CONICET | Buscador de Institutos y Recursos Humanos

mationof stable organic matter and hence climate change mitigation. The structure, diversity and activity of soilmicrobial communities are influenced by the quantity and quality of organic compounds entering soils throughthe contribution of their root exudates and plant litter, which the microorganisms use as a substrate forbiosynthesis and energy source. However, grazing effect on the soil microorganisms showed variable resultsdependent on the ecosystem under study. One of the main challenges of this millennium is the sustainability ofagricultural production, especially in fragile soils such as those present in Patagonia. Therefore, our objectivewas to evaluate the responses of microbial biomass carbon (MBC), soil basal respiration (SBR), the derived coefficientsand the abundance of fungi and bacteria under contrasting long-term grazing intensities in an environmentalgradient. The study was established in three ecological areas Mata Negra Thicket (MNT), DryMagellanic Steppe (DMS) and Humid Magellanic Steppe (HMS) with two grazing intensities. Soil samples weretaken over two years in different seasons (autumn, winter, spring and summer). Results showed that biotic and abiotic factors (temperature and precipitation), plant communities and soil characteristics modulated the microbial structure and function in ecological area. On the other hand, high grazing intensity decreased the MBC and microbial coefficient (qM). There was a seasonal and interannual dynamic in the MBC and the bacteria and fungal communities, attributed mainly to temperature and precipitation. The results indicated that the effect ofgrazing intensity in soil microbial communities depends largely on intrinsic characteristics of each ecological area defined by the environmental gradient.