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Soil nematode activity in and ecosystems is determined by well-known limiting factors such as soil moisture and organic matter. The main aim of our investigation was to determine the composition and distribution of the nematode community in response to soil water and organic content in the rhizosphere of the perennial plant Zygophyllum dumosum. The results demonstrated that soil moisture, organic matter, total nematode population and trophic groups differed under the plants and in the control samples. Significant differences in soil moisture, total nematode population and trophic groups were observed. Bacterial-feeders were found to be the dominant nematode trophic group at the research sites. Bacterial- and fungi-feeders were present in the upper 0-10 cm layer during most of the year. A negative correlation was found between nematodes and soil moisture and a positive correlation was found between nematodes and organic matter. Moreover, trophic structure changes and quantity changes in the nematode community were observed within I month after quantitative changes occurred in the organic matter. Generally accepted nematode fauna indices such as Wasilewska index (WI), F/B, T, H’, lambda, species richness (SR), PPI, maturity index (MI), and modified maturity index (MMI), reflect the temporal changes that occurred in the nematode community during the research period. This study illustrates the integrated effect of soil moisture and organic matter on the activity and structure of the nematode communities existing under plants. (C) 2004 Elsevier SAS. All rights reserved.