Aims Gentianopsis barbata displays showy flowers and conspicuous nectaries and has stigma and anthers at different positions (herkogamy) until the fifth day after flower opening. All of these floral syndromes were assumed to favor outcrossing.

Methods We studied pollination biology of this species at Haibei Station on the Qinghai-Tibetan Plateau for three years to test this assumption.

Important findings Contrary to expectation, reproduction in the studied population was mainly through self-pollination. Pollinator visitation was rare, and bagged flowers with anthers set abundant seeds. Both stigma receptivity and pollen viability extended beyond five days. Although stigma receptivity based on seed number decreased after the fourth flowering day, contact of anthers and stigma during floral development resulted in delayed selfing in this species. This delayed selfing retained the floral syndromes and mechanisms for outcrossing, avoided competition between selfing and outcrossing and insured reproduction of G. barbata despite lack of pollinators in arid habitats of the Qinghai-Tibetan Plateau.

Aims Saussurea parviflora is the dominant species on the Qinghai-Tibetan Plateau. This study addresses the following: 1) correlations between S. parviflora's sexual organs and altitude, 2) correlations among S. parviflora's sexual organs, and 3) reasons for S. parviflora's adaptation to this stressful environment.
Methods During the flowering phase in August-September 2005, we collected 11 populations of S. parviflora from different altitudes. We harvested 20 individuals from each population and randomly selected 10 capitula from each individual. We randomly selected 20 flowerlets from different capitula from the same altitude and fixed them in FAA (18:2:2, alcohol:formaldehyde:glacial acetic acid). We measured the length of sexual organs in 20 fully-opened flowerlets and counted pollen in 10 mature flowerlets with undehisced anthers. At the fruiting stage in October 2005 and 2006, we harvested 10 individuals of each population and randomly selected 200 capitula to count the maturation rate. All experimental data were analyzed with the statistical analysis software SPSS11.5.
Important findings There was a strong positive correlation among filament length, anther length and altitude (p<0.01) and a strong negative correlation between pollen number and altitude (p<0.01). Moreover, there were strong positive correlations among 1) style length, length of style ramification and altitude (p<0.01) and 2) style length, length of style ramification, filament length and anther number (p<0.05), and between maturation rate and altitude (p<0.05). Therefore, variation of intraspecific sexual organs under specific environmental condition made S. parviflora adapted to the Qinghai-Tibetan Plateau. With reduced pollen number and insect diversity, abundance and activity with increased altitude, the style ramification lengthened and maturation rate improved. This enhanced the sensitivity to pollinators, ensuring that the decreased pollen was sufficiently spread by them, resulting in increased success of reproduction and dominance in the stressful environment.

Aims A comprehensive survey on anatomical features of the leaves of Carex moorcroftii and Stipa purpurea, two dominant species in Tibetan Plateau, has been conducted. Quantitative analysis on the relation between ecological factors and leaf structure variation was carried out in order to find out how they are acclimated to environments and whether these two species with different reproductive behavior have different adaptation mechanisms.
Methods A transect was set along the Qinghai-Tibet Road from Xidatan to Yangbajing, with great change in ecological features: altitude from 4 586 to 4 901 m, growing season precipitation from 384 to 202 mm, growing season monthly average temperature from 5.1 to 1.4 ℃, growing season monthly average humidity from 65% to 54%, growing season evaporation from 1 242 to 798 mm, and growing season monthly average wind speed from 2.4 to 4.0 m·s^-1. We collected leaf samples along the transect, embedded them in paraffin, stained embedded sections by astra blue-basic fuchsin, and measured them. Variation coefficient, multi-comparison, correlation analysis and regression analysis were used to analyze structural diversity and the relation between diversity and ecological factors.
Important findings The leaf of S. purpurea curls inward, with lower epidermis outside, and stomata and epidermal hairs appear only on the upper epidermis inside. The leaf of C. moorcroftii usually unfolds like “V” in cross section with well-developed aerenchyma, and stomata and epidermal hairs appear only on the lower epidermis. The leaf structure of both species differs remarkably among populations. Multiple linear step by step regressions revealed for S. purpurea that there are significant linkages between soil available K and the size of mesophyll cells, growing season monthly average cloud coverage and lower epidermis thickness, growing season monthly average cloud coverage and phloem area, growing season monthly average humidity and single vessel semi-diameter, and growing season monthly average humidity and average vessel transverse section area. For C. moorcroftii, there are significant linkage between growing season monthly average lowest temperature and upper epidermis thickness, continentality and thickness of bulliform cells, soil pH value and size of upper epidermis cells, soil available phosphorus and vessel numbers, soil available phosphorus and phloem area, and soil available K and leaf aerenchyma area. Comparison of variance coefficients showed that C. moorcroftii had greater integrative variability than S. purpurea.

Aims The Qinghai-Tibet Plateau is characterized by high elevation, thin atmosphere and high solar transparency. Strong solar radiation is a major stress factors during the growing season. Means of defense and dissipation of strong solar radiation rarely have been explored. Our objective is to determine solar utilization and dissipation characters in two native alpine plants, Anisodus tanguticus and Rheum tanguticum.

Methods We used data obtained from a portable pulse amplitude modulation fluorometer (FMS-2, Hansatech Co., UK) to explain the characteristics of utilization and dissipation and components of non-photochemical quenching.

Important findings Strong solar radiation could cause the photoinhibition of photosynthesis, but this constitutes reversible destruction to PSⅡ reaction center in both alpine plants. Quenching analysis of chlorophyll fluorescence indicated thatA. tanguticus could dissipate more excess excitation energy in PSⅡ antennae through non-photochemistry progress thanR. tanguticum, as the fraction of energy utilized in photochemistry was decreasing. Dark relaxation kinetics analysis showed that “fast" component q_Nf was the main fraction of q_N, then “slow" component q_Ns. “Middle" component q_Nm was lower than q_Ns, but it had an increasing tendency accompanied increased light at noon, which indicated that q_Nm still played an important role in non-photochemical quenching. Diurnal variations of NPQ_S and q_Ns were similar in the two plants; the same as q_Nf, rapidly relaxing quenching NPQ_F was also the main component in non-photochemical quenching NPQ, and both NPQ_F and q_Nf were significantly higher in A. tanguticus than in R. tanguticum (p<0.05). The fraction of light energy absorbed in PSⅡ antennae, which is utilized in PSⅡ photochemistry (P), was significantly lower in A. tanguticus than in R. tanguticum (p<0.01), but the fraction that was dissipated thermally (D) was significantly higher in A. tanguticus than in R. tanguticum (p<0.01). The midday depression of the excess excitation that was neither utilized in photosynthetic electron transport nor dissipated thermally (Excess) showed that there was a light stress acclimation in the two alpine plants. The study indicates relatively lower proportion of P and q_P in A. tanguticus than in R. tanguticum and the higher fraction of D and NPQ and q_N, so actual photochemistry efficiency Φ_PSⅡ was lower in A. tanguticus than in R. tanguticum. Higher level of NPQ and q_N mainly results from the NPQ_F and q_Nf, as well as NPQ_S and q_Ns in A. tanguticus compared to R. tanguticum.

Aims Alpine timberlines are ecotones highly sensitive to disturbances and environmental changes that have become a major focus of global climate change research. Sabina saltuaria is an endemic timberline tree in the Qinghai-Tibetan Plateau. It occurs mainly on south-facing slopes and may be useful in ecological restoration of the high-altitude ecosystem. Understanding its ecological characteristics is necessary for understanding its adaptation strategies, as well as the causes and dynamics of timberline patterns in the region.

Methods We established one 0.42 hm² sample plot at timberline >4 390 m on the south-facing slope of Baima Snow Mountain, Northwest Yunnan Province. We recorded height, DBH (diameter at breast height) or diameter at base for seedlings and saplings, and location of each individual. We used a compass and electronic distance-measuring tool to record the location of each individual. We analyzed the size and DBH structure, time-specific life table, survivorship rate, mortality and hazard rate, spatial point pattern of individuals in each age-class and the co-relationships between different age classes.

Important findings Few seedlings occur at timberline in the area of our field survey (about 17 ind·hm^-2, only 1/6 and 1/14 of that of saplings and trees, respectively). Densities declined from trees to saplings to seedlings, and the number of individuals decreased gradually with greater DBH. The survivorship curve was between Deevy type Ⅱ and Ⅲ. The mortality rate curve was similar to the hazard rate curve; both exhibited a peak of mortality at 6-9 cm DBH). Spatial point pattern analysis indicated that most individuals of different age classes had a clumped distribution at different scales (the older the trees, the more aggregative the distribution pattern); however, seedlings had a random distribution at the scale of <14 m. Also the relationships among individuals in different age classes were all significantly correlated with each other. The associations were more significant between seedlings and trees.

Aims In order to understand complex speciation, it is critically important to investigate the corresponding genetic divergence and lineage sorting between close species or taxa distributed in parapatric regions. Our aim was to outline the distribution of the maternally inherited chloroplast haplotypes of Hippophae gyantsensis and H. rhamnoides subsp. yunnanensis and construct their phylogeographic relationships. The former species occurs in central and west Tibet, while the latter is distributed in northwest Yunnan and west Sichuan. These taxa are distinguished by leaf shape, trichomes and fruits.
Methods We sequenced trnL-F and trnS-G DNA fragments for 109 trees of 14 populations from these two taxa.
Important findings A total of 11 chlorotypes were identified, seven in H. gyantsensis and six in H. rhamnoides subsp. yunnanensis, with two shared. Phylogenetic and Nested Clade Analysis analyses further suggested that the divergence of these haplotypes is highly inconsistent with morphological differentiation of the two taxa, suggesting complex maternal lineage sorting between them. These findings refute the previous systematic placements of H. gyantsensis within the genus. However, the available data could not distinguish between two alterative hypotheses regarding origin of this species: homoploid hybrid versus allopatric speciation. In addition, the unique haplotypes recovered in separate populations within each of two taxa suggest that multiple refugia might have maintained both across their distributional ranges during the Last Glacial Maximum.

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 Polygonum viviparum, which is widely distributed in eastern Qinghai-Tibet Plateau in China, is a clonal plant species with two modes of reproduction, clonal propagation by below-ground rhizomes and bulbils and sexual by seeds. This study investigated clonal structure and diversity (monoclonal or multiclonal population) and the relationship between clonal diversity and the altitude. Our objective was to examine the adaptive strategy of alpine plants to varied environments and establish a foundation for understanding reproduction and distribution of clonal plants.
Methods We selected seven populations in eastern Qinghai-Tibet Plateau along an altitudinal gradient and sampled 20 individuals in each population with at least 1 m between individuals to avoid individuals from the same clone. We employed random amplified polymorphic DNA (RAPD) technology for studying clonal structure and diversity and analyzed the relationship between clonal diversity and altitude by SPSS software.
Important findings We selected 13 random primers for amplification and found 117 repetitive loci with 84 polymorphic loci (total average percentage of polymorphic loci was 71.79%). We differentiated 43 RAPD genotypes among the 140 plants sampled. Mean Simpson's index was 0.639, and mean PD was 0.307, slightly higher than the mean of Ellstrand (PD=0.17, D=0.62). There was a clear mosaic among P. viviparum clones, probably because of diverse clonal structure. The formations of P. viviparum populations included guerilla, phalanx and a transitional type. Clonal diversity was independent of altitude.

Aims Pinus densata is an important forest species in the high mountains of the southeastern Tibetan Plateau. Previous investigations demonstrated that this pine originated through natural hybridization between P. yunnanensis and P. tabulaeformis. The mechanisms underlying this hybrid speciation and especially its adaptive evolution are poorly understood. Reproductive fitness plays a critical role in hybrid speciation; however, the fitness of P. densata in the high plateau environment has not been investigated.

Methods We investigated 13 cone and seed characters, related to reproductive potential of the species, from six representative populations distributed throughout its natural range. The 13 characters are cone length, number of scales per cone, number of fertile scales, cone scale density, fertile scale density, ratio of fertile scales, number of seeds per cone, seed length, length of seed wing, total seed length per cone, total length of seed wing per cone, seed productivity per cone and ovule abortion rate. Patterns of variation of these characters were analyzed using one-way ANOVA and correlated to geo-ecological factors of each population.

Important fingdings Characters, such as cone length, total number of scales in a cone and number of seeds per cone in P. densata were similar to that in P. tabulaeformis, P. yunnanensis and several other species of Pinus. The maximum mean value of seed productivity per cone was 74%. One-way ANOVA showed significant (p<0.01) differentiation in all 13 characters among the six populations. Correlation analysis between cone and seed characters and geo-ecological factors indicated that total number of cone scales, number of fertile scales, number of seeds per cone and ratio of fertile scales were negatively correlated with latitude and seed productivity was positively correlated with longitude and ecological gradient axes. All results suggested thatP. densata as a hybrid species is not inferior in reproductive fitness in the plateau environment. The patterns of geographic variations in cone and seed characters seem to be related to the genetic background and divergent ecological environments of the populations.

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 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.

Abies faxoniana forests are one of the major types of sub-alpine dark coniferous forests on the eastern Tibetan Plateau. In the mountainous areas of the upper Minjiang River, it is distributed between altitudes of 2 800-3 800 m a.s.l and usually forms the upper timberline on shaded slopes. To explore the survival status of A. faxoniana populations, ten plots (20 m×20 m) were investigated and analyzed in Gonggangling (33°02′39″ N, 103°43′11″ E). Individual ages were determined using WinDENDRO system or by counting tree branches. Time-specific life tables or vertical life table curves of survival-mortality based and hazard based age structures were drawn. The results showed that: 1) The survival curve of the population conformed to the type of Deevey-Ⅲ; 2) With an increase in the population mortality ratio and a decrease in the survival rate, the mortality ratio greatly increased in ages 0-40 years, reaching 89.7%; 3) There existed two peaks of mortality in the lifespan, one was from seedlings to young trees (0-40 years) and the other in the adult stage (180 years). It is suggested that the mortality rate of A. faxoniana seedlings is impacted most by temperature, wind, snowpack depth, water and other environmental factors.

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 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.

Reproductive allocation and sex allocation are central to plant life-history theory. Especially in recent years, more and more ecologists and evolutionists have focused on the sex allocation theory. Reproductive allocation discusses the trade-off between growth and reproduction, and sex allocation primarily studies the optimal allocation of resources to two sexes, which may explain the diversity of breeding systems in plants. To examine the adaptation of size-dependent resource allocation and discuss the effective factors on resource allocation, the variations of reproductive and sex allocation of five insect-pollinated hermaphrodite species in Ranunculaceae were studied in two populations, located separately at East Tibetan Alpine Meadow (3 500 m) and Sub-Alpine Meadow (2 900 m). Sampling positions were located in Maqu (101°53′ E, 35°58′ N) and Hezuo (102°53′ E, 34°55′ N) in Gansu Province, respectively. From June to September in 2001, we sampled stochastically by the different phenology of five species at floral stage including under- and above-ground parts. The samples collected were individually enclosed into sampling bottles and fixed in FAA (alcohol, formaldehyde, acetic acid, 8∶1∶1). The samples were heated to constant weight for 10 h at 65 ℃. Each individual was dissected into different parts, such as flowers (androecium, gynoecium and corolla etc.), roots, stems and leaves, then were weighed under the Sartorius Balances (10-4 g), and P/O (pollen/ovule ratios per flower) were counted in haemacytometer under the microscope. Individual size is represented by vegetative biomass. Reproductive allocation is the proportion of biomass of total flowers to vegetative biomass; sex allocation is the proportion of androecium biomass to biomass of total flowers. We used the power function Y=aXb to analyse relationships between individual size and reproductive components.Our results showed: 1) in all five species, the reproductive investment increases but the proportion of reproduction (reproductive allocation) decreases with increased individual size, which is consistent with the previous conclusions, indicating size-dependency of reproductive allocation at flowering. 2) there is significant negative size-dependent sex allocation in these species, in that the larger individual allocates more resources to female function (i.e. gynoecium). This means that plants can adjust the resource allocation between the two sexes by its status at flowering to gain higher fitness. However, the relationship between P/O (pollen/ovule ratio) and size is complicated and differs among species. 3) the trade-off between male and female allocation existed, and is influenced by environment. This result confirms the assumption of sex allocation theory

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.

This paper concerns the analyses of niche breadths of and overlaps between several plant species in 3 Kobresia communities in the Haibei Research Station using the formula described by Levins and Pianka. Our results show that the dominant species in the three Kobresia communities have greater niche breaths than their companion species. Kobresia pygmaea have niche breadths of 0.918, 0.896 and 0.910 on the gradients of soil water potential, incident light intensity and slope aspect, respectively. K. humilis and K. tibetica have niche breadths of 0.875 and 0.866, respectively, on the soil water potential gradient. The niche Overlaps are higher between the species that have greater niche breadths than between those that have relatively narrower niche breadths. The niche overlaps show a decreasing trend among congeneric species that have similar biological and ecological characteristics. The niche overlaps between K pygmaea and K. humilis are 0.671, 0.719 and 0.686 on the gradients of soil water potential, incident light intensity and slope aspect, respectively. Our results also show that the niche overlaps between some weeds and high-quality grasses are rather high. This might have been attributable to the suppression of high-quality grasses due to long-term overgrazing and habitat degradation.

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 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 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.

Habitat preference has played an important role in the evolution of the genus Isoetes. Aquatic Isoetes species are generally distributed in oligotrophic softwater. However, it is still uncertain if chemical properties of the water have an impact on the pattern of distribution of Isoetes species. Investigation of habitat preference with regard to water chemistry in natural habitats of species would contribute significance to our understanding of evolution in the genus. Four species of Isoetes are known to occur in China: Isoetes taiwanensis in Taiwan island and I. hypsophila, I. yunguiensis and I. sinensis in the mainland, and their distribution regions do not overlap. All four species are endangered aquatic plants throughout their distribution range in the country.In this paper, 20 parameters of water chemistry in the natural habitats of three species of Isoetes in mainland China were measured, using HANNA Pocket-sized pH Meter HI98107 (resolution = 0.1 pH, accuracy = ±0.1 pH), HANNA Conductivity Meter Dist4/HI983004 (resolution = 0.1 m S·cm-1, accuracy = ±0.1 m S·cm-1) and HANNA C200 Multiparameter Ion Specific Photometer (resolution of NO3-N, NO3-, P, Mn and Mo = 0.1 mg·L-1, accuracy = ±0.1 mg·L-1；resolution of other factors = 0.01 mg·L-1, accuracy = ±0.01 mg·L-1). The character and variation of the chemical properties of the water were analyzed using mean, coefficient variability and difference significance tests (ANOVA and Kruskal-Wallis). Results showed a common character in that there were bigger variations in average and coefficient variability of the 20 parameters. Average Ni was overwhelmingly greater than the other factors, and lower conductivity indicated there was litter pollution in the water. However, of the 20 factors assessed, except for pH (p<0.05), P (p<0.05), NO3-N (p<0.05), NO3- (p<0.05) and Al (p <0.01), the rest displayed no significant difference among habitats of the three species. This indicated that most of the factors (75%) were relatively stable. pH had an identically positive correlation with NO3-N and NO3- (p<0.05); on the contrary, P had an identically negative correlation with NO3-N and NO3- (p<0.05). pH and P were also negatively correlated (p<0.05). Only Al had a positive correlation with P (p<0.05). An analysis, according to data from other research and this study, suggested the significant difference of chemical nature of the water among the three Isoetes species could be due to differences in physiological characters among them, and has no impact on their distribution.

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.

The response of different plant groups to simulated rainfall changes in summer, increased snow in winter and spring, and nitrogen fertilization application in late June were studied in an alpine Kobresia humilis meadow in Qingzang plateau. The results indicated that the response of summed dominated ratio (SDR) and above-ground biomass in different plant groups were not significantly different with 20%-40% rainfall reduction or 20%-40% increased rainfall in 1999. A 100% increase in snow in winter and spring was more favorable to the growth of plant groups than were other rainfall treatments. Both a single late June application of 150 N kg·hm-2 and 300 N kg·hm-2 in soil increased the coverage ratio, height ratio and SDR of grasses. The coverage ratio, height ratio and SDR were significantly decreased at the strong N application (300 N kg·hm-2). There were obvious compensatory effects between grasses and forbs at the application of 150 N kg·hm-2. The sensitivity of the three plant groups was quite different. Grasses were most, forbs were less and sedges were least sensitive to simulated rainfall and available N in the improved disturbing condition. Forbs were most, grasses were less, and sedges were least sensitive to simulated rainfall and available N in the undesirable disturbing condition. It seemed that sedges were most tolerant to fluctuation in environmental resources. Simulated rainfall increasing by 20%-40% could moderate the effect of lower precipitation in a water deficient year (1999), while rainfall decreased 20%-40% could intensify the effect of drought.

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 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.

The number of root forks and link length influence distribution patterns of plant roots. The trade-off between root forks and link length has an important meaning for comprehending ecological adaptation strategy of root architecture. Our objective was to study the relationship between root forks and link length of Melica przewalskyi population in response to slope aspects in the northwest of China.

The study site was located in a degraded alpine grassland on the northern slope of Qilian Mountains, Gansu Province, China. Survey and sampling were carried out in 80 plots that were set up along four aspect transects of a hill with 20 m distance between adjacent plots. A handheld GPS was used to record latitude, longitude and altitude of each plot. ArcGIS was used to set up digital elevation model (DEM) to extract the information of elevation, aspect, and slope for each plot. The traits of plant communities were investigated and three individual samplings of M. przewalskyi were collected randomly in each plot. The samples were cleaned and divided into different organs. The roots were scanned with the Win-RHIZO for measurements of root forks and link length in laboratory, and biomass of different organs was measured after being dried at 80 °C in an oven. The 240 plots were categorized into groups of north, east, west and south aspects of slopes, and the linear regression analysis was then used to examine the trade-off relationship between root forks and link length in different groups.

With a change of the aspect from north to east, west and south, the density, aboveground biomass, height and soil moisture content of the plant community displayed a pattern of steadily declining, while the density, height, root link length of M. przewalskyi increased, and the root forks decreased. The number of root forks was negatively correlated with the link length in all aspects, but the relationship varied along the aspect gradient (p < 0.05). There was a highly significant negative correlation (p < 0.01) between the root forks and link length on north slope and south slope, whereas less significant (p < 0.05) on the east slope and west slope, all indicating a trade-off relationship between the root forks and link length. Consequently, the patterns of resource allocation between root forks and link length in different slope habitats reflected the response and adaption of plant root functional traits to their biotic and abiotic environments and the investment balance mechanism for root architecture construction.

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 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 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.

Aims Seed germination is a crucial plant life history stage related to seedling establishment, survival, fitness and life history expression. Our objectives were to determine: 1) seed germination characteristics of common woody species from the eastern Qinghai-Tibet Plateau and 2) whether differences in seed germination among species are related to seed size, dispersal mode, and mother plant altitude and habitat.
Methods We surveyed seed germination of 61 species under an alternating temperature regime (20 °C/5 °C; 12 h light/dark). We used one-way ANOVA to determine the effects of seed size, dispersal mode, altitude and habitat on final germination percentage and initial germination time, the least significant difference test (LSD) to survey the extent of differences in final germination percentage and initial germination time among dispersal categories and correlation analysis to determine the relationship between seed size and germination.
Important findings Final germination percentages of the species displayed a skewed bimodal distribution, and this implies that dormancy and low and/or continuous germination are the main germination strategies to escape adverse factors. Variances in final germination percentages and initial germination time among species were largely dependent upon dispersal mode, but a few were influenced by seed size, habitat and altitude. Wind-dispersed seeds had higher mean germination percentage (60.6%) and earlier initial germination time (9 d) than those of vertebrate-dispersed (23.4%, 23 d) and unassisted-dispersal seeds (29.5%, 17 d). Findings indicate intrinsic association between life-history characteristics such as seed germination and dispersal mode.

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 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 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.

Variations in leaf characteristics can reflect plant acclimation to environments. We aimed to examine the relationship between leaf traits of Melica przewalskyi and slope aspect.

In alpine grassland of Qilian Mountains, Gansu Province, China, 80 plots were sampled at intervals of 20 m along eight aspects. Latitude, longitude and altitude of each plot were recorded by GPS. At each plot, 10 individuals of M. przewalskyi were random selected and harvested for measurements of leaf mass, leaf area, and leaf volume. A digital elevation model (DEM) was constructed to extract elevation, aspect, and slope for each plot by ArcGIS. The 80 plots were divided into groups of north, east, west and south aspect. Values for leaf traits were log-transformed. the standardized major axis (SMA) estimation method, was used to examine the covariation among leaf traits.

Important findings

Leaf area and leaf volume decreased significantly as aspect turns from north to east, from east to west, and from west to south, but not so for leaf mass, suggesting that leaf thickness increased as slope aspect changes, and thus led to the smaller and thicker leaves on the south-facing slope than that on north-facing slope. A clear allometric relationship between leaf mass and leaf area was found only on the south-facing slope where increase in leaf mass was greater than that in leaf area. While on other slope aspects, an isometric relationships between them was observed. The allometric relationship between leaf mass and leaf volume was found on all four aspects, with the growing speed of leaf volume greater than that of leaf mass, and a rising SMA slope. We can conclude that variations in leaf traits of M. przewalskyi with slope aspect could reflect plant acclimation.

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 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 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 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 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.