The effects of large- and small-scale differences in soil temperature and moisture on bacterial functional diversity and the community of bacterivorous nematodes

This paper describes the effects of large-scale seasonal fluctuations as well as experimentally induced small-scale variations of soil temperature and moisture on the community of bacterivorous nematodes and the activity of soil bacteria from a Greek Mediterranean grassland. Our experiment spanned a 6-month period (July-December 1996), during which artificially created changes in temperature (1.4degreesC) and moisture content of the soil (2.3%) were superimposed on seasonal variations of these variables. Functional diversity of soil bacteria was assessed using Biolog GN-plates. Bacterial diversity, richness and evenness as well as the mean oxidation of almost all Biolog substrate groups, were affected significantly by the seasonal fluctuations of soil temperature and moisture, and declined linearly from July to December. The substrates responsible for the differences in monthly soil samples were mainly carbohydrates and carboxylic acids. The small-scale experimental changes in temperature and moisture affected oxidation of only four out of the eight substrate groups. The effect of seasonality was also obvious on the diversity, evenness, richness and total density of soil bacterivorous nematodes, which exhibited higher values during the period September-October. The effect of experimental temperature and moisture modifications varied between the different nematode taxa. Acrobeles, Chiloplacus and Cephalobus responded significantly to small-scale temperature changes, while the responses of the other taxa, if any, were more complicated, depending on the interactive effect of both soil temperature and moisture. In any case, the experimental modifications of moisture alone did not induce significant changes in the structure of the nematode community. After comparing the community parameters of bacteria and bacterivorous nematodes, we conclude that there was no synchronised response between nematodes and their food resources. (C) 2003 Elsevier B.V. All rights reserved.