Changes in the composition of the plant-feeding nematode community in grasslands after cessation of fertiliser application

The community structure and abundance of plant-feeding nematodes were studied in four grasslands, which had not been fertilised for 6, 10, 23, and 28 years, respectively. We hypothesised that nutritional impoverishment of the grasslands would result in a decrease in the nematode density and biomass, and a shift in the nematode community structure towards species that are better adapted to nutrient-poor conditions. Furthermore, we expected that plant-specific nematode communities are present in the rhizosphere of different dominant plant species. Multivariate analyses showed gradual changes in the nematode fauna after the cessation of fertiliser application. Particularly, during the first 10 years of succession the density and species number of large endo- and ectoparasites strongly decreased resulting in a lower diversity of nematode genera. Root biomass, plant species, and season had a minor effect on the nematode numbers acid community composition. However, within the rhizosphere of single plant species clear community changes were observed with time of non-fertilisation, indicating that qualitative changes within a plant species rather than qualitative differences between plant species affected the nematode community. Most likely, lower nutritional quality of the nematode fond source, due to decreased nutrient concentrations and increased levels of defensive compounds in plant tissues under nutrient-poor conditions, was the major factor affecting the plant-feeding nematode community. Average nematode body size, which is constrained by the absolute amount of food necessary for growth and maintenance, decreased at lower nutrient availability. However, the results suggest that evolutionary adaptation of feeding strategies that reduces the energetic costs of feeding and movement. such as endoparasitism, a longer stylet, and the modification of feeding cells, enabled certain nematode species to support a relatively large body size under conditions of low nutrient availability. (C) 2001 Elsevier Science B.V. All rights reserved.