Effect of Phylloicus on leaf breakdown in a subtropical stream

EnglishShredder invertebrates are key organisms in the decomposition of leaves in streams. These organisms transform coarse organic matter into fine organic matter, incorporate carbon and nutrients into animal biomass and promote the recycling of terrestrial carbon. Despite their importance in headwater streams, the life history of this shredder taxa and their relationship with organic matter processing is unclear. The main objectives of this study were to evaluate leaf breakdown during two periods of the year and test whether differences in the Phylloicus larvae abundance alter organic matter processing. We incubated leaves of a common native species (Campomanesia xanthocarpa) in the same stream during March (autumn) and October (spring). Samples were collected after 7, 15 and 30 days. After 30 days of incubation, the remaining leaf mass was lower in autumn (30%) than in spring (53%). The breakdown rate (k) was –0.0449±0.0042 day–1 in autumn and –0.0180± 0.0003 day–1 in spring. The abundance of Phylloicus was also higher in autumn than in spring (11.1 ± 1.9 ind/litter bag versus 2.7 ±1.9 ind/litter bag). We observed a positive correlation between Phylloicus abundance and leaf mass loss in autumn (r = 0.74). Our results demonstrate that Phylloicus abundance differs with season and impacts the processing of particulate organic matter. Furthermore, this work highlights the importance of Phylloicuslarvae and their contribution to leaf breakdown in subtropical streams. portuguesInvertebrados fragmentadores sao organismos chave para a decomposicao de detritos foliares em riachos. Estes organismos transformam a materia orgânica particulada grossa em materia orgânica particulada fina e incorporam carbono e nutrientes em biomassa animal. Apesar de sua importância em riachos de cabeceira, a historia de vida desse taxon fragmentador e sua relacao com o processamento de materia orgânica e incerta. O principal objetivo deste estudo foi avaliar a decomposicao de detritos foliares em dois periodos do ano, a fim de testar se diferencas na abundância de larvas Phylloicus alteram o processamento dos detritos. Folhas senescentes de uma especie nativa (Campomanesia xanthocarpa) foram incubadas em um riacho nos meses de Marco (outono) e Outubro (primavera). Apos 7, 15 e 30 dias de experimento foram coletadas amostras para analise. Ao termino do experimento (apos 30 dias), a massa remanescente das folhas foi menor no outono (30%) do que na primavera (53%). O coeficiente de decomposicao foi de k = –0.0449± 0.0042 dia–1 no outono e de k = –0.0180± 0.0003 dia–1 na primavera. A abundância de Phylloicusfoi maior no outono quando comparada a primavera (11.1 ±1.9 ind/litter bag e 2.7 ±1.9 ind/litter bag, respectivamente). Observamos uma correlacao positiva entre a abundância de Phylloicus e a perda de massa dos detritos foliares no outono (r = 0.74). A abundância de Phylloicus variou entre as duas estacoes estudadas, o que esteve relacionado com o processamento dos detritos foliares. Nossos resultados tambem indicaram a importância das larvas de Phylloicus e sua contribuicao para a decomposicao foliar em riachos subtropicais.