Leaf litter decomposition and macroinvertebrate assemblages in a tropical Andean stream (Ibague, Colombia)

The ecosystem functioning in headwater Colombian Andean streams is still poorly understood. The objective of this study was to evaluate the leaf decomposition of alder (Alnus acuminata), sietecueros (Andesanthus lepidotus) and a 1:1 mixture of the two species using coarse-(5 mm) and fine-mesh litter bags (0.5 mm) in the Las Perlas stream, a high-altitude tropical Andean aquatic system (2390 m.a.s.l.). A subset of 4-litterbags of each treatment was retrieved at 3, 7, 15, 20, and 30 days and analyzed for litter decomposition and invertebrate colonization (density, functional feeding groups-FFG). Decomposition rates (k) were significantly distinct between treatments and over the experiment: A. acuminata (62 % leaf dry mass loss) > Mixture (53 %) > A. lepidotus (31 %), mainly during the first week and toward the final phase of the study. The highest k-value was registered in A. acuminata (- 0.019 days-1) and was lower in A. lepidotus (- 0.004 days-1). Macroinvertebrate density tended to increase over the incubation period, was higher in the day 20, and was primarily dominated by Diptera (Chironomidae, Simuliidae), Trichoptera (Hydroptilidae), Coleoptera (Elmidae), and Ephemeroptera (Leptohyphidae), whereas the collectors predominated, attaining higher values in the Mixture than in the species alone. Overall, our results slightly suggest that invertebrate colonization and their function are related to the leaflitter diversity and mixing, which can define the dynamics of the decomposition and nutrients in tropical high-Andean aquatic systems.