Effect of artificial exclusion and augmentation of fungal plant pathogens on a regenerating grassland

Abstract

Plots of rough grassland dominated by Holcus lanatus L. were cleared of vegetation in three successive years and allowed to regenerate without grazing or harvesting. Vegetation cover and foliar disease severity were measured using pin sampling in each plot, two to four times per year. One third of plots were sprayed regularly with propiconazole to reduce fungal disease; one third of plots were sprayed with rust (Puccinia coronata f. sp. holci Corda.) urediospores in the second and third years of the study and with conidia of the leaf-spotting fungus Ascochyta leptospora (Trail) Hara. in the third year. The fungicide had direct effects on the growth of perennial herbs and grasses, and indirect effects through disease control on perennial herbs. Both fungicide treatment and disease augmentation tended to raise diversity in plots where grasses were only partly dominant. Fungicides increased diversity because both direct and indirect effects were greater in perennial herbs than in grasses. Disease augmentation raised diversity because the diseases introduced were more specific to the most common component of the vegetation, H. lanatus.