CHANGES IN SOIL MICROBIAL PROPERTIES AND PHOSPHOLIPID FATTY-ACID FRACTIONS AFTER CHLOROFORM FUMIGATION

A variety of common soil microbial analyses (biomass by fumigation-ext raction, basal-and substrate-induced respiration, various enzymatic ac tivities, potential nitrification, ninhydrin-reactive nitrogen) were c arried out to study the usefulness of phospholipid fatty acids (PLFAs) to detect changes in microbial activity and biomass. Soil fumigation with chloroform was used to disturb microbial activity. The total amou nt of PLFAs decreased by about 50% during 10 days' incubation after fu migation. In comparison with the other methods, the amount of ester-li nked PLFAs gave higher estimations for microbial biomass decline. Addi tionally, we studied the effects of chloroform fumigation on various P LEA fractions that can be used as indicators for certain microbial sub groups. The branched chain fatty acids indicative of Gram-positive bac teria were affected only slightly (ca. 30%), whereas the monounsaturat ed fatty acids, mostly characteristic of certain Gram-negative bacteri a, were more heavily affected (60-70%). The polyunsaturated fatty acid s indicative of eukaryotes had decreased by 70-80%. The non ester-link ed PLFAs and the hydroxy-substituted fatty acids of lipopolysaccharide s were not affected by chloroform fumigation treatments. The methods c ommonly used for soil microbial biomass measurements gave diverse resu lts after a strong decline of the microbial community. (C) 1997 Elsevi er Science Ltd.