on the whole plot (stubbled 1 cm, 3 cm and unclipped) and both fertilizer (fertilized and unfertilized) and water (watered and unwatered) treatments in subplots. We analyzed effects of clipping, fertilizing and watering on the response variables by multivariate ANOVA. We used stepwise regression analysis to determine the contribution of SLA, P_n and RGR to compensatory growth and Pearson’s correlation to determine the correlation among ramet density, compensatory height and compensatory aboveground biomass.

Important findings Compensatory height and SLA were reduced after clipping; RGR of ramet height and aboveground biomass, ramet density and compensatory biomass were increased. Fertilizing can increase ramet density, compensatory height, compensatory biomass, RGR of ramet height and aboveground biomass, SLA and P_n. The effect of watering on compensatory height and RGR of ramet height under stubbled 1 cm clipping was not obvious, but reduced them under stubbled 3 cm clipping. The interactions of clipping, fertilizing and watering showed that the relation between clipping and fertilizing is “antagonistic” and the relation between clipping and watering is “cooperative”. Although K. humilis appeared under compensation in plant height, fertilizing could enhance the compensation ability and promote tolerance against defoliation at a certain level of clipping.

Aims The formation and changes of patches has an important effect on population patterns. Our objectives are to determine 1) how patches are formed during the process of Stellera chamaejasme population dispersion, 2) what is the effect on pattern during forming and changing of the patch and 3) what roles the formation and changes of the patches play in population dispersion.
Methods We studied five 2 m × 2 m plots of different S. chamaejasme cover in the upper reaches of Heihe, China, using the point pattern method to analyze population pattern, size and density.
Important findings With increasing cover, the population density and territory density tended to increase, decrease, and then increase and the number of the S. chamaejasme population tended to increase and decrease in turn. In the study area, the pattern under 31%-40% cover at all scales was a random distribution. Under the cover of 41%-50%, 51%-60%, 61%-70% and 71%-80%, the distribution pattern was random—clumped—random or regular—random—clumped—random and the clumped density was different. It formed patches during the process of S. chamaejasme population dispersion, which was clumped for external and random or regular for internal S. chamaejasme population dispersion through which patches combine and annex.

Aims Plant growth and substance allocation are greatly affected by temperature change, and the response modes have been shown to vary for different functional groups (graminoids and forbs). Our main objective was to assess how experimental warming affects growth in different functional groups and how they adapt to experimental warming by different substance allocation and structural adjustment.

Methods We selected three dominant plant species, graminoid Elymus nutans and forbs Rumex acetosa and Potentilla anserina, in an alpine meadow in Northwestern Sichuan, and adapted open-top chambers as passive warming devices to generate an artificially warmed environment. After three years of warming, we measured biomass accumulation and substance allocation of the three species.

Important findings Compared to the control, experimental warming significantly increased SLA (specific leaf area) and biomass accumulation of E. nutans and R. acetosa and significantly decreased SLA and biomass accumulation of P. anserine. Warming significantly increased leaf biomass of R. acetosa, but its root biomass significantly decreased; however, warming significantly decreased leaf biomass and stem biomass of P. anserine and its root biomass significantly increased. Warming significantly increased root C concentration of R. acetosa, but decreased root N concentration. Warming significantly increased the LMR (leaf mass ratio), RMR (root mass ratio) and R/S (shoot/root biomass ratio) of R. acetosa, but its SMR (stem mass ratio) significantly decreased. For P. anserina, warming significantly increased its RMR and R/S, but its SMR and LMR significantly decreased. Warming significantly increased C and N allocation in leaves of R. acetosa, and also significantly increased C allocation in its roots, but C and N allocations in its stem were significantly decreased. For P. anserina, warming significantly decreased C allocation in its leaves, but C and N allocations in its roots were significantly increased.

Aims Position-effect of seeds within inflorescences of flowering plants is a common phenomenon, but its influence on seedling establishment is not well known. Our objective was to determine: 1) the pattern of seed production within inflorescences in Ligularia virgaurea (top, middle and bottom of inflorescences) and 2) if position-effect exists, whether it affects seed germination and seedling establishment.

Methods We surveyed seed production of L. virgaurea in the field, seed germination under an alternating temperature regime (15 °C / 5 °C; 12 h light/dark) in the laboratory and seedling establishment under 25% shade by potted plants in the field. One-way ANOVA was used to determine the effects of seed position on seed set, seed weight, ovule number, seed number, germination percentage, initial germination time, emergence percentage, survival percentage, root-shoot ratio (R/S), total biomass (TB) and net photosynthetic rate (P_n). Tukey’s test was used to determine the difference between average values.

Important findings Seed production of L. virgaurea is affected significantly by position within an inflorescence: seed set and seed mean weight are greatest at the top, mean number of ovules is highest at the bottom, and the middle position has the most seeds. Initial germination time is earlier for seeds from the bottom than top, germination percentage and emergence percentage are not significantly different among different positions, and survival percentage among three positions is nearly consistent. R/S and P_n are top > bottom, but TB is not significantly different. Seedling traits are consistent under two different rates of fertilizer application. Results imply that the seeds from different positions have inherently different germination and seedling growth strategies. Top seeds can disperse further and have stronger seedling establishment ability than bottom seeds. Therefore, top seeds have greater ecological significance for sexual recruitment, regeneration and colonizing new habitats.

Aims Compensatory growth is affected by defoliation ratio, water and soil nutrient availability, but it is unclear which factor is most important in the overcompensatory response to herbivores in a particular area. Our objectives were to examine how compensatory growth of Carex scabrirostris varies with different habitats in an alpine Kobresia humilis meadow and determine relative effects of these factors on compensatory growth.

Methods Our field experiment at the Haibei Research Station of the Chinese Academy of Sciences from April to September 2007 included three habitats (habitat I: pen pasture, grazed × high nutrient availability; habitat II: pass pasture, grazed × low nutrient availability and habitat III: ungrazed pasture, null defoliation ratio × low nutrient availability) with three plots per habitat. In each plot, 12 quadrats (0.5 m × 0.5 m) were divided into two groups: 6 caged and 6 uncaged. For each of these sets of 6 quadrats, 3 quadrats were sampled in mid-June and 3 in mid-August. We used canonical correspondence analysis (CCA) with potential impact factors selected by the forward selection procedure for the compensatory growth of C. scabrirostris ramets to determine the relative effects of defoliation ratio, water and soil nutrient variables on compensatory growth.

Important findings The compensatory increase in dry weight, cover, density and height of ramets were higher for the habitat I than for habitats II and III. Overcompensation of aboveground biomass per ramet occurred in habitat I and II, whereas undercompensation was found in habitat III. The biomass allocation to growth function per ramet in habitat I was equal to that of III but higher than that of II. Storage allocation was greatest in habitat II, moderate in III, and least in I. Storage allocation was negatively correlated with growth and clonal propagation allocations, and growth allocation was negatively correlated with sexual reproductive allocation. The most important factors that induced compensatory growth were relative growth rate and soil organic matter content in June, followed by nitrogen content in August and defoliation ratio. These results suggest that the ramets in nutrient-rich habitat or in nutrient-poor habitat but having a high storage allocation tend to have overcompensation growth. The nutrient-rich habitat can compensate for the negative effects of herbivores and improve the ability to tolerate herbivores.

Aims Betula utilis is an important plant in the timberline ecotone of subalpine regions, Western Sichuan China. Our objective is to determine how this species changes its photosynthetic parameters under warming conditions.

Methods We studied the responses of gas exchange to simulated global warming using the open-top chamber (OTC) method. During the 2007 growing season, microclimate data between the OTC and the control (CK) were taken at 15-min intervals with an automatic recording system. In mid-August, the gas exchange of B. utilis seedlings in the OTC and the CK was measured with the LI-6400 Portable Photosynthesis System and a 6-cm² leaf chamber. Comparisons between the OTCs and the control plots were analyzed by the Wilcoxon’s signed ranks test.

Important findings Warming significantly increased instantaneous leaf net photosynthetic rate (P_n), conductance (G_s) and transpiration (T_r) by 17.4%, 21.4% and 33.9%, respectively, and reduced leaf N concentration by 12.4%. Warming also enhanced the maximum net photosynthetic rate (P_nmax) (+19.6%), dark respiration rate (R_d) (+14.3%) and apparent quantum yield (AQY) (+7.9%), but did not influence the light compensation point (LCP) or the light saturation point (LSP) of B. utilis seedlings. Moreover, warming markedly increased the maximum rate of RuBP carboxylation (V_cmax) and rate of photosynthetic election transport (J), but there were no clear differences between treatments for triose phosphate use (TPU) and compensation CO₂ (CCP). Our results indicated that in situ experimental warming had positive effects on the gas exchange of B. utilis seedlings. These responses could be helpful for the timberline species to adapt to future global warming.

Aims Gentiana lawrencei var. farreri (Gentianaceae), a late-autumn or early-winter flowering alpine perennial, is distributed mainly in the northeastern Qinghai-Tibetan Plateau (QTP). The environment of the QTP is harsh because temperature is low and insects are scarce. Our aim is to examine the pollination ecology of G. lawrencei and its adaptive relationship with the environment.
Methods The pollination ecology of G. lawrencei was documented for three consecutive years in northeastern QTP. The breeding system was tested and floral visitors were observed during the flower life span. Flower longevity was recorded and stigma receptivity was tested by the seed-set ratio of different days in which the stigma was presented.
Important findings The seed-set of G. lawrencei under natural conditions was extremely low because of pollen-limitation. Combined characters of herkogamy and incomplete dichogamy indicate that pollinators are needed for complete pollination. Some individuals of G. lawrencei could produce seeds under bagging without emasculation, and it may be from selfing caused by thrips and ants. Bombus kashmirensisand B. sushikini are effective pollinators of G. lawrencei, but the frequencies of visits are extremely low (0.006 and 0.005 time·flower^-1·h^-1, respectively). Floral longevity and stigma receptivity are relatively long compared with other Gentianaceae species, and these increase the probability of pollination chances under low temperature and low pollinator conditions. The combination of self- and cross-pollination, as well as the prolonged floral longevity and stigma receptivity, may be the main reason for the survivorship of G. lawrencei.

Aims We predict that limited resources can enhance the trade-off between size and number of capitula and seeds, showing a strategy of plants. We used Saussurea japonica to investigate the relationship under different levels of light and nutrition. Our objectives are to determine 1) effects of different light and nutrition levels on characters of capitula and seeds, 2) the relationship between size and number of capitula and seeds under different light and nutrition levels and 3) whether the limitation of light and nutrition enhances the trade-off between size and quantity of capitula and seeds.
Methods We planted S. japonica in pots under four treatments: combination of two light levels (high and low) and two nutrition levels (high and low). We counted and weighed (after oven-drying at 80 °C for 72 h) capitula and seeds.
Important findings The treatments of light and nutrition had no significant effects on the number of capitula, while the effects on the mass of capitula were significant. The different treatments had significant effects on both size and number of seeds. Moreover, the relationships between size and number were influenced by different treatments of light and nutrition: under control and low nutrition level, significant positive correlations were observed between size and number for the capitula and seeds; however, significantly negative correlations between size and number were found for the capitula and seeds at the low light treatment and the low light + low nutrition treatments, exhibiting the size-number trade-off. Results suggest that environmental stress (such as low soil nutrition and limited light) enhanced the trade-off between size and number of capitula and seeds, consistent with our prediction. The trade-off can be a response of S. japonica to varied environments, which may improve the adaptability of this plant.