MICROBIAL BIOMASS AND ANTHRONE-REACTIVE CARBON IN SOILS WITH DIFFERENT ORGANIC-MATTER CONTENTS

The microbial biomass C (Cmic) was evaluated by the fumigation-extraction (FE) method in 23 different soils (8 forest soils subjected to acid deposition, 12 sampled from a long-term field experiment and 3 from other arable soils). The hexose microbial biomass C (ARC) was the anthrone-reactive C extracted by 0.5 M K2 SO4 from the 20 h fumigated soil less that extracted from the unfumigated soil. The ratio Cmic to ARC was always lower than 10:1, the average ratio biomass C to carbohydrate C usually observed in microbial cells. Also the significant correlation between ARC and total organic C (TOC) content seems to confirm a release of non-biomass anthrone-reactive C during the chloroform fumigation; however, this solubilization is lower than 0.2-0.4% of the TOC content of soils and it may be considered as negligible. The release of non-biomass anthrone-reactive C seems to be supported by the fact that Cmic values calculated by multiple regression, considering ARC and TOC/100 as independent variables, are closer to observed values than those calculated by the simple regression with either ARC or TOC values. © 1990.