Spatial patterns of shallow-root biomass in grazed ecosystems of the southern Monte, Argentina

RODRIGUEZ, M.V; BERTILLER, M.B; SAIN, C.L

Mérida-México

Congreso; Ecology in an Era of Globalization; 2006

The Ecological Society of America

In arid ecosystems, grazing modifies the proportion of woody and non-woody plants in the canopy. These changes could affect the structure of the root system with consequences on the resource acquisition and nutrient cycling. We evaluated the spatial structure (horizontal and vertical) and the chemical composition (N and polyphenols concentrations) of fine root biomass (<1.4 mm) of the dominant plant community (i) in two replicates of three sites with different grazing intensity in the Southern Monte (without grazing, low grazing and high grazing) and (ii) in plots with dominant shrubs (Larrea divaricata) and grasses (Stipa tenuis) growing isolated and together. Grazing did not affect the spatial patterning and the chemical composition (N and polyphenols concentrations) of root biomass of the community. The concentration of polyphenols  in the root biomass of the community did not differ from that assessed in the dominant shrub and grass species while the N concentration was significantly lower than in dominant grasses. We did not find significant differences in the fine-root biomass and its spatial pattern between grasses and shrubs growing isolated or together. These results suggest that (i) fine roots of shrubs dominate in all sampled sites independently of the grazing intensity, (ii) shrubs developed a shallow opportunistic root system able to exploit an eventual increment in soil resources due to the reduction of grass-root biomass, (iii) grass roots were also able to occupy freed soil spaces, and (iv) grazing did not affect the chemical composition of root biomass and consequently would not affect the role of fine roots in the nutrient cycling.