Leaf breakdown and invertebrate colonization of Eucalyptus grandis (Myrtaceae) and Hirtella glandulosa (Chrysobalanaceae) in two Neotropical lakes

Abstract

Aim: This study compared the leaf breakdown of Eucalyptus grandis Hill ex. Maiden (an exotic species) and Hyrtella glandulosa Spreng. (a native species), in order to assess the role of invertebrates in decomposition in two tropical lakes (Aguape and Barra) of the Rio Doce State Park in Southeast Brazil, receiving allochthonous organic matter during the dry and rainy seasons; Methods: Senescent leaves (4 ± 0.1 g dry weight) were placed in litter bags (30 × 30 cm, 5 mm mesh size) and submerged in the lakes. Replicate bags (n = 4) were then retrieved after 3, 7, 15, 30, 60, 90 and 120 days; Results: The breakdown of E. grandis leaves (range k = –0.007 to –0.015) was faster than H. glandulosa (range k = –0.005 to –0.008). Breakdown rates were higher during the rainy season than the dry season. Leaves of E. grandis and H. glandulosa did not differ in terms of invertebrate colonization. The highest densities were observed in Aguape Lake during the rainy season. Taxonomic richness was higher in E. grandis and in Aguape Lake, but no differences between the rainy and dry seasons were observed. Functional trophic groups differed between leaf types and seasons. Gatherer-collectors and scrapers predominated in E. grandis and in the dry season; Conclusions: The higher breakdown observed in Barra Lake was probably a consequence of the elevated temperatures and the presence of Gastropoda (scrapers). Aquatic invertebrates did not have difficulties in the colonization of exotic leaves (E. grandis) compared with native leaves (H. glandulosa). We observed that in the rainy season, the higher decay rates and density of invertebrate communities, indicating the increased temperatures, nutrient inflow and organic matter brought by the rain, accelerated this process compared with the dry season.