Controles extrinsecos e intrinsecos en la descomposicion de hojas de tres especies de arboles pioneros comunes en quebradas de bajo orden en los Andes Centrales de Colombia

Resumen Los bosques riberenos aportan grandes cantidades de hojarasca a las corrientes tropicales de bajo orden (1-3) y su descomposicion esta controlada por las interacciones entre la calidad de la hoja y la actividad de macroinvertebrados. Sin embargo, se han realizado pocos estudios en quebradas del norte de los Andes. Llevamos a cabo un experimento de descomposicion de la hojarasca en el que se utilizaron tres especies de arboles nativos (Heliocarpus americanus, Nectandra sp. y Cecropia telealba) en dos arroyos de cabecera en la Eco-Region Cafetera de Colombia. Se probaron las funciones interactivas de los factores intrinsecos (calidad) y los factores extrinsecos (presencia/ausencia de macroinvertebrados) en las tasas de descomposicion. Tres tratamientos de una sola especie, un tratamiento de mezcla de especies y un tratamiento de sustrato artificial se incubaron en bolsas de malla de poro grueso y malla de poro fino. Se retiraron las bolsas de las corrientes 7, 14, 28 y 56 dias despues de comenzar el estudio. La dureza y la calidad quimica de las hojas senescentes de cada especie se determinaron para probar su efecto sobre las tasas de descomposicion. Los valores de k para las tres especies individuales y la mezcla de especies indicaron que la descomposicion se produjo a tasas medias a rapidas (0.009-0.01 dia(-1)). H. americanus mostro la mayor perdida de masa, seguido de C. telealba y Nectandra sp. La dureza se correlaciono positivamente con la relacion carbono-nitrogeno (C: N) y la relacion carbono-fosforo (C: P) y, a su vez, las tres caracteristicas se correlacionaron negativamente con la velocidad de descomposicion. Un total de 3876 macroinvertebrados de 13 ordenes, 35 familias y 47 generos colonizaron los paquetes de hojas. Chironomidae, Lumbriculidae e Hydropsychidae fueron las familias con mayor abundancia. La abundancia y riqueza de macroinvertebrados en las bolsas de hojarasca no mostro correlacion significativa con los descriptores de las caracteristicas intrinsecas (calidad de la hoja). Los resultados indican que las caracteristicas intrinsecas de las hojas determinan sus tasas de perdida de masa, mientras que la abundancia o riqueza de macroinvertebrados juegan un papel secundario, probablemente por su baja abundancia. 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.

Automated summary

The study shows that the intrinsic characteristics of leaves determine their decomposition rates, while the abundance or richness of macroinvertebrates play a secondary role.