Development of a physiological approach to measuring the catabolic diversity of soil microbial communities

A physiological method to assess the catabolic diversity of soil :microbial communities was developed and applied. The method utilises differences between the substrate induced respiration (SIR) : responses of microbial communities to simple organic compounds to quantify catabolic diversity. The investigation was conducted in three stages: (1) selection of suitable substrate concentrations; (2) selection of substrates; and (3) application of the method to assess the catabolic diversity that had developed in soils over long and short periods. The concentrations of substrates giving optimal respiration response over 4 h were determined in four soils (three pasture and one forest) using 12 substrates selected from a range of amino acids, carboxylic acids, polymers and carbohydrates. Maximum SIR response could be obtained generally over a two-fold range of concentrations for most substrates. These results were used to select substrate concentrations for testing the SIR responses of five soils (three pasture, one arable, one forest) to 83 simple sugars, carboxylic acids, amino acids, polymers, amines and amides. Principal components analysis (PCA) and calculation of the standard error of individual substrate responses across soils were used to identify the 36 substrates providing the greatest differences in SIR responses between the five soils. SIR response profiles were determined using 36 substrates in soils under different management (grass pasture, reseeded grass pasture, 2-y pasture ley, arable) and in glucose-amended soil over 3 wk. Analyses revealed that differences in SIR responses between substrates gradually declined with increasing soil disturbance from pasture to arable soils. There were only small changes in catabolic diversity of the arable soil amended with glucose, despite a 1.35-ford increase in microbial biomass C during the first 7 d. The physiological technique provided a reasonably rapid and simple method to assess the catabolic diversity of microbial communities without extracting or culturing organisms from soils. (C) 1997 Elsevier Science Ltd.