Báo cáo lâm nghiệp: Gas exchange and water relations of evergreen and deciduous tropical savanna trees

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...
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Báo cáo lâm nghiệp: "Gas exchange and water relations of evergreen and deciduous tropical savanna trees"Gas exchange and water relations of evergreenand deciduous tropical savanna treesG. Goldstein F. Rada P. Rundel’ A. Azocar 2 12 2 A. Orozco1 Laboratory of Biomedical and Environmental Sciences, University of California Los Angeles, 900Veteran Ave., Los Angeles, CA 90024, U.S.A., and2 Departamento de Biologia, Facultad de Ciencias, Universidad de Los Andes, Merida, Venezuela ther evaluate water use efficiency. OurIntroduction main hypotheses are that: 1) the vascular system of the evergreen trees is more effi-Many neotropical savannas with pro- cient than the vascular system of the deci-nounced wet/dry seasonality and well- duous species for water transport; 2) thedrained soils are characterized by the structural basis for the high efficiency inpresence of both evergreen and decidu- water transport of the evergreen speciesous trees. The evergreen species grow as is more related to the cross-sectional areaisolated individuals in the oligotrophic soils of the conducting tissue per surface areawhich predominate, while the deciduous of supplied leaves (Huber values) than tospecies form small forest ’islands’ located intrinsic properties of the vascular system,on patches of richer soil (Sarmiento, such as large vessels; 3) despite the fact1984). The trees in these forest islands that the leaves of the evergreen plants are mostly drought deciduous, droppingare more scleromorphic and longer lived, itstheir leaves at the onset of the dry season. C0 assimilation rates are as high or even 2In contrast to the more pliant foliage of the higher, than the photosynthetic rates ofdeciduous species, evergreen trees tend deciduous trees; and 4) water and nitro-to have scleromorphic leaves. An ad- gen use efficie!ncies are similar betweenditional structural difference is that ever- the 2 groups of species. Some of thesegreen species have relatively large root hypotheses contradict current notionssystems allowing them access to soil concerning leai life span and physiologicalwater throughout the rainless period behavior of the plant species.(Medina, 1982; Sarmiento et al., 1985). The purpose of this study was to investi-gate gas exchange characteristics, water Materials and Methodsrelations and vascular hydraulic propertiesof 2 evergreen and 2 drought deciduous Two evergreen and 2 deciduous woody speciestree species. In addition, carbon isotope studied in the Venezuelan Ilanos (200 m wereratios of leaf tissue were measured to fur- elev., 9°37’N and 70°12’W). Curatella america- dif- and the 2 evergreen Byrsonima crassifolia, significantly water potentials were notnaspecies, initiate leaf renewal during the middle ferent between the 2 groups of speciesof the dry season, when the old leaves start to higher efficiency of water suggesting asenesce. The average leaf life span is approxi- transport in the evergreen species.mately 14 mo. Leaf longevity of the 2 droughtdeciduous species, Genipa caruto and Cochlo- Physiological estimates of hydraulicspermum vitifolium is shorter. Leaf production properties in terminal stem sections ofstarts with the onset of the rainy season, and several branches support the hypothesisleaves last for about 8-9 mo, at which time that resistances to water flow in the liquidwater is no longer available in the upper part ofthe soil profile. ...