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.Keywords: leaf decay coefficients, decomposition, functional trophic groups, sandy coastal plain.Resumo: Objetivos: Avaliar a degradação foliar de Salix humboldtiana Willd. e a colonização pela comunidade de invertebrados aquáticos em um lago raso subtropical, planície costeira do Rio Grande do Sul, Brasil; Métodos: Bolsas de decomposição contendo 6,85 g de folhas foram incubadas na região litorânea, na superfície do sedimento, e retiradas após 1, 4, 7, 14, 32, 47 e 71 dias de decomposição; Resultados: Aos 71 dias foi registrada a degradação de 51% do peso inicial (k = 0,0100 d -1 ). O tempo estimado para a degradação de 95% do peso inicial dos detritos foi 300 dias. Foram identificados 16.040 organismos, distribuídos em 35 táxons. Caenidae (25,9%), Oligochaeta (19%), Ostracoda (13,8%), Hydracarina (9,8%), Tanypodinae (9,7%) e Coenagrionidae (7,7%) foram os táxons mais representativos. Foi observado incremento na riqueza, densidade e diversidade dos táxons ao longo do tempo, com tendência à estabilização dos valores de diversidade. Em relação aos grupos tróficos funcionais (GTFs), coletores-catadores representaram 57,6% da comunidade, enquanto predadores (25%), raspadores (15,8%), coletores-filtradores (0,88%) e fragmentadores (0,73%) também foram representados. A diversidade e homogeneidade dos GTFs apresentaram estabilização a partir do 14º dia; Conclusões: Os detritos de S. humboldtiana fornecem um habitat favorável por tempo suficiente para suportar ...

Benthic macroinvertebrates and degradation of phytomass as indicators of ecosystem functions in flooded rice cropping

“…However, for the conventional system, this diversity is smaller, and any variation is related to losses in the ecosystem function. Our results on degradation agree with those reported by Telöken et al (2011), which had greatest biomass losses in the initial phase, with a trend to stabilization that extends from the day 32 until the end of the experiment, at day 71. Abundance did not correlate with biomass decay in the systems, but it was significant for the natural wetland, showing that the benthic macroinvertebrates in cultivation areas were probably affected, having Table 3.…”

“…Using decomposition bags in a lentic environment, in the southern end of Rio Grande do Sul state, Telöken et al (2011) found a greater abundance of organisms than that found in the present study. However, despite the proximity of the sampled sites, this work was conducted in the winter, while Telöken et al (2011) performed theirs in the autumn with an average temperature of 23.95°C, which may have affected these differences, as well as the differences between the evaluated plant species (Carvalho & Uieda, 2009;Gimenes et al, 2010).…”

“…In the natural wetland, detritivores appeared in a greater proportion at the day 14; and, in the organic management, they appeared at the day 28, gradually increasing after this period. For Telöken et al (2011), despite the high correlation of shredders Values followed by equal letters, in the lines, show no significant difference, at 5% probability. The standard deviation is described in parentheses.…”

“…However, despite the proximity of the sampled sites, this work was conducted in the winter, while Telöken et al (2011) performed theirs in the autumn with an average temperature of 23.95°C, which may have affected these differences, as well as the differences between the evaluated plant species (Carvalho & Uieda, 2009;Gimenes et al, 2010).…”

“…Thus, the degradation process can provide important information on ecosystem functionality (Telöken et al, 2011), and can help in the definition of a sustainable management.…”