Relação da estrutura e fotossíntese em espécies de mangue no Rio São Mateus

Abstract

The salinity constitutes the main developmental and productivity tensor and regulator of mangrove forests. However this vegetation is quite morphologically and physiologically adapted to survive under these conditions. Due to importance of the mangrove ecosystem, this study aimed to evaluate photosynthetic performance and structural features of Rhizophora mangle L. and Laguncularia racemosa (L.) Gaerth growing up on both low and high salinity area, at mangrove fringes. The analyses were conducted in two mangroves on River São Mateus estuary in Conceição da Barra city: The first area (A1) of lower salinity; and the second one (A2), located near River São Mateus mouth, of higher salinity. Vegetation characterization was obtained from DAP parameters, height and stem number by individual. Chlorophyll a fluorescence, gas exchange and chloroplast pigments content measurements were obtained from five fully expanded young leaves (six young individuals by each species) chosen randomly. At lower salinity area L. racemosa was the most representative specie and Avicennia germinans (L.) Stearn and R. mangle were also present. By the other hand, at higher salinity area R. mangle was the dominant specie while L. racemosa and Avicennia schaueriana Stapf & Lechman were less representing. Chlorophyll a fluorescence parameters were changed at higher salinity area indicating there be a stress salt effect over PSII transport electron activity, mainly on R. mangle. In addition, at this same area, R. mangle showed more reduced levels of Fv/Fm, electron flux by reaction center (ET0/RC), heat dissipation by reaction center (DI0/RC) and performance index for energy conservation for PSI end acceptors reduction (PITOTAL) than L. racemosa. Chloroplast pigments content also suffered variation by the salt level, since chlorophyll a content and chlorophyll a/b ratio decreased and chlorophyll b and carotenoids contents increased at higher salinity conditions. Nevertheless, R. mangle showed more carbon assimilation rate, chlorophyll a/b ratio and water use efficiency than L. racemosa at higher salinity area. The physiological performance improved of R. mangle, in addition to better adaptation features like soil support conditions and tissue oxygenation which favors it over flood conditions present in mangrove fringes, allowed it to have predominance over mangrove fringes, even in adulthood.