Abstract

BIASI, Cristiane; CEREZER, Cristina  and  SANTOS, Sandro. Biological colonization and leaf decomposition in a subtropical stream. Ecol. austral [online]. 2016, vol.26, n.2, pp.189-199. ISSN 1667-782X.

In small streams, aquatic community obtains energy mainly from leaves of the riparian vegetation. Processing these leaves involves physical, chemical and biological factors that may difer among leaf species. We assessed the efects of litter quality on leaf decomposition and colonization by aquatic invertebrates in a subtropical stream. Leaves from two native, highly represented tree species common in subtropical riparian areas, Ficus luschnathiana and Gasearía sylvestris, were incubated in coarse mesh bags in a stream. Bags were sampled weekly during an incubation of 28 days. The decomposition rates were higher in leaves of F. luschnathiana than in those of C. sylvestris. In the frst seven days of the experiment, leaves of F. luschnathiana lost ~60% of the initial mass, while Cascarla sylvestris lost around 30%. The leaves of C. sylvestris were initially more palatable than the leaves of F. luschnathiana, perhaps due to their lower lignin and cellulose content, and lignin to N ratio (Lignin:N). These structural compounds enhance leaf toughness thereby protecting them from herbivores and detritivores. However, leaves of F. luschnathiana were comparatively softer, which apparently facilitated fungal colonization and conditioning. Thus, leaves of F. luschnathiana attained high shredders density, which was refected in a higher leaf mass loss. Our results suggest that litter decomposition was sensitive to fungal biomass and leaf toughness. We observed that microbial conditioning, rather than the initial chemical quality of the leaf litter, decreased leaf toughness thereby stimulating further colonization by shredders and enhancing the decomposition process. The fungal community has a key-role in the degradation process within aquatic environments, breaking down even low-quality litter (i.e., F. luschnathiana) and promoting changes in the composition and structure of the invertebrate community.

Keywords : Shredders; Chironomidae; Leaf-toughness; Fungal biomass.