Riparian cover buffers the effects of abiotic and biotic predictors of leaf decomposition in subtropical streams

Stream functioning is energetically dependent on terrestrial vegetation due to the input of leaves. The decomposition process of this allochthonous resource may be controlled by leaf identity and abiotic and biological predictors that are also influenced by the presence of riparian cover. In subtropical Uruguayan streams, most of the riparian zones have been reduced, and the response of the decomposition process to the predictors may depend on the presence of riparian cover. We analyzed the importance of leaf identity and riparian cover on the abiotic and biotic predictors of leaf decomposition in rangeland streams, comparing two stream types (open canopy stream, OCS, and riparian forest stream, RFS). Decomposition experiments of native species (Eryngium pandanifolium and Schoenoplectus californicus) and the exotic Eucalyptus globulus were carried out. There were no significant differences in decomposition rate between the stream types; however, some predictors had significant, albeit differential, effects on the decomposition process depending on the presence of riparian forest. In OCS, the decomposition rates were positively influenced by NH₄-N and streamflow but negatively by PO₄-P, conductivity, and proportions of scrapers. Most of these variables had nonsignificant effects on decomposition rates in RFS. Experimentation procedures are needed to establish the mechanisms by which the presence of riparian cover modulates the response of the leaf decomposition to the effects of abiotic and biotic variables in subtropical streams. Leaf decomposition is much more affected by changes in leaf identity, suggesting that riparian changes that are accompanied by changes in leaf inputs may strongly affect this ecosystem function.