Seasonal variations in C and water cycling of a tropical transitional forest.
Vourlitis, George*,1, Priante-Filho, Nicolau2, de Souza Nogueira, Jose2, de Almeida Lobo, Francisco2, Raiter, Fernando3, Valentini, Carla2, 1 Department of Biological Sciences, San Marcos, CA, USA2 Departamento de Fisica, Cuiaba, Mato Grosso, Brazil3 Instituto Universitario do Norte Matogrossense, Sinop, Mato Grosso, Brazil
ABSTRACT- Measurements of net ecosystem CO2 exchange and evapotranspiration of a tropical transitional (ecotonal) forest near Sinop-MT were made between August 1999-present using eddy covariance measurement techniques. Measurements of leaf photosynthesis, plant water potential, soil respiration, and litter fall were also made to determine how component C and/or H2O fluxes contributed to the temporal patterns in forest CO2 and H2O exchange. Data indicate that leaf and forest gas exchange is strongly affected by seasonal variations in rainfall. For example, leaf gas exchange and water potential and soil respiration are on average 2-fold lower while litter fall is 4-5 times higher during the dry season (June-August). While variations in maximum gross primary production, canopy conductance and ecosystem respiration also followed trends in rainfall, variations in these whole-forest indices of gas exchange tended to lag behind rainfall by 1-2 months. These data suggest that seasonal variations in rainfall affect canopy CO2 and H2O exchange processes in a complex manner. Furthermore, comparisons between the transitional forest and less seasonal rain forests suggest that the magnitude in the seasonal variation in CO2 exchange is somewhat unique to the transitional forest. These data suggest that potential warming and drying of tropical forest may cause seasonal variations in CO2 and H2O vapor exchange to increase in the future.
Key words: Rainforest, Amazon, Brazil
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