Controles extrínsecos e intrínsecos en la descomposición de hojas de tres especies de árboles pioneros comunes en quebradas de bajo orden en los Andes Centrales de Colombia

Abstract

ABSTRACT Riparian forests provide high amounts of leaf litter to tropical headwater streams (1–3 order) and its decomposition is controlled by interactions between leaf quality and macroinvertebrate activity. However, few studies have been conducted in North Andean streams. We conducted a leaf litter decomposition experiment using three native tree species (Heliocarpus americanus, Nectandra sp., and Cecropia telealba) in two headwater streams in the Colombian Coffee-growing Eco-Region. The interactive roles of intrinsic factors (quality) and extrinsic factors (presence/absence of macroinvertebrates) on decomposition rates were tested. Three single-species treatments, a species-mixture treatment, and an artificial substrate treatment were incubated in either coarse-pore mesh or fine-pore mesh bags to allow or exclude macroinvertebrate colonization, respectively. Bags were removed from the streams 7, 14, 28 and 56 days after starting the study. Toughness and chemical quality of senescent leaves of each species were determined in order to test their effect on the decomposition rates. The k-values for the three single-species and the species-mixture treatments indicated that decomposition occurred at medium to fast rates (0.009–0.01 day−1). H. americanus showed the greatest mass loss at the end of the trial, followed by C. telealba and Nectandra sp. Leaf toughness was positively correlated with carbon-to-nitrogen ratio (C: N) and carbon-to-phosphorus ratio (C: P) and, in turn, the three characteristics were negatively correlated with breakdown rate. A total of 3876 individuals from 13 orders, 35 families, and 47 genera colonized leaf-litter bags. Chironomidae, Lumbriculidae, and Hydropsychidae were the families with the highest abundance. The abundance and richness of macroinvertebrates in the leaf-litter bags showed no correlation with the descriptors of intrinsic characteristics (leaf quality). These results indicate that among the three tree-species in the study, the intrinsic characteristics of senescent leaves determine their mass loss rates, while the macroinvertebrate abundance or richness play a secondary role, probably due to the fact that shredders were not abundant.