Community Succession And Photosynthetic Characteristics Of Pasture Plants In Sub-alpine Meadow In Gannann

There have been a series of problem of environment pollution, such as the lack of resources, damaged of biodiversity and climate change, which pose grave threats to natural ecological balance. Ecological restoration is an important topic faced by the current human being, only respecting the laws of nature did we make ecological system get really recover on the function and landscape level. Succession is the necessary way of plant ecosystem degradation and development, succession theory has important practical significance to explain and guide the ecosystem restoration to the original state. The plant community succession show mainly the change of composition, structure and function of plant community caused by the replacement of species, these changes and plant physiological characteristics in different succession stage are inseparable. Photosynthesis is the basic guarantee for the survival and development of green plants, the changes of plant photosynthetic physiological characteristics on succession gradient reflect plant adaptation mechanisms to different living situation, these related research has certain theoretical significance for vegetation restoration. In this study, a chronosequence of enclosure pasture was established in sub-alpine meadow in Gannan with monitoring species composition, diversity, structure and functioning of plant communities, and PCA sequencing method respectively on qualitatively and quantitatively. Then, measured several photosynthetic physiological parameters of dominants and main species in each succession stage, the results showed :1) Five community succession stages can be expressed as: forb â†' grass â†' legume land â†' sub-shrub â†' shrub. With the succession, the species richness and Shannon index showed a trend of growth basically, and the proportion of the dominants is higher in the early and late than in the middle succession.2)The net photosynthetic rate, transpiration rate, stomatal conductance, water and nitrogen utilization efficiency herbaceous plant greater than bush plant; foliar nitrogen content legume > herb > grass; net photosynthetic rate of the dominant species show unimodal pattern, peak appear in grass group with Elymus dahuricus; PCA analysis showed that: the changes of photosynthetic physiological characteristics in succession gradient is greater than that between species, the capacity of CO2 fixation, water and nitrogen use efficiency are unimodal trend in accordance with the succession.3)There has a certain correlation between the photosynthetic characteristics of plant, there were significant positive correlations between the indexs of obtain material and resources-use efficiency(Aarea, PNUE, WUE), between the indexs closely related to the transpiration(Gs, Tr, WUE) and between the net photosynthetic rate and foliar nitrogen content, however, there was significantly negative correlation between foliar nitrogen content and photosynthetic nitrogen-use efficiency. there also has certain correlation between other indexs, SPAD only significantly positive correlated with Nmass and no significant correlation with other physiological characteristics.4) Community structure and composition mainly affect nutrients and light resource available, leguminous plant can improve nitrogen nutrient, but the leaf nitrogen is also greatly affected by the interspecific competition; Different community height result in the spatial heterogeneity of light resource. In natural conditions, the response of photosynthetic characteristics to different light intensity and nutrient conditions are different, compared with the change of plant photosynthetic characteristics, the positive correlation in different communities and overall between Aarea and Narea is stable.These results suggest that community structure is complicated, the nitrogen, water and light condition of community were changed in the process of restoring succession, and the photosynthetic characteristics among species and succession stages are changed, which reflected the competition and adaptation mechanism of plant in the process of succession. There has certain theoretical guiding significance to master the change of enclosure pasture photosynthetic characteristics in the process of successions for the recovery of degraded alpine meadow.