SEASONALITY OF THE SOIL BIOTA OF GRAZED AND UNGRAZED HILL GRASSLANDS

Temporal and spatial measurements of soil microbial biomass, activity and community structure and nematode abundance were made in grazed and ungrazed Agrostis-Festuca and Nardus dominated hill grasslands, with brown earth and podzolic soils, respectively. Microbial biomass and ac tivity were significantly higher in podzolic soils with Nardus dominat ed vegetation, than in brown earth soils with Agrostis-Festuca vegetat ion. Phospholipid fatty acid analysis (PLEA) revealed differences in m icrobial community structure between soils. The ratio of fungal-to-bac terial fatty acids was higher in the brown earth than in the podzolic soil, whereas the diversity (Shannon-Weaver index) of PLFAs was greate r in the podzolic soil. A large proportion of the microbial biomass (5 0%) and activity (40-70%) was within the surface 0-5 cm soil, with red uced amounts at lower depths of 5-10 cm and 10-15 cm. Microbial biomas s and activity and nematode abundance showed pronounced summer maxima and winter minima. The long-term removal of sheep grazing from both gr assland types resulted in significant reductions in microbial biomass and activity in the surface soil. The abundance of active soil fungi, measured as the fungal fatty acid 18:2 omega 6, was significantly redu ced by the removal of sheep grazing, as was the ratio of fungal-to-bac terial fatty acids. Bacterial fatty acids were unaffected by the remov al of sheep grazing. Possible mechanisms for these changes are discuss ed. Numbers of soil nematodes were significantly lower in the ungrazed sites. The effects of removing sheep grazing on nematodes and microbi al community structure were most pronounced in brown earth soils. Fact ors responsible for these changes are discussed. (C) 1997 Elsevier Sci ence Ltd.