Analysis of the phospholipid fatty acids of upland light colored Andosol and the relationship among the size of biomass based on phospholipid fatty acid analyses, microscopical counts and chloroform fumigation-incubation.

摘要

Microbial biomass and community structure in soil were analysed by investigated the amounts and composition of phospholipid fatty acids which had been applied annually with rice straw compost (0, 20, 40, 80 t/ha) and extracted from an Andosol on experimental plots. The phospholipid content increased with increasing compost application levels. The major fatty acids are given. The phospholipid fatty acid composition indicated that the main origin of the soil phospholipids was bacterial membrane lipids. The proportion of the branched chain fatty acids heightened as amount of applied compost was increased. Their proportions in soils in March and April were lower than in October and December; however, the proportions of cyclopropane fatty acids, 16:1omega7 and 18:1omega7, in soils in March and April were higher than in October and December. The results suggest that the ratio of Gram-positive bacteria to Gram-negative bacteria increased under cultivation of wheat. The phospholipid fatty acid content was closely correlated with the available N; the amount of N mineralized during four weeks of incubation at 25 deg C. Significant correlation coefficients between available N and soil content of six fatty acids are given. There were also significant correlations between the counts of bacteria by microscopical method and phospholipid fatty acid content. The proportion derived from soil microbial biomass seemed to be high in soil phospholipid because 23-41% of the soil phospholipid content declined after chloroform fumigation. The size of biomass based on phospholipid fatty acid analyses was higher than the size based on microscopical counts and lower or higher than the size based on fumigation-incubation, depending on the conversion factors.