Leaf traits of Brazilian semiarid species as regulatory factors for associated aquatic invertebrates

Semiarid leaf species and colonization by aquatic invertebrates

The input of leaf litter is an important energy source for the riparian vegetation of aquatic ecosystems, and the chemical composition of leaf litter is decisive for colonization by invertebrates in streams. Plant species of the semiarid regions present different morphophysiological characteristics to combat the effects of drought, including tough leaves that have less nutritional quality. However, although concern regarding the decomposition of organic matter in aquatic ecosystems in semiarid regions is increasing, no information exists on the influence of leaf traits (e.g., N, C:N ratio and toughness) before the colonization of invertebrates and the decomposition of leaf litter. We hypothesized that: i) leaves with greater toughness, higher C:N ratio and lower amount of N present low density and biomass of associated invertebrates; ii) greater density and biomass of associated invertebrates results in increased decomposition rates; and iii) leaf traits influences the structure and composition of functional feeding groups of associated invertebrates. We incubated senescent leaves of Tabebuia aurea and Aspidosperma pyrifolium in a Brazilian semiarid stream using litter bags, and after 3, 7, 15 and 30 days, four litter bags were withdrawn for laboratory washing of the remaining leaf sediment and for collection of associated invertebrates. A. pyrifolium leaves presented higher nutritional quality (low C:N ratio, lower toughness), and the decomposition rate was higher than T. aurea leaves. Invertebrate density and biomass varied among litter, being higher in T. aurea and A. pyrifolium, respectively. The leaf litter quality also altered the composition of functional feeding groups. We observed a higher density of filters on T. aurea and collectors on A. pyrifolium. Both T. aurea and A. pyrifolium presented higher biomass of collectors, however T. aurea showed higher biomass of filters than A. pyrifolium. In the absence of shredders, leaf litter may have been used by invertebrates as a substrate, for shelter against predators and current, and sporadically as a food resource. Thus, differences in the leaf traits were important structures of the streams invertebrate. These are the first results of the influence of leaf traits on invertebrate colonization in the streams of semiarid regions, and reinforce the need for studies to verify the contribution of organic matter as well as the feeding preferences of invertebrates.