Phytomass Dynamics And The Change Before 24 Years Of The Alpine Meadow In TianZhu

Based on the investigation and analysis of properties of plant communities of Jinqiang River Region in TianZhu County, we have carried on comparative analysis with this dynamic change of phytomass 24 years ago. Four different representative grassland types are selected from Eastern Qilian Mountain. They are Kobresia capillifolia pasture, sedge-grass pasture, grass-forb semi-artificial pasture, Polygonum viviparum pasture,These plots are the former plots in 1981 and 1985. All above grasslands are grazed only by yaks and Tibetan sheep in winter. The structure and composition of the community and quantity characteristic, soil characteristics, aboveground phytomass,belowground phytomass are analyzed. The main research results are as follows:1. composition, structure and species diversity property of plant communities had changed greatly because of long-term grazing on grassland. Species diversity and evenness of plant communities are relatively lower to others, and dominance of communities and richness are relatively high in grass-forb semi-artificial pasture. Diversity index is as follows: Kobresia capillifolia pasture (2.49), sedge-grass pasture (2.74), grass-forb semi-artificial pasture (2.66), Polygonum viviparum pasture (2.86), Evenness index is 0.82, 0.85, 0.76, 0.88. Species diversity and evenness of the community reduce obviously under cultivate measure.2. The soil type belongs to the alpine meadow soil, there is difference among various kinds of plots in Soil characteristics. With 0-50cm depth, soil bulk density increases gradually from top to bottom,But the soil organic carbon, total nitrogen, available potassium, available phosphorus, available nitrogen decreases with the depth of soil, the content in top layer of the soil was more than other layers. C/N was between 17～28.3. Season dynamic of aboveground population phytomass in various kinds of plots take on the obvious " unimodal curve " ,the value of peak appeared in the last ten days of August generally. In growing season, the phytomass of aboveground population have clear differences. The equation of the multinomial simulate season dynamic curve of aboveground phytomass well. Peak value of phytomass (g DM /m2) are 148.67, 157.33, 417.33, 134.00...