Changes in plant cover induced by grazing affect the soluble fraction of soil organic carbon – but not the total pool size in the arid rangelands of Patagonian Monte, Argentina

Abstract

Soilis the largest organic C (SOC) pool in the biosphere. The size ofthis pool depends on the primary production and SOC residence time which arecontrolled by biome type, climatic conditions and land management.In arid ecosystems, these controls are stronglyrelated to the amount and seasonal distribution of precipitation. However, the low plant cover (< 40 %), the spatial heterogeneity ofplants, and the selectivity of grazing by domestic livestock may also influenceSOC dynamics and stability. Most changes in plantcommunities induced by grazing are not reversible after removal of thisdisturbance agent. Accordingly, our ability to predictand mitigate consequences of grazing disturbance on ecosystem function andglobal change depends, in part, on a better understanding of the effects ofvegetation changes on the size and composition of SOC pools. The objectives ofthis study were (i) to analyze whether theeffects of grazing pressure on plant canopy are reflected in the size and compositionof the SOC pool, and (ii) to identify easily measurable variablesrelated to SOC that could be used as indicators of changes in organic C poolsin grazed rangelands.