Influence of land management on soil organic matter pools, plant traits and enzymatic activity in mountain grasslands

Mountain grasslands are globally widespread ecosystems which play a pivotal role in several provisioning, regulating, supporting and cultural ecosystem services. Often shaped over centuries by traditional agricultural activities, including mowing and livestock grazing, mountain grasslands are integral to both ecological function and local livelihood. This study investigated the impact of light grazing on the soil-plant system in extensively managed grasslands, with a focus on functional structure and soil-associated ecosystem functions, including soil organic carbon accrual. Five meadows and five pastures were identified in the Central Italian Alps to simulate land-use intensification along an elevational gradient. Both plant compartment and topsoil samples were collected from each site and characterized. Grazed sites showed higher organic carbon, total nitrogen, and available phosphorus contents as well as higher urease activity, resulting in a higher soil organic matter accrual compared to meadows. In contrast, meadows were characterised by higher fluorescein diacetate hydrolase and phosphomonoesterase activities as well as by greater plant biomass and specific leaf area values. The mineral-associated organic matter (MAOM) fraction was the main carbon and nitrogen pool, especially in meadows. Correlations found between MAOM features and plant traits/soil enzymatic activities suggest that MAOM, in both management systems, is not exclusively of microbial origin, but also influenced by the plant component. Finally, particulate organic matter and MAOM showed a different stability both within and between management systems. These findings underscore the importance of a sustainable grassland management in storing organic matter, thus contributing to climate change mitigation, as well as to enhance nutrient cycling and ecosystem health.