摘要：Sheep overgrazing in grasslands of Tierra del Fuego has determined a decrease of grass cover but an increase in a prostrate shrub of low forage value (murtilla, Empetrum rubrum). We selected soils with different modality of grazing, which determined particular characteristics in soil and vegetation. Abundance and diversity of spores of arbuscular mycorrhizal fungi were studied on the four soils and on three of the most frequent grasses (Festuca gracillima, Deschampsia flexuosa y Poa rigidifolia). Spore counts were measured in rizospheric soil, along with nutrient content (P and N) in plants, and percentage of root length colonised and the morphology of colonisation. The most frequent species was Glomus fasciculatum. The soil, the host plant, and the interaction between both variables influenced total spore counts and percentage of root length colonised. Poa rigidifolia showed the highest number of rizospheric spores and the highest percentage of root length colonised. Neither relationship between spore counts and root colonisation nor relationship between root colonisation and P or N plant contents were observed using the whole data (soils and plants). Total spore counts were correlated positively with measures of N, P, Ca, K and pH in soil. Nevertheless, when soils and plants were studied separately, both the relationship between spore counts and percent of root colonised and its direction depended on the soil-host combination
