Study On Structure And Seasonal Dynamic Of The Primary Productivity In Alpine Meadow

In this paper, changes of basic characteristics of grassland primary productivity under different utilizing frequencies were studied at a typical alpine meadow in maqu county, Gansu province. The results showed that: sedge and gramineous species have higher tolerance to frequent utilization, while forbs are more sensitive to frequent utilization, among which, some species even disappeared under high utilization frequencies, but poisonous species were promoted under frequent disturbances. During the growth season, moderate and frequent utilization (two or three times) in suitable ways to grassland would not cause adverse effects on species diversity, but would favor its increase. In contrast, it would lead to significantly negative effects on species diversity if utilization occurred only once during the late periods of growth season (mid - September) or over four times during the whole growth season. For aboveground biomass, two times (July 15 and September 15) or three times (June 15, July 30 and September 15) were the optimum utilization frequencies, and for output of protein, three times was the optimum utilization way and markedly higher than two times (16%, P < 0.05). Checking stocking capability of grassland in the way of assessing output once at peak period of forage productivity must take account in over-compensation effects produced in practice and revise forage productivity using corresponding variations.In addition ,we also focused on seasonal dynamics of community and studied change characteristics of the primary productivity in grassland community, the results showed that: 1) dynamic changes of communities in different seasons affect the variation of species diversity, further, affecting largely the determination of the primary productivity, species diversity in different seasons presented a growth trend close to single-peak type ,thus the determination and estimate of primary productivity in a period of time need to be improved to provide theory support for accurate determination of the primary productivity; 2) the species composition of communities throughout time series of the whole growing season has always been in a dynamic change process, So the biomass at any time could not accurately reflect the actual production level of community, even when the number of species was the largest, the direct or indirect contribution of about 10 percent of species to the total biomass could be ignored; 3) In natural communities, species diversity, habitat heterogeneity and complexity of interaction relationship among species are bound to lead to temporal differentiation of inter-species / intra-species growth and development stage. This situation has important significance for the balancing seasonal difference of grassland productivity and especially for increasing the balance supply level of available nutrients.