Changes in soil microbial properties and phospholipid fatty acid fractions after chloroform fumigation

A variety of common soil microbial analyses (biomass by fumigation-extraction, basal- and substrate-induced respiration, various enzymatic activities, potential nitrification, ninhydrin-reactive nitrogen) were carried 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 amount of PLFAs decreased by about 50% during 10 daysʹ incubation after fumigation. In comparison with the other methods, the amount of ester-linked PLFAs gave higher estimations for microbial biomass decline. Additionally, we studied the effects of chloroform fumigation on various PLFA fractions that can be used as indicators for certain microbial subgroups. The branched chain fatty acids indicative of Gram-positive bacteria were affected only slightly (ca. 30%), whereas the monounsaturated fatty acids, mostly characteristic of certain Gram-negative bacteria, were more heavily affected (60–70%). The polyunsaturated fatty acids indicative of eukaryotes had decreased by 70–80%. The non ester-linked PLFAs and the hydroxy-substituted fatty acids of lipopolysaccharides were not affected by chloroform fumigation treatments. The methods commonly used for soil microbial biomass measurements gave diverse results after a strong decline of the microbial community.