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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Gas exchange and water relations of evergreen and deciduous tropical savanna trees. | 448s Ann. Sci. For. 1989 46 suppl. 448s-453s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Gas exchange and water relations of evergreen and deciduous tropical savanna trees G. Goldstein1 F. Rada2 p. Rundel1 A. Azocar2 and A. Orozco2 1 Laboratory of Biomedical and Environmental Sciences University of California Los Angeles 900 Veteran Ave. Los Angeles CA 90024 U.S.A. and 2 Departamento de Biologia Facultad de Ciencias Universidad de Los Andes Merida Venezuela Introduction Many neotropical savannas with pronounced wet dry seasonality and well-drained soils are characterized by the presence of both evergreen and deciduous trees. The evergreen species grow as isolated individuals in the oligotrophic soils which predominate while the deciduous species form small forest islands located on patches of richer soil Sarmiento 1984 . The trees in these forest islands are mostly drought deciduous dropping their leaves at the onset of the dry season. In contrast to the more pliant foliage of the deciduous species evergreen trees tend to have scleromorphic leaves. An additional structural difference is that evergreen species have relatively large root systems allowing them access to soil water throughout the rainless period Medina 1982 Sarmiento etal. 1985 . The purpose of this study was to investigate gas exchange characteristics water relations and vascular hydraulic properties of 2 evergreen and 2 drought deciduous tree species. In addition carbon isotope ratios of leaf tissue were measured to fur ther evaluate water use efficiency. Our main hypotheses are that 1 the vascular system of the evergreen trees is more efficient than the vascular system of the deciduous species for water transport 2 the structural basis for the high efficiency in water transport of the evergreen species is more related to the cross-sectional area of the conducting tissue per surface area of supplied leaves Huber values than to intrinsic properties of the vascular system such as large .
