Responses Of Plant Species On A Recessive Succession Of Alpine Wetlands In Eastern Tibetan Plateau To Variability In Soil Water Content

Water,as the most important environmental factor in the terrestrial ecosystem,has both ecological and physiological importance in determining distribution and growth of plant species.The differences in the functional traits of plant species reflect the differentation in resources utilization,competition and life-history strategies.The plastic responses of functional traits to changed resource availability(e.g.soil water availability)have been considered as an important measures for plant species to adapt environmental changes.As one of the most sensitive area to climate change,the Tibetan Plateau was expected to suffer intensive fluctuation in precipitation.Therefore water availability would be play an important role in determine the survival,growth and distribution of plant species in this areas,and the recessive successional stages of alpine wetland were among the most affected grassland type.Thus studying of the responses of communities and speices in recessive successional stages of alpine wetland to changed soil water content will help us to understand the responses and adaptations of these species to climate-induced changes in soil water availability in the future,as well as the mechanisms underlying the response and adaptation.In this study,we transplanted individuals and collected seeds from the recessive succession of alpine wetland to examine the responses of aldut plants,seedlings and seed germination to differed water regimes.Our results and conclusions include:1)Water has significant effects on the different levels of performance for plant species in eastern Tibetan Plateau,from leaf morphological and physiological traits to individual size and productivity.And the responses of these plant species to variation in soil water condition were species-specific.2)In the seasonal wetland where featuring with the frequent and intensive water fluctuations over time,the herbaceous plant species gain benefits from increased plasticity in physiology traits and decreased plasticity in morphology traits.We find a contrasting association of morphological and physiological plasticity with plant performance.In this environment with high intra-annual rainfall variability,herbaceous plants with reduced plasticity in leaf morphology and greater plasticity of leaf physiology achieved greater specific-level dominance.Our study helps clarify the role of morphological and physiological plasticity of plant traits for predicting plant performance in an alpine community and suggests that the ability of plants to track rapid changes through physiological adjustments may be a key regulator of species responses to future environmental change.3)For the alpine swamp meadow plant community,which was formed after the degradation of typical wetland,the main compositional species of it showed significantly habitat-specific responses to changed water availability.The responses of species which originate from mature meadow were strongly differed from those which were typical wetland original.Furthermore,the community composition of swamp meadow is likely to remain highly sensitive to changes in water conditions and could be substantially influenced by future water supply;thus,it is unstable.4)Overall,there were significant effects of moderate water stress on the growth of seedlings for species from grassland in eastern Tibetan Plateau,but the response of these species to changed water condition was substantially different between species,suggested that the response of alpine grassland community to water shortage will depend greatly upon their species composition.The average plasticity of these seedlings of alpine grassland common species was low,and there was no significant relationship between the plasticity and the productivity.However,we found there were significant relationships between the traits mean and productivity of these seedlings,indicating that the traits mean was better predictor for the performance of these species than plasticity.5)Soil water avaibility had significant effects on the final percentage of seed germinantion,while its effects on the mean germination time and days to first germination were not signifant.According to previous reports,the phylogeny and other environmental factors,such as temperature determined the germinaton time in our study area.The orginal habitat conditions of these seeds in the sucessonal stage had strong effects on the germination as well.Thus to restoration and protection of these habitats in the recessive succession will need to take consideration of charactoristics of seed germination and its response to water conditions.