INVESTIGADORES
MORETTO alicia Susana
artículos
Título:
Litter quality and nutrient cycling affected by grazing-induced species replacements along a precipitation gradient.
Autor/es:
M. SEMMARTIN, ; M.AGUIAR, ; R. DISTEL, ; A. MORETTO; C. GHERSA
Revista:
OIKOS
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Lugar: Londres; Año: 2004 vol. 107 p. 148 - 160
ISSN:
0030-1299
Resumen:
One of the potential mechanisms for the impact of herbivores on nutrient cycling is the
effect of selective grazing on litter quality through changes in species composition.
However, the scarce evidence collected on this mechanism is controversial and
seemingly influenced by site-specific variables. In this paper, we explored the
consequences of grazing-induced changes in species composition on litter quality and
nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall
gradient, we selected species promoted and diminished by grazing from three natural
rangelands of Argentina, analyzed their litter quality, and determined their
decomposition and nutrient release kinetics under common greenhouse conditions.
Litter quality and decomposition rates were strongly associated with plant response to
grazing. However, the magnitude and direction of these differences depended on the
ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had
higher nitrogen and phosphorus contents, faster decomposition rates, and higher
release of nitrogen to the soil than species diminished by grazing (C3and C4grasses). In
the intermediate and dry sites, species promoted by grazing had lower nitrogen and
phosphorus contents, and slower decomposition rates than those diminished by grazing
(C3 grasses in both cases). Decomposition of the entire group of species was not
correlated with mean annual rainfall, but when litter of the species diminished by
grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was
immobilized more often than mineralized, even after one year of incubation.
Immobilization was negatively correlated with precipitation. All these results indicate
that grazing may significantly alter nutrient cycling by affecting litter quality through
changes in species composition. These effects seem to be larger when species
replacements induced by grazing either involve functional groups, as it was the case
in our wettest site, or change root to shoot ratios. Therefore, the functional groups
involved in the replacement of species as well as shifts between belowground and
aboveground allocation should play a key role in grazing-induced changes on nitrogen
cycling.