Soil parameters and host plants associated with arbuscular mycorrhizae in the grazed Magellanic steppe of Tierra del Fuego

Association between soil properties and two host plants for arbuscular mycorrhizal fungi in a field study involving grasslands exhibiting a range of degradation as a result of long-term modes of sheep grazing in Tierra del Fuego (Argentina) was researched. Vegetation rich in prostrate shrubs (Empetrum rubrum) of little forage value that grow in soils of low pH, high carbon, low N, and low Ca + Mg were associated with selective long-term grazing at high intensity. Vegetation with large proportions of mycorrhizal grasses such as Poa rigidifolia and Deschampsia flexuosa, which species grow in soil of less acidity, low carbon/nitrogen ratio, high NO3− and high exchangeable Ca + Mg, were associated with selective grazing at moderate intensities or nonselective grazing at high intensity in short term. These two grasses, representing more palatable and nutritious plants for sheep, were present at different degrees of coverage and AM-spore densities in their rhizospheric soils. Twenty-five species of AM-fungal spores belonging to the Acaulosporaceae (41.4%), Glomeraceae (36.2%), Ambisporaceae (13.6%), Pacisporaceae (8.4%), and Scutellosporaceae (0.4%) were identified. Ambisporaceae spores were associated with low fertility and light soils, Glomeraceae spores with more fertile soils and disturbed ecosystems, and Acaulosporacea spores with less disturbed ecosystems. Our results indicated that the sheep-grazing mode and intensity affected vegetation and soil fertility in grasslands. AM-fungal population in rhizopheric soils of palatable grasses would thus provide an indicator of grassland degradation and fertility.

▶ Long-term sheep grazing mode was associated with soil fertility and the growth form of the plant community. ▶ AM spore density and taxa were associated with the fertility of the soil. ▶ Ambisporaceae spores were more abundant in soil of low fertility, Glomeraceae in more fertile soils and disturbed ecosystems, and Acaulosporacea with less disturbed ecosystems.