Spatial patterns and chemical characteristics of root biomass in ecosystems of the Patagonian Monte disturbed by grazing

We hypothesized that the reduction in perennial-grass cover induced by grazing in shrublands would be associated with a reduction in fine-root biomass in the upper soil, an increase in the spatial heterogeneity of root biomass, and an increase in N and total phenolics concentrations in fine-root biomass. We analysed the spatial distribution of fine-, intermediate-, and thick-root biomass and the N and total phenolics concentrations in fine roots in sites with different aboveground-plant cover induced by grazing disturbance in the Patagonian Monte. We selected sampling sites varying in the distance to the watering point, the time since sheep grazing exclusion, and historical sheep stocking rates/paddock characteristics. Sites excluded from grazing and those far to the watering point showed the highest perennial-grass cover. Tall- and dwarf-shrub cover did not differ among sites. Fine-, intermediate-, and thick-root biomass and the chemistry of fine roots did not strongly differ among sites. At all sites, N concentration in fine roots was similar to that measured in tall shrubs while total phenolics concentration in fine roots fell within the range of that assessed for perennial grasses and tall shrubs. Results on N concentration would indicate that fine roots of tall shrubs are a main component of the bulk fine-root pool supporting previous evidence that life form shifts resulting from grazing has little effect on the root biomass and chemistry in the upper soil of rangelands.