Linking microbial community composition to function in a tropical soil

If changes in the composition of the soil microbial community alter the physiological capacity of the community then such changes may have ecosystem consequences. We examined the relationships among community composition (PLFA), microbial biomass (CFDE), substrate utilization profiles (BIOLOG), lignocellulose degrading enzyme activities (β-glucosidase, cellobiohydrolase, β-xylosidase, phenol oxidase, peroxidase), and nutrient releasing enzyme activities (phosphatase, sulphatase) in a Tropeptic Haplustol soil. The soils supported a tropical forest and pineapple plantations of varying ages that were at different stages within the management cycle. Conversion from forest to agriculture significantly decreased %C and %N of the soil by 50–55%, microbial biomass by 75%, β-glucosidase by 54%, sulphatase activity by 85%, decreased Ca, Mg, and Mn availability, and produced compositionally and functionally distinct microbial communities. Total enzyme activities were generally correlated with %C, %N, microbial biomass and, occasionally with community composition. We calculated the specific activities of the enzymes assayed (enzyme activity per unit microbial biomass C) in order to normalize activity to the size of the microbial community. Values for enzyme specific activities were more highly correlated with community composition than were total enzyme activities. In addition, BIOLOG was not correlated with community composition or enzyme activities. Enzyme activities and specific activities may provide a useful linkage between microbial community composition and carbon processing.