Plants react to changes in light and hydrological conditions in terms of quantity and composition of chloroplastidic pigments, which affects the photosynthetic properties and consequently the accumulation of plant biomass. Thus, the chloroplastidic pigment concentration and chlorophyll a fluorescence of three Amazonian species (Bertholletia excelsa, Carapa guianensis e Dipteryx odorata) were investigated in sun and shade leaves form the tree crown collected during two distinct periods of precipitation (dry and rainy seasons). Pigment contents were determined by spectrophotometry and fluorescence variables were determined using a portable fluorometer. The results demonstrated that the species showed high concentrations of Chl a, Chl b e Chl total during the wet season in relation to the dry season, especially in shade leaves. A higher concentration of carotenoids was found in B. excelsa, when compared with leaves of C. guianensis and D. odorata. In leaves of B. excelsa and D. odorata no significant difference was found in relation to the photochemistry of photosystem II (Fv/Fm) between the wet and dry seasons. In conclusion, the three species react differently to variations in the light and precipitation conditions regarding light capture, aspects that might be considered in the management of forest plantations.

The significance of phenological characteristics, stomatal conductance of the leaves, and stem water storage fluctuations for the regulation of xylem sap flow in an evergreen (Carapa guianensis Aubl.), in a semideciduous (Swietenia macrophylla King), and in a deciduous (Cedrela odorata L.) Meliaceae species was studied in a 7-year-old plantation near Manaus, Brazil. The study responds to the increasing demand for knowledge on the water relations of highly exploited timber trees of the Amazon. Xylem sap flow measurements indicated that the daily sap flow of Carapa (3.8 l day -1 tree -1 to 16.4 l day -1 tree -1 ) exceeded the daily sap flow of Swietenia (2.4 l day -1 tree -1 to 7.0 l day -1 tree -1 ) and Cedrela (1.6 l day -1 tree -1 to 11.6 l day -1 tree -1 ) during the entire year, although the highest flux densities were measured in Cedrela. The decrease in xylem sap flow observed in periods with low soil water potentials and high atmospheric vapor saturation deficits was more pronounced in the deciduous (Cedrela) and semi-deciduous species (Swietenia) than the evergreen species (Carapa). Carapa, which has the highest daily sap flow, had the highest biomass and sapwood portion. The high flux densities measured in Cedrela most likely result from the large earlywood vessels in this species. The seasonal variation of xylem sap flow of the three species was correlated with the stomatal conductance of the leaves measured by infiltration experiments. Stem water storage fluctuations in Carapa and Swietenia were predominantly due to transpiration; in Cedrela it was predominantly due to evaporative water loss on the stem surface during dry periods.

O feijão-caupi (Vigna unguiculata) é uma das principais culturas alimentares nas regiões Norte e Nordeste do Brasil, que concentram a maior área cultivada e produção desta leguminosa. A produtividade, nestas regiões, é de cerca de 300 kg ha -1 (Medeiros et al. 2008), não muito diferente daquela obtida no continente africano, maior região produtora, onde se registra produtividade média de 380 kg ha -1 (Ishaya et al. 2008). Segundo Silva et al. (2000) e Ishaya et al. (2008), dentre os fatores que interferem, negativamente, na cultura, o manejo inadequado das plantas daninhas que ocorrem nas áreas de cultivo contribui para a redução de produtividade. Além ABSTRACT RESUMO disso, algumas espécies de plantas daninhas servem como hospedeiros alternativos de doenças que atacam o feijão-caupi, como ocorre com a guanxuma (Sida rhombifolia), malva-sedosa (Waltheria indica), mussambê (Cleome affinis) e mela-bode (Herissantia crispa) (Assunção et al. 2006).Nesse contexto, o uso de herbicidas, como um dos componentes de programas de manejo integrado de plantas daninhas, na cultura do feijão-caupi, permite elevada eficácia de controle, com redução de custos de produção. Entretanto, dois aspectos devem ser considerados, no que se refere ao emprego de herbicidas, nessa cultura: a inexistência de herbicidas registrados no Brasil, para controle de plantas daninhas, o que impede recomenda-