Interação do regime hídrico com as relações nutricionais em ecossistema manguezal RESUMO (Interação do regime hídrico com as relações nutricionais em ecossistema manguezal). A hipótese de que a sazonalidade do regime fl uvial e pluvial tenha alguma infl uência na composição físico-química do sedimento e na constituição química foliar em arbóreas do ecossistema manguezal foi testada nesse estudo. ABSTRACT(Interaction of the water regime with nutrients relations in a mangrove ecosystem). Th e hypothesis that the seasonality of rainfall and the river regime have some infl uence on the physical and chemical sediment and chemical composition of tree leaves of the mangrove ecosystem was tested. In this study, the infl uence of the hydric regime on the physicochemical characteristics of the Mucuri River mangrove ecosystem, in Bahia, Brazil, was evaluated. Th e study was carried out during the months of April (rainy season) and October (dry season) in sites that were predominantly comprised of Avicennia germinans, Laguncularia racemosa and Rhizophora mangle. We evaluated the physicochemical properties of the sediments and nutrient leaf composition. Overall, the results were infl uenced by the hydric regime. Th e period of higher river levels and rainwater intake was marked by high values of exchangeable bases, cation exchange capacity, pH, salinity and Ca, Fe and Mn in the sediments. In contrast, higher values of K, Mg and Zn occurred during the dry season. Th e hydric regime also infl uenced the chemical composition of leaves. During the dry season, the concentrations of Ca, Mg, Zn, Fe and Cu were higher. Spatial variation and interspecifi c diff erences were also observed. Leaves of A. germinans showed a higher accumulation of nutrients, while lower concentration of nutrients were observed in R. mangle. Th e basin forest region (interior of forest) was characterized by high values of organic matter, pH and K. Th ese factors had little infl uence on the concentration of nutrients in the leaves. Th e lack of a clear seasonal pattern in geomorphology, geochemistry and in the chemical composition of the leaves shows the complexity of interpreting data of a coastal ecosystem where environmental factors interact synergistically and antagonistically.
. The growth, the pigments and gas exchange measurements showed no changes in response to doses of chromium. After 30 days the initiation of treatments, plants of L. racemosa had average 0.559 g of total dry weight, 1.34 mg L -1 of total chlorophyll and 7.9 μmol m -2 s -1 of A (CO 2 photosynthetic assimilation). The photochemical potential efficiency was affected by the intermediate dose of 0.05 mg L -1 of Cr +3 (Fv/Fm=0.73) and it was associated with improved translocation of chromium from root to leaves. L. racemosa accumulated Cr +3 in the root, especially in the highest dose (560 mg g -1 DW) representing twenty-eight times the value obtained in control. The concentration of chromium in stem and leaves was not influenced by the tested doses. There was a reduction of fructose and sucrose in the largest dose of chromium, suggesting the drain of these carbohydrates to meet the energy demand of root absorption. The results suggest that L. racemosa owns characteristics of a chromium-tolerant species.
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