Mycorrhizal Colonization Patterns Under Contrasting Grazing and Topographic Conditions in the Flooding Pampa (Argentina)

Abstract

Arbuscular mycorrhizae (AM) can ameliorate the impact of disturbance on agroecosystem sustainability. The objective of this study was to describe mycorrhizal colonization patterns in contrasting grazing situations (exclosure and continuous grazing) and topographical positions (upland and lowland) in the flooding pampa (Argentina). We determined the mycorrhizal colonization of the community as a whole and of Dallis grass (Paspalum dilatatum Poir.), a highly palatable, dominant species. We characterized colonization by the proportion of root length occupied by fungi and their different structures. At the community level, there was higher total colonization in the grazed area than in the exclosure. In contrast, Dallis grass showed higher total colonization and higher proportion of vesicles and arbuscules in the exclosure than in the grazed area. For both levels, colonization was higher in the lowland than in the upland position. Differences were observed only in winter and spring, not in summer. Our results show that 1) continuous grazing is associated with an increase of mycorrhizal colonization at the community level and 2) community-level patterns of mycorrhizal colonization cannot be inferred from dominant species. To our knowledge, this is the first characterization of AM abundance at the plant community level under contrasting long-term grazing conditions in a subhumid grassland.