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

WATER POTENTIAL OF PLANTS IN DIFFERENT CONDITIONS OF LIGHTINTENSITY IN ATROPICAL RAIN FOREST – SAVANNA ECOTONE OF MATOGROSSOPedro Correto Priante 1 (Rua dos Eucaliptos, n. 7 Quadra 15, J. das Palmeiras – Cuiabá-MT –Brazil pedropri@terra.com.br), Eduardo Jacusiel Miranda 1 , Clóvis Lasta Fritzen 2 , NicolauPriante Filho 1 , José de Souza Nogueira 1 and George Louis Vourlitis 31 Universidade Federal de Mato Grosso; 2 Universidade Federal de Mato Grosso do Sul;3 California State University San MarcosMeasurements of the water potential of transitional tropical forest understorey plants weremade seasonally to determine the effect of seasonal variations in rainfall on plant-waterstatus. The study was conducted in an intact transitional forest stand located near Sinop,Mato Grosso, and we chose plants that were common to the region, Quiina pteridophyllaand Dinizia excelsa, in different conditions of luminosity (plants located in gap and shadedareas). The measurements were made in 2 young and 3 adult individuals per species duringthe wet season, transition wet-dry season, dry season, and transition dry-wet season. The Q.pteridophylla individuals presented large season variation in water potential. The Q.pteridophylla in the wet season had an average water potential of –0.5MPa, 1.7 MPa in thetransition from the wet-dry season, -2.7 MPa in the dry season and, –1.7MPa in the transitionbetween the dry-wet season. Adult trees had an average water potential of –0.9MPa in thewet season;-1.2 MPa during the wet-dry season transition, and a –3.8MPa water potential atthe end dry season. The location of plants beneath the canopy (gap vs. shaded areas) had astrong influence on the water potential of D. excelsa and Q. pteridophylla individuals. Forexample, D. excelsa plants growing in shaded areas had a water potential of -1.1 MPa in thetransition wet-dry season while D exelsa individuals growing in gaps had a water potential of–1.5MPa. Following the same tendency, Q. pteridophylla plants growing in shade had anaverage water potential of –2.1MPa while plants growing in gaps had a water potential of –3.4MPa during the dry season. These data suggest that plant water potential is stronglycontrolled by seasonal variations in rainfall and the canopy light regime. These spatial andtemporal trends have important implications for the seasonal variations in leaf and canopygas exchange.