Litter decomposition in water limited ecosystems and under grazing in N Patagonia.

CARRERA, A.L.; BERTILLER, M.B; SAIN, C.L.; LARREGUY, C.; VARGAS, D.N.

Mérida, Mexico.

Congreso; Ecology in an Era of Globalization; 2006

The Ecological Society of America.

Grazing promotes changes in the species composition of plant communities and consequently this could modify the quantity and the quality of litter that they produce. We hypothesized that the replacement of plant species induced by grazing increases the relative contribution of shrubs to the total litter, altering the chemical composition and the decomposition rates of the litter. In two contrasting vegetation conditions (areas excluded from sheep grazing and grazed by sheep) characteristic of the shrubland of Larrea divaricata and Stipa spp., we randomly collected aerial litter and fine roots (, 2 mm of diameter). We assessed the initial concentrations of nitrogen, total phenolics and lignin in the collected samples and then we constructed litterbags which were randomly placed in the field to evaluate the monthly in situ dry mass loss throughout a year. In the non-grazed area, perennial grasses contributed with 73% of aerial litter and shrubs provided the rest, whereas, we found the reverse (22% of grasses and the rest of shrubs) in the grazed area. Aerial litter and fine roots of the grazed area showed the highest initial concentration of total phenolics and lignin. Also, nitrogen concentration was higher in aerial litter of the grazed area than in that of the non-grazed area. We did not find significant differences in nitrogen concentration of fine roots between both areas. The annual dry mass loss produced by decomposition differed significantly between the areas and it was 30,75 % and 22,02% in the aerial litter of the non-grazed and grazed area, respectively; whereas, dry mass loss of fine roots was 23,53% and 16,42 % in the non-grazed and grazed area, respectively. Our results emphasize the importance of the specific composition and chemical characteristics of the litter on decomposition processes of the organic matter and probably on nutrient cycling in the ecosystem.