Leaf degradation of Salix humboldtiana Willd. (Salicaceae) and invertebrate colonization in a subtropical lake (Brazil)

Abstract

AIM: To evaluate leaf degradation and invertebrate colonization of Salix humboldtiana Willd. in a subtropical shallow lake on the coastal plain of Rio Grande do Sul, Brazil; METHODS: Litter bags containing 6.85 g of leaves were incubated in the superficial layer of sediment in the littoral region for 1, 4, 7, 14, 32, 47 and 71 days; RESULTS: After 71 days, a loss of 51% of the initial leaf weight was observed (k = 0.0100 d-1). We estimated that it would take 300 days to lose 95% of the initial weight. A total of 16040 organisms and 35 taxa were identified. Caenidae (25.9%), Oligochaeta (19%), Ostracoda (13.8%), Hydracarina (9.8%), Tanypodinae (9.7%) and Coenagrionidae (7.7%) were the most highly represented taxa. We observed increases in density, richness and diversity of taxa over time, with a stabilizing trend noted in the taxa diversity. Regarding the functional trophic groups (FTGs), gathering-collectors accounted for 57.6% of the community, while predators (25%), scrapers (15.8%), filtering-collectors (0.88%) and shredders (0.73%) were also represented. The diversity and evenness of the FTGs had stabilized by day 14; CONCLUSIONS: S. humboldtiana detritus provides a favorable habitat for a sufficient duration to support a high density and diversity of aquatic invertebrates. The small percentage of shredders indicates the minor influence of the invertebrate community on the rate of detrital degradation. The main contribution of invertebrates to detrital processing comes from the consumption of fine particulate organic matter by gathering-collectors.