Effects of altered soil-water availability on a tallgrass prairie nematode community T.C. Todd * , J.M. Blair, G.A. Milliken Department of Plant Pathology, Division of Biology and Department of Statistics, Kansas State University, Manhattan, KS, USA Received 28 September 1998; received in revised form 17 March 1999; accepted 17 March 1999 Abstract 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 profile. 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. Keywords: Climate change; Community structure; Nematode; Soil moisture; Tallgrass prairie 1. Introduction The Great Plains region of North America is domi- nated by grassland ecosystems whose distributions are determined primarily by an east–west precipitation gradient (Weaver, 1954; Risser et al., 1981). Grassland types range from the xeric shortgrass prairie at the western edge of the region to the mesic tallgrass prairie at the eastern edge. Primary productivity across this gradient is also related strongly to precipitation (Sala et al., 1988). Within grassland types and parti- cularly for frequently-burned tallgrass prairie, often soil moisture is the best predictor of aboveground net primary productivity because it reflects longer-term patterns of precipitation and water use (Knapp et al., 1998). Applied Soil Ecology 13 (1999) 45–55 *Corresponding author. Tel.: +785-532-1350; fax: +785-532- 5692; e-mail: nema@plantpath.ksu.edu 0929-1393/99/$ – see front matter # 1999 Elsevier Science B.V. All rights reserved. PII:S0929-1393(99)00022-0