[Characterization of soil biological properties on degraded alpine grasslands]

The study of degraded alpine grasslands in northern Tibet showed that compared with normal alpine grassland, slightly degraded alpine grassland had higher amounts of soil bacteria, fungi and actinomyces, higher activities of cellulase, urease and alkali phosphatase, and higher contents of microbial biomass C and N and organic matter in its 2-10 cm soil layer, while these parameters were much lower on moderately or severely degraded alpine grassland. There was a positive correlation between soil microbial biomass C/N (B(C)/B(N)) and soil total C/N (T(C)/T(N)), with coefficient value (r) being 0.9088 (P < or = 0.01, n = 4). The ratios of soil B(C)/T(C) and B(N)/T(N) had an increasing trend on slightly and moderately degraded grasslands, but decreased obviously on severely degraded alpine grassland. Soil microbial biomass had a significant positive correlation with soil enzyme activity, and these two parameters were both positively correlated with the amounts of soil bacteria and fungi, but negatively correlated with that of soil actinomyces. In 2-10 cm soil layer, microbial biomass and enzyme activities were significantly positively correlated with organic matter content, and the ratios of humus C/organic C and humic acid C/humus C in 2-10 cm and 11-20 cm soil layers increased significantly with increasing degradation of grassland.