Does decomposition of standard materials differ among grassland patches maintained by livestock?

VAIERETTI, MARÍA VICTORIA; CINGOLANI, ANA MARÍA; PÉREZ HARGUINDEGUY, NATALIA; GURVICH, DIEGO EZEQUIEL; CABIDO, MARCELO RUBÉN

AUSTRAL ECOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 vol. 35 p. 935 - 943

1442-9985

Grazing can modify vegetation structure and species composition through selective consumption, modifying plant litter quality and hence decomposability. In most grasslands, moderate stocking rates maintain a mosaic of high quality patches, preferentially used by herbivores (“grazing lawns”), and low quality tall patches, which are avoided. In grazing lawns decomposition rates can be accelerated because of a better litter quality and besides, due to the indirect effect of increased nutrient availability in soil. We aimed at testing this indirect effect using standard materials, comparing their decomposition in grazing lawns, open and closed tall tussock grasslands. We selected 10 patches of each type and sampled floristic composition, soil variables and cattle dung deposition. Standard materials were filter paper and Poa stuckertii litter. We prepared litterbags of 0.3 mm (thin mesh) and 1 mm mesh size (coarse mesh). Samples were incubated in two ways: aboveground (thin and coarse mesh) and belowground (only thin mesh) to analyse the conditions for decomposition on surface litter and buried litter-dead roots respectively, during 65 days. Physical and chemical soil variables did not differ among patch types, despite the large differences in species composition. Closed tussock grasslands showed the lowest dung deposition, confirming the differential use of the patch types. Soil nutrients availability (N-NO3-  and N-NH4+) were not significantly different among patch types. The standard materials followed different decomposition patterns across patch types. For aboveground incubated samples, Poa litter decomposed significantly faster in lawns, and lower in open tussock grasslands. In turn, filter paper decomposed significantly faster in closed tussock grasslands than in the other two patch types. Decomposition of belowground incubated samples did not significantly differ among patches, which suggest an homogeneous belowground environment, coincidently with the results of soil variables. Aboveground differences in decompostion may be associated to microclimatic conditions as result of vegetation structure.