Spatial Distribution and Successional Pattern of Microbial Activity and Micro-Faunal Populations on Decomposing Barley Roots

Abstract

1. With the current trend in agricultural practice to increase the importance of indigenous and added organic matter in the build-up of soil fertility, a better understanding of the dynamics of decomposition activity around organic resources is required. In this study the changes in microbial activity and populations of protozoa and nematodes were followed in decomposing barley root material buried in soil cores, and in three soil fractions with increasing distance from the root material. 2. Respiratory activity was maximal during the first week and decreased throughout the experiment, and at the last sampling after 392 days no significant effect of the roots on respiration was observed. 3. Following root addition microbial activity (dehydrogenase activity and potential denitrification rate) increased rapidly in the root material and in soil up to 1.8 mm from the roots. Microbial activity peaked after 4 days followed by a peak in protozoan numbers after 2 weeks and a peak in the number of nematodes after 6 weeks. 4. Growth potential of bacteria, as indicated by enzyme synthesis during a potential denitrification assay, and average bacterial cell size was larger on the roots than in the soil suggesting a more active bacterial biomass in this fraction. 5. The root effect was very local, and was limited mainly to the soil fraction adjacent to the roots; soil 1.8-5.4 mm from the roots and soil more than 5.4 mm from the roots was hardly affected by the resource. 6. These results demonstrate distinct successional patterns in the microbial food web with a sequence of population development from micro-organisms to protozoa and nematodes.