Detritus production of aboveground macrophytes in a salt marsh in the Patos Lagoon estuary: decomposition rates and microbial dynamics

Abstract

In this study the microbial decomposition rates of three aboveground macrophytes (Spartina alterniflora, Spartina densiflora e Scirpus maritimus) were determined in a salt marsh at the Patos Lagoon estuary, by means of the litter bags method. The bacterial nitrogen and carbon standing crops on detritus were estimated, as well as the flagellate and fungal abundance during the decomposition process. The highest decay rate within 180 days was found for S. alterniflora material (73,43% of the original dry weight) and the lowest decay rate was obtained in the S. densiflora material (49,25% of the original dry weight). Spartina alterniflora and Scirpus maritimus debris showed comparable decay rates probably due to the similar morphological features of their leaves. During this study, trophic interactions were observed among bacteria and flagellates during decomposition of plant fragments. However, the addition of bacterial nitrogen and carbon to plants detritus was not significant. Microbial nitrogen content varied from 0.31% in Scirpus maritimus to 1.27% in S. alterniflora of detritus weight. Moreover, microbial carbon content varied from 0.1% in S. maritimus to 0.3% in S. alterniflora of detritus weight. Greater abundance of fungal mass (spores and hyphae) was observed between the 7th and the 90th day of the experimental period, probably contributing to the highest particulate nitrogen content found in the detritus of this plant during the same period.