BIOGEOCHEMISTRY OF MANGROVE SOIL ORGANIC-MATTER - A COMPARISON BETWEEN RHIZOPHORA AND AVICENNIA SOILS IN SOUTH-EASTERN BRAZIL

Soil core samples from Rhizophora mangle L. and Avicennia schaueriana Stapf and Leech forests from south-eastern Brazil were analysed for th eir total organic matter content and their sugars, amino acid and amin o sugars composition. Organic carbon and nitrogen contents were higher in Avicennia than in Rhizophora soils. The contribution of sugars and amino acids to the total organic carbon pool was constant with depth in Rhizophora soils whereas in Avicennia soils it increased. Spectral distribution of sugars and amino acids showed a dominance of Ca-affine monomers, particularly acidic amino acids, and the sugar arabinose. B iogeochemical indicators derived from ratios of individual sugar and a mino acid monomers confirm previous studies which showed that organic matter in both soils is mainly of mangrove origin. The results further suggest accumulation of organic matter in Rhizophora soils and a cont inuing degradation of organic matter in Avicennia soils. The latter ma y thus release more nutrients to adjacent ecosystems than Rhizophora s oils.