Determinação da taxa de decomposição de folhas de espécies de mangue São Caetano de Odivelas-Pa

Abstract

Knowledge of the rate of decomposition of plant species is an important parameter to be considered in the cycling of mineral nutrients in any ecosystem. Depending on the speed of decomposition there is the formation of organic matter, essential for maintaining life and the balance of ecosystems, the retention of plant nutrient cations and the release of nutrients such as nitrogen, phosphorus, sulfur, boron among others for plants, thus influencing the cation exchange capacity, the chelating action of metal ions protecting them from insolubilization and buffering power. This work aims to investigate the decomposition rates of leaves from different mangrove species. The experiment was set up in the field in the region of São Caetano de Odivelas during the wet weather season. In the leaf samples the dry weight decay rate was determined. In the sediment samples: pH, eH and salinity. Of the species studied, Avicennia sp. decomposed more rapidly, with an average loss of dry weight of 94.4%, followed by Laguncularia sp. with 52.8% and Rhizophora sp. with 29.71 %, after a period of 90 days. The sediments of the area are clayey and no sand was found at the sampled depth (around 2.0 m). The salinity was around 25/00 at the surface and increased to values between 40 - 50/00 from about 50 in depth. The oxirreduction potential (eH) was positive (oxidizing) until an average depth of 50 in, becoming negative (reducing) at depth. The pH ranged from 4 to 7 in the profile, being lower from 4-5 in oxidizing eH and from 5-7 in reducing eH. Compared to work on decomposition of mangrove leaves conducted in other regions of Brazil we found decomposition rates equivalent to those we expect to determine in this work.