The effects of abiotic variables on detritus decomposition in Brazilian subtropical mangroves

Renan De Souza Rezende,José Francisco Gonçalves Jr,Marcelo De Oliveira Pinto,Mauricio Mello Petrucio

doi:10.1590/s2179-975x2013000200007

Renan De Souza Rezende, José Francisco Gonçalves Jr + Show 2 more

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https://doi.org/10.1590/s2179-975x2013000200007

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Abstract

AIM: The objective of this study was to determine the rate of decomposition of two dominant arboreal species (Rhizophora mangle and Avicennia schaueriana) in two Brazilian subtropical mangroves (Ratones and Itacorubi) and their relationship with abiotic factors during two periods of the year (winter and summer). METHODS: Senescent leaves (4 ± 0.1 g dry weight) were placed into litter bags (20 × 25 cm with 1 cm mesh size) and submersed in mangrove forests during a winter and a summer sampling period. Replicates (n = 4) of each detritus sample were obtained from the mangroves after 7, 15, 30, 60, 90 and 120 days of incubation during both time periods. During each period, in situ measurements were taken to obtain the temperature, electrical conductivity, pH, and dissolved oxygen in the water column. RESULTS: The species R. mangle and A. schaueriana exhibited slow rates of decomposition at Itacorubi and intermediate rates at Ratones during the winter, while quick rates were observed at both sites during the summer; this result suggested that water temperature is an influential factor. There was no difference in the loss of mass between the sites during the winter, but in the summer, the highest values were observed for R. mangle in Ratones site. The highest summer temperatures were negatively associated with mass loss, suggesting that the temperature is an influential factor. During the winter, remaining mass was associated negatively with electrical conductivity, possibly because of a greater resource available to decomposing communities, and it was also positively associated with oxygen, revealing a pattern opposite to that observed in the literature. CONCLUSIONS: Our results showed that decomposition accelerated with higher temperatures and that electrical conductivity decelerated with increased dissolved oxygen, confirming the effects of abiotic factors on both detritus decomposition and mangrove functioning.

Highlights

Mangroves are coastal ecosystems that serve as a transition between sea and land, and they are present in tropical and subtropical regions in areas that are subject to tide regimes (Ong, 1995; Silva et al, 2005)
The present study aims to determine the leaf-breakdown rate of two arboreal species (Rhizophora mangle Linnaeus and Avicennia schaueriana Stapf and Leechm. ex Moldenke) in two subtropical mangroves and their relationship with water temperature, electrical conductivity and dissolved oxygen during the winter and summer
The water temperature, pH and dissolved oxygen values did not differ between the Itacorubi and Ratones mangroves during the two sampling periods

Summary

Introduction

Mangroves are coastal ecosystems that serve as a transition between sea and land, and they are present in tropical and subtropical regions in areas that are subject to tide regimes (Ong, 1995; Silva et al, 2005). The allochthonous leaf litter decomposition process directly affects the release of nutrients into the environment, liberating them back to the trophic cascades (Fernandes, 2003; Gonçalves Junior et al, 2012b). This leaf breakdown causes the carbon in the biomass that is incorporated from photosynthesis to return to the atmosphere as CO2, where part of it, along with other minerals, is available to and reincorporated by plants and other organisms (Shafer and Roberts, 2007; Gonçalves Junior et al, 2012b)

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