Relationships between cattle grazing, soil microbiology and nutrients cycle in highland pastures

Highland pastures are particular agro-ecosystems with a high level of plant and animal biodiversity, and for this reason semi-natural grassland are classified as High Nature Value Farmland. This study aims at characterizing the agroecological relationships among grazing animals-plants-microorganisms in alpine summer pastures. The study area included two summer farms in the Dolomites, Eastern Italian Alps. Both summer farms were located at an elevation around 2,000 m asl, and were grazed by dairy cows from mid-June to mid-September. In order to assess the impact of dairy cattle grazing on the functional microbial biodiversity, surveys were carried out using topsoil cores before (‘point zero’) and during the grazing period. The distribution of cattle stocking rate at temporal and spatial scale was analysed by using GPS tracking of grazing animals and farmer’s interviews. The samples of soils were collected in patches representative of different vegetation types and stocking rates, with three repetitions for each sampling points. A molecular ecological approach was applied, analysing microbial communities in terms of abundances relative to copies of target genes through the application of real-time PCR. The studied genes were nosZ for denitrification, amoA archea and bacteria for nitrification. The analysis highlighted different outcomes between the considered areas, showing a likely impact of grazing on microbial communities but in different terms depending on the local pedoclimatic and vegetational conditions and on the cattle stocking rates. This kind of approach will be integrated with indicators on carbon sink, in order to have an in-depth view of the ecosystem support services, such as nutrient cycle and soil formation regulation, carbon storage and supply in soil, and forage production. These preliminary results could be used to develop specific and minimally-invasive biophysical indicators of supporting (and regulating) ecosystem services. These tools will assist the definition of strategies aiming at enhancing the sustainability of grazing livestock systems in compliance to agroecology principles.