Effects of altered soil-water availability on a tallgrass prairie nematode community

Climate change predictions for the Great Plains region of North America include reduced growing season precipitation. The consequence of this prediction for soil fauna and belowground processes was investigated at two spatial scales by integrating experimental manipulation of soil moisture levels with natural variation in soil-water availability. Experiments consisted of (1) reciprocal core transplants across a regional precipitation gradient and (2) supplemental irrigation applied across a local topographic gradient. This report examines functional-level responses by the tallgrass prairie nematode community to differences in soil moisture levels over a four-year period. Effects on nematode community structure were complex and dependent upon nematode trophic habit and depth in the soil pro®le. The strongest and most consistent responses to changes in soil-water availability were displayed by herbivorous taxa, with 71% higher densities observed under wetter soil conditions across experiments and years. Responses of microbial-feeding nematodes were more variable, with lower densities observed, in some cases, in the presence of experimentally-increased soil moisture levels. Effects of regional differences in soil-water availability on the nematode community were uniformly restricted to depths >20 cm. Community responses to short-term changes in soil moisture were not consistent with patterns in community structure developed under different natural moisture regimes, suggesting divergent short-term and long-term responses of belowground biota and processes to changes in soil-water availability. # 1999 Elsevier Science B.V. All rights reserved.