Effect of AM symbiosis exclusion on grassland community composition

Experimental data on grassland community response to exclusion of arbuscula r mycorrhizal (AM) symbiosis using fungicide benomyl and to phosphate addit ion were evaluated after four years of continued manipulation using multiva riate direct gradient analysis. While the community responded only to phosp hare application in the third year (phosphate application suppressing forbs in favour of graminoids), the data from the fourth season indicate relativ e suppression of some forbs (including Plantago lanceolata, Cerastium holes teoides) with both phosphate and fungicide applications. Positive response of graminoids to phosphate addition seems to interact with fungicide applic ation, while an important community constituent - Achillea millefolium - se ems to profit primarily from fungicide applications. The effect of the fung icide on the AM symbiosis was confirmed on roots of Planiago lanceolata. Th e direct evaluation of frequency of AM fungal structures in plant roots als o revealed a diverse response of different plant species to phosphate appli cation. Nevertheless, in ail species (except non-mycorrhizal Luzula campest ris), phosphate decreased the frequency of arbuscules and increased the fre quency of non-infected root segments.