Open AccessTemporal patterns of net CO 2 exchange for a tropical semideciduous forest of the southern Amazon Basin
Author(s) -
Vourlitis George L.,
de Almeida Lobo Francisco,
Zeilhofer Peter,
de Souza Nogueira José
Publication year - 2011
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jg001524
Subject(s) - eddy covariance , vapour pressure deficit , environmental science , primary production , photosynthetically active radiation , ecosystem , atmospheric sciences , ecosystem respiration , leaf area index , precipitation , terrestrial ecosystem , ecology , geography , photosynthesis , physics , biology , transpiration , botany , meteorology
The carbon cycling of tropical ecosystems has received considerable attention over the last 1–2 decades; however, interactions between climate variation and tropical forest net ecosystem CO 2 exchange (NEE) are still uncertain. To reduce this uncertainty, and assess the biophysical controls on NEE, we used the eddy covariance method over a 3 year period (2005–2008) to measure the CO 2 flux and energy balance for a 25–28 m tall, mature tropical semideciduous forest located near Sinop Mato Grosso, Brazil. The study period encompassed warm‐dry, cool‐wet, and cool‐dry climate conditions, and based on previous research, we hypothesized that the net CO 2 accumulation of the semideciduous forest would be lower during periods of drought. Using time series of the enhanced vegetation index (EVI), a NEE‐light‐use model, and path analysis, we found that the estimated quantum yield ( a ′, μ mol CO 2 μ mol photons −1 ) was directly affected by temporal variations in the EVI, precipitation, and photosynthetically active radiation (PAR), while the optimal rate of gross primary production ( F GPP,opt , μ mol m −2 s −1 ) was directly affected by the EVI and PAR. However, indirect effects of precipitation on the a ′ and F GPP,opt were stronger than direct effects because variations in precipitation also lead to variations in the EVI and the atmospheric vapor pressure deficit (VPD). Daytime ecosystem respiration ( F RE,day , μ mol m −2 s −1 ) was directly affected by temporal variations in temperature and VPD and indirect effects of other variables were of lesser importance. Net ecosystem CO 2 uptake was often higher in the dry season than the wet season, not because of a dry season “green‐up” but because rates of ecosystem respiration declined relatively more than rates of canopy photosynthesis. Over interannual timescales, average daily NEE increased over the 3 year study period and was highest in 2007–2008, which was also the driest year in terms of rainfall. However, 2007–2008 was also the coolest year during the 3 year study period, and the low temperature appeared to compensate for the low rainfall. Overall, our data suggest that the NEE of tropical semideciduous forests is sensitive to temporal variations in surface water availability but that indirect effects of other variables, such as temperature and VPD, are important in controlling CO 2 gain and loss. Such interactions will be important for the future NEE under warmer and drier conditions that are anticipated with anthropogenic climate change.