How does soil particulate organic carbon respond to grazing intensity in permanent grasslands?

Abstract

Modification in grazing intensity causes functional changes in permanent grasslands, e.g. in carbon (C) cycling. However, we still know little about how the soil organic C of permanent grasslands responds to grazing intensity. In a grassland experiment with three levels of grazing intensity, we monitored root and rhizome C stocks, particulate organic C stocks, total soil C stocks, above-ground net primary production and plant species groups abundance over 7 years. A simple model was used to estimate the mortality of roots and rhizomes, decomposition rates of particulate organic C, and C fluxes under different grazing intensities. After 7 years, low grazing intensity and no grazing led to a modification in above-ground vegetation (production, plant species composition, nitrogen content) and a reduction in C transferred between roots and particulate organic matter fractions, while the C stocks of root and rhizomes, particulate organic matter and total soil were not significantly affected by grazing intensity. However, particulate organic C showed a strong interannual variability. Particulate organic C could have reacted more slowly than expected to changes in grazing intensity, or a marked interannual variability of particulate organic C stocks, through an increase in decomposition rates in all the grazing treatments, could have slowed down the accumulation of particulate organic C and masked the effect of the grazing intensity treatments.