Ecofisiologia de plantas lenhosas jovens de cerrado sob irradiâncias contrastantes.
Ronquim, Carlos Cesar
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We evaluated long term responses, such as survivorship, growth, photosynthetic capacity and leaf nutrient content on potted young plants of Cybistax antisyphilitica (Mart) Mart. (Bignoniaceae), Tabebuia chrysotricha (Mart. ex DC) Mart. (Bignoniaceae), Anadenanthera falcata Benth. Speg. (Mimosoideae), Stryphnodendron adstringens Mart. Coville (Mimosoideae), and Copaifera langsdorffii Desf. (Caesalpinioideae) growing in open and in shaded area without water stress. The survivorship, biomass accumulation, height and total leaf area were linked with higher photosynthetic capacity on area basis in open area. Shaded young plants showed higher leaf nutrient content on mass basis (g kg-1), lower respiration in dark, and modified the biomass partition presenting greater mean values of leaf area rate, and smaller values of the specific leaf mass. High transitory concentrations of CO2 increased the photosynthetic capacity in both irradiance conditions. However, the largest apparent carboxylation efficiency values were reached in open area. S. adstringens was unable to stay for long period in shade. The leaf gas exchange, leaf water potential and chlorophyll fluorescence were measured during daily courses in Vochysia tucanorum (C.K. Spreng.) Mart. (Vochysiaceae) and C. langsdorffii during dry and wet seasons to point out shortterm responses of carbon and water balances. The shade condition provoked higher mortality of V. tucanorum during dry season and imposed environmental constraints for V. tucanorum and C. langsdorffii due to the lower values of leaf water potential (Ψ), net photosynthesis (A) and potential photochemical efficiency (Fv/Fm). The higher C. langsdorffii survivorship in shade seems to be related with fast and high biomass accumulation in root during early growth. The sunflecks that took place under canopies are more effective in the rainy season than dry season for carbon assimilation in C. langsdorffii, and seems to cause photoinhibition in dry period by reason of excessive irradiance intensity and lower Ψ values. A careful characterization of growth and photosynthetic performances of young plants of Cerrado species in contrasting irradiances has provided important understanding of ecological conditions behind natural regeneration in Cerrado domain. It enhances the reliability of forest management methods.