退化高寒草原土壤生物学性质的变化

Characterization of soil biological properties on degraded alpine grasslands

对藏北退化高寒草原的土壤生物学性质研究表明：轻度退化草地2～10 cm土层微生物（细菌、真菌、放线菌）数量与生物量（碳、氮）、土壤酶（纤维素酶、脲酶、碱性磷酸酶）活性和有机质总体上高于正常草地,中度、严重退化草地则均呈显著降低趋势.微生物生物量碳氮比（BC/BN）与土壤全碳、全氮比（TC/TN）呈极显著正相关（r=0.9088,P≤0.01;n=4）;与正常草地相比,轻度、中度退化草地BC/TC、BN/TN值均呈上升趋势,而严重退化草地则呈明显下降趋势.土壤微生物生物量与土壤酶活性呈极显著或显著正相关,但二者均与土壤放线菌数量呈不同程度的负相关;2～10 cm土层有机质与土壤微生物生物量、土壤酶活性均呈极显著或显著正相关;随草地退化的加剧,2～10 cm和11～20 cm土层腐殖质碳占土壤有机碳比重,以及胡敏酸碳占土壤腐殖质碳比重均较正常草地明显上升.

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 （BC/BN ） and soil total C/N （TC/TN ）, with coefficient value （r） being 0. 9088 （P≤0. 01, n =4）. The ratios of soil BC/TC and BN/TN 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.