CONICET | Buscador de Institutos y Recursos Humanos

The association of soil properties and host plant with arbuscular mycorrhizas was study in a wide range of grasslands affected by a long term sheep grazing modality in the Magellanic steppe of Northern Tierra del Fuego (Argentina). Low pH, high C, low N and low Ca and Mg in soil were associated to vegetation types with high proportion of prostrate shrubs of little forage value; and less acidity, low C:N ratio, high NO3- and Ca and Mg were associated with vegetation types with high proportions of palatable mycorrhizal grasses such as Poa rigidifolia and Deschampsia flexuosa. These two plants were present at all the studied sites but in different cover proportions, and their rizopheric soil contained different abundance of AM fungal spores. Spore abundance was associated with fertility in soil. Twenty five different spore species belonging to Acaulosporaceae (41.4 %), Glomeraceae (36.2 %), Ambisporaceae (13.6 %); Pacisporaceae (8.4 %) and Scutellosporaceae (0.3 %) families were identified at generic level. Spore abundance for a specific family was associated with soil properties and fertility. There was an interaction between soil site and spore family. Ambisporaceae spores were associated with low fertility and lightly soils, Glomeraceae with more fertile soils and disturbed ecosystems and the Acaulosporacea spores were associated with less disturbed soils of more natural ecosystems. The grasslands of Northern Tierra del Fuego showed a wide range of soil properties and fertility for plant growth that determine different vegetation types, growth forms and floristic composition of plant communities. This variation was mainly attributed to the long term grazing modalities and soil disturbances, and the distribution of AM fungal spores density and spores family were associated to these variables.