A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Light Response Curves of three plants in different strata in an ecoton tropical forest –SavannaEduardo Jacusiel Miranda 1 (aquaviva@terra.com.br), Clóvis Lasta Fritzen, José HolandaCampelo Jr. 1 ,José de Souza Nogueira 1 , Nicolau Priante Filho 1Universidade Federal de Mato Grosso - Depto. de Física - Grupo de Física e MeioAmbiente - Av. Fernando Correa da Costa s/n, 78060-900 -Cuiabá -MT Brasil.George Louis Vourlitis (georgev@csusm.edu) Biological Sciences Program- CaliforniaState University- San Marcos, CA 92096-0001, USAMeasurements of CO 2 and water vapor flux using eddy covariance are being made from a40m tower located in a transitional tropical forest near Sinop Mato Grosso. Ascomplementary information to this study, the photosynthetic light response curves ofthree trees located near the tower were measured at different heights in the forest canopywith the objective of understanding seasonal and spatial (height in the forest canopy)trends in the photosynthetic light response. The measurements were in a canopy emergenttree (30 m tall) identified as Catanudo and in two other sub-canopy (14 m tall) treeslocally identified as Canela and Laranjeira (positive identification of all species is currentunder investigation). Measurements were made in the wet season (January), transitionwet-dry (April), dry season (June and August), and in the dry-wet transition (September)of 2001. For Catanudo, measurements were made at two different heights of 26m (at thetop of the canopy) and 18m, while measurements on the other trees were made at 10mabove ground. In the wet season the Catanudo exhibited a photosynthesis rate at lightsaturation (P max ) of 9.4 µmol m -2 s -1 while Laranjeira and Canela had a P max of 10.0 and5.5 µmol m -2 s -1 , respectively. In the dry season (June) the values of P max were of 7.1,11.0 and 7.4 µmol m -2 s -1 respectively for the Catanudo, Laranjeira and Canela, so whileCatanudo experienced a decline in P max from the wet to the dry season, Canela andLaranjeira had increases in P max . The leaves of Catanudo at different heights (26 and18m) presented different physiological behavior. The leaves at 26m had larger rates ofP max compared to sub-canopy leaves regardless of season, however, sub-canopy leavesshowed much less seasonal variability in the photosynthetic light response than canopyleaves. These data suggest that species responses to seasonal variations in rainfall arevariable. In addition, although leaves at the top of the canopy have larger rates of P max ,the small seasonal variation in sub-canopy leaves may be important for CO 2 uptakeduring the dry season.