Influence of the flood pulse on leaf phenology and photosynthetic activity of trees in a flooded forest in Central Amazonia/Brazil

This study was carried out over a four-year period in a blackwater flooded forest (igapo) on lower Taruma-Mirim River, Central Amazonia, in order to verify the influence of the flood pulse on the phenology and photosynthesis of two tree species, Eschweilera tenuifolia (Lecythidaceae) and Hevea spruceana (Euphorbiaceae). Phenology and photosynthesis were monitored weekly. Photosynthetic activity was measured on sun leaves, through infra-red gas analysis (IRGA). Both species are semi-deciduous and their distribution occurred mostly on the lower levels of the floodplains that remained flooded for longer and eventually uninterrupted periods. Monthly maximum mean assimilation rates of CO2 (A(max)) are related to photosynthetic activity and leaf age, mature leaves of H. spruceana showed maximum A(max) of 9.5 mumol m(-2) s(-1), whereas for E. tenuifolia the value was 8.8 mumol m(-2) s(-1). The seasonality of leaf fall seems to be a response to environmental change related to the period of high irradiance level