Interactions between crop residue and soil organic matter quality and the functional diversity of soil microbial communities

The effect of crop residue and soil organic matter (SOM) quality on the functional characteristics of soil microbial communities was investigated. Five shoot and root materials with contrasting biochemical qualities were incorporated into soil taken from a cultivated field (FC) and a field edge (FE). These soils had contrasting native SOM qualities, with organic C contents of 0.9 and 2.5%, respectively. The amended soils were incubated under controlled environment conditions before the metabolic characteristics of the soil microbial community were determined by analysis of the activities of 19 hydrolytic enzymes, by substrate utilization within Biolog GN microplates, and C and N mineralization dynamics. For enzyme and Biolog data, metabolic diversity and community level physiological profiles (CLPP) were determined by calculating Shannonʹs diversity index and performing canonical variate analysis, respectively. Soil type significantly affected mineralization of N from the residues, although the size and direction of the effect varied according to the crop residue material added. Both enzyme and Biolog metabolic diversity were affected by the type of crop residue incorporated. Enzyme diversity was higher in FE relative to FC soil, but soil type had no effect on metabolic diversity recorded in Biolog microplates. There were significant interactions between soil type and crop residue material for respiration, N mineralization and enzyme diversity. During the early stages of decomposition, there were similarities in the response of enzyme and Biolog CLPP to crop residue quality and soil type. In the high OM soil, there was evidence for convergence of CLPP in treatments receiving low and high quality crop residue types. However, in the low SOM soil, CLPP of low and high quality crop residue treatments were clearly different. The length of time required for the CLPP of residue amended soil to converge with that of unamended control soil depended on both residue and soil type. We conclude that both crop residue and SOM quality can affect the functional diversity of the soil microbial community, and that enzyme and Biolog analyses reflect complementary, but not inter-changeable, analyses.