Overgrazing affects arbuscular mycorrhizae diversity and abundance in Patagonian steppe

VON DUDINSZKY N, CABELLO MN, GRIMOLDI AA, SCHALAMUK S, GOLLUSCIO RA

Hothot

Congreso; X International Grassland Congress; 2008

International Grassland Federation

AMF spore abundance and diversity were evaluated in Patagonian steppe in ungrazed, moderately grazed and overgrazed plots. Soil samples were taken from the rhyzospheric soil of the more conspicuous Patagonian steppe grasses (palatable: Bromus pictus and Poa ligularis, less palatable:Stipa speciosa and unpalatable Stipa humilis) and under bare soil patches. Spores were extracted by the methods of Gerdeman and Nicholson (1863) and Walker et al. (1982). Fungal density was considered as total spore number per 100g of soil. Fungal specific spore density was quantified to calculate the biodiversity index Shannon-Weaver, H. Trap cultures were made for spore identification. AMF spore abundance in general was highest in the ungrazed plots and lowest in the overgrazed ones. AMF community associated with S.humilis was less affected by grazing and showed a higher AMF spore abundance under moderately grazed conditions. AMF fungal diversity was highest in ungrazed and moderately grazed plots and lowest in overgrazed plots. Glomaceae family was dominant in all sites and Gigasporacea family disappeared in the overgrazed sites. Pacispora sp. was present in all sites and it was the first time ever it was found in an Argentinian ecosystem. Overgrazing may alter the ecosystem functioning of the Patagonian steppe not only by reducing the plant cover but also by reducing AMF abundance and diversity, thus increasing the process of desertification.