Microbial biomass and some biochemical characteristics of a strongly acid tea field soil

Microbial and biochemical characteristics of a strongly acid tea field soil were examined by comparing them with those of other soils of similar type (Andosol) but with different pH values and management conditions. The results of the plate count showed that the numbers of bacteria and actinomycetes in the tea field soil were smaller than those in the cultivated soil with neutral pH. There was a relative abundance of acidophilic or acid-tolerant actinomycetes in the tea field soil. In spite of the low pH, the tea field soil contained larger amount of biomass C and ATP than the cultivated soil with neutral pH. Biomass C/ATP ratio of the tea field soils was smaller than that reported by Ocio and Brookes, due to either a lower content of extractable carbon or higher content of ATP in the soil microbial biomass. Cycloheximide suppressed the CO2 release from the tea field soil amended with glucose by 20% for 3 to 6 h, and 45% for 7 to 24 h of Incubation time, while streptomycin had no effect. Fifty-four % of the activity remained in the soil amended with both antibiotics, suggesting the participation of fungi in the decomposition of glucose as well as that of microorganisms tolerant to both antibiotics. The cultivated soil with neutral pH differed from the tea field soil in the strong suppression of CO2 release by streptomycin. These results, together with the discrepancy between the plate counts and the content of ATP or biomass C, indicated that the microioral characteristics of the acid tea field soil were qualitatively different from those of the cultivated soil with neutral pH. As vanillin is considered to be a model compound for lignin decomposition, the pattern of vanillin decomposition was compared among the tea field soil, the cultivated soil with neutral pH, and a forest soil. The tea field soil decomposed vanillin rapidly, while the decomposition in the cultivated soil with neutral pH was slower. The pattern In the forest soil was similar to that of the tea field soil.