Grazing-induced changes in plant patch structure alter soil organic carbon quality in the arid rangelands of the Patagonian Monte, Argentina

Abstract

Plant patches are structural and functional units in arid ecosystems. Grazing leads to cover reduction of preferred perennial grasses and shrub encroachment with high soluble phenol (Ph) concentration in leaves. We asked whether the amount and chemical quality of soil organic C (SOC) are related to grazing-induced changes in patch canopies in arid rangelands of the Patagonian Monte. We selected five sites with increasing canopy signs of grazing disturbance. We recorded canopy attributes at five patches per site and assessed surface SOC and soil Ph concentrations with different structural complexity. Plant patches of the least disturbed sites had high shrub species richness and covers, high SOC and low soil Ph concentrations. In contrast, plant patches of the most disturbed site had the lowest shrub species richness and perennial grass cover, and high SOC and Ph concentration (total and low complex). Changes in patch canopy induced by grazing disturbance were not linearly related to changes in SOC concentration. Sites with the highest and the lowest grazing disturbance exhibited similar SOC concentrations, but different chemical composition (increased concentration of Ph in most disturbed sites). Resting from grazing may prevent the loss of plant diversity and avoid the increase in soil Ph concentration.