The surface-atmosphere exchange of carbon dioxide in tropical rainforests: Sensitivity to environmental drivers and flux measurement methodology
- Fu, Zheng [ Montana State University: Land Resources & Environmental Sciences ]
- Gerken, Tobias [ Montana State University: Land Resources & Environmental Sciences ]
- Bromley, Gabriel [ Montana State University: Land Resources & Environmental Sciences ]
- Araújo, Alessandro [ Embrapa Amazônia Oriental, Belém, PA, Brazil ]
- Bonal, Damien [ Université de Lorraine, AgroParisTech, INRA, UMR Silva, France ]
- Burban, Benoit [ INRA, UMR Ecofog, French Guiana ]
- Ficklin, Darren [ Department of Geography, Indiana University, Bloomington, Indiana ]
- Fuentes, Jose D. [ Department of Meteorology and Atmospheric Science, The Pennsylvania State University, PA ]
- Goulden, Michael [ Department of Earth System Science, University of California, Irvine, CA ]
- Hirano, Takashi [ Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan ]
- Kosugi, Yoshiko [ Laboratory of Forest Hydrology, Graduate School of Agriculture, Kyoto University, Japan ]
- Liddell, Michael [ Centre for Tropical, Environmental, and Sustainability Sciences, College of Science and Engineering, James Cook University, Cairns, Queensland ]
- Nicolini, Giacomo [ University of Tuscia, DIBAF Department, Via San Camillo de Lellis, Italy ]
- Niu, Shuli [ Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China ]
- Roupsard, Olivier [ CATIE, Centro Agronómico Tropical de Investigación y Enseñanza, Turrialba, Costa Rica ]
- Stefani, Paolo [ University of Tuscia, DIBAF Department, Via San Camillo de Lellis, Viterbo, Italy ]
- Mi, Chunrong [ Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, University of Chinese Academy of Sciences, Beijing, China ]
- Tofte, Zaddy [ Montana State University: Land Resources & Environmental Sciences ]
- Xiao, Jingfeng [ Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, USA ]
- Valentini, Riccardo [ University of Tuscia, DIBAF Department, Via San Camillo de Lellis, Viterbo, Italy ]
- Wolf, Sebastian [ Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland ]
- Stoy, Paul C. [ Montana State University: Land Resources & Environmental Sciences ]
Tropical rainforests play a central role in the Earth system by regulating climate, maintaining biodiversity, and sequestering carbon. They are under threat by direct anthropogenic impacts like deforestation and the indirect anthropogenic impacts of climate change. A synthesis of the factors that determine the net ecosystem exchange of carbon dioxide (NEE) at the site scale across different forests in the tropical rainforest biome has not been undertaken to date. Here, we study NEE and its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), across thirteen natural and managed forests within the tropical rainforest biome with 63 total site-years of eddy covariance data. Our results reveal that the five ecosystems with the largest annual gross carbon uptake by photosynthesis (i.e. GEP > 3000 g C m(-2) y(-1)) have the lowest net carbon uptake - or even carbon losses versus other study ecosystems because RE is of a similar magnitude. Sites that provided sub canopy CO2 storage observations had higher average magnitudes of GEP and RE and lower average magnitudes of NEE, highlighting the importance of measurement methodology for understanding carbon dynamics in ecosystems with characteristically tall and dense vegetation. A path analysis revealed that vapor pressure deficit (VPD) played a greater role than soil moisture or air temperature in constraining GEP under light saturated conditions across most study sites, but to differing degrees from -0.31 to -0.87 mu mol CO2 m(-2) s(-1) hPa(-1). Climate projections from 13 general circulation models (CMIP5) under the representative concentration pathway that generates 8.5 W m(-2) of radiative forcing suggest that many current tropical rainforest sites on the lower end of the current temperature range are likely to reach a climate space similar to present-day warmer sites by the year 2050, warmer sites will reach a climate not currently experienced, and all forests are likely to experience higher VPD. Results demonstrate the need to quantify if and how mature tropical trees acclimate to heat and water stress, and to further develop flux-partitioning and gap-filling algorithms for defensible estimates of carbon exchange in tropical rainforests.