Signature fatty acids in phospholipids and lipopolysaccharides as indicators of microbial biomass and community structure in agricultural soils

Abstract

Soil samples were taken from eight long-term agricultural monoculture and rotation experimental plots and examined for their profiles of fatty acids in either phospholipid or lipopolysaccharide fractions. The more specific constituents related to microorganisms were tested for their ability to estimate the biomass and to differentiate community structure.More than100 fatty acids, including unsubstituted, straight- and branched-chain,unsaturated and hydroxy fatty acids were detected in the soils sampled.Good correlations between the total amounts of fatty acids derived from phospholipids and the microbial biomasses and activities obtained by different classical procedures were observed (correlation coefficients were above 0.97). This indicates that the fatty acids were closely linked to soil microorganisms and that this method can be used in the study of soil microbial ecology.In addition,each of the eight soils was characterized by its own pattern of fatty acids, either as phospholipids,or as lipopolysaccharides.This shows that this method has the potential to differentiate between the soils,even on a management level.The most apparent difference was registered in terms of the relation of the monoenoic to the normal fatty acids among the eight soils.The black fallow and the fields cultivated with potatoes showed approximately equal amounts of both, the green fallow and the fields cultivated with wheat displayed a ratio of 1.7:1.0 and the grassland 1.3:1.0. The soil with crop rotation showed considerably more fatty acids in terms of the number in the normal fraction,while the grassland contained more hydroxy fatty acids than the soils from arable land.