Above-ground grazing affects floristic composition and modifies soil trophic interactions

There are few data on the functional inter-relationships between above- and below-ground components of soil ecosystems. Here, we report changes in below-ground soil invertebrate trophic relationships (manifested as alterations in stable isotope natural abundances, delta C-13 and delta N-15) that arose in association with the removal of sheep grazing and from the resulting changes in above-ground floristic composition. Consequent to grazing removal, Lolium perenne L. (perennial rye-grass) was replaced as the dominant plant species in ungrazed treatments by Ranunculus repens L. (creeping buttercup), a species with more C-13-enriched foliage. Consequently, all invertebrate functional groups studied, but not whole soil, were more C-13-enriched in ungrazed treatments. Earthworms (detritivore) from grazed treatments were significantly N-15-enriched compared with earthworms from ungrazed treatments. In contrast, slug (herbivore) delta N-15 exhibited no treatment effect. Reasons for this are unclear but may be related to the effects of above-ground grazing on the composition of below-ground microbial/microfaunal communities. Omnivores/carnivores (beetles and spiders), were more N-15-enriched than primary producers in the grazed than in the ungrazed treatments (6 vs. 4parts per thousand) suggesting a longer below-ground foodchain in the grazed plots. The cessation of fertilizer application had no comparable effects on below-ground trophic relationships. (C) 2002 Elsevier Science Ltd. All rights reserved.