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Interannual and Seasonal Variations in Ecosystem Transpiration and Water Use Efficiency in a Tropical Rainforest

1
UMR EcoFoG, INRA, CNRS, Cirad, AgroParisTech, Université des Antilles, Université de Guyane, 97310 Kourou, French Guiana, France
2
Cirad, UR Forests & Societies, Université de Montpellier, 34000 Montpellier, France
3
Institut National Polytechnique Félix Houphouet-Boigny (INP-HB), Yamoussoukro, Ivory Coast
4
Laboratoire Ecologie, évolution, interactions des systèmes amazoniens (LEEISA), CNRS, IFREMER, Université de Guyane, 97300 Cayenne, French Guiana, France
5
INPE, Av. dos Astronautas, SP 12227-010 São José dos Campos, Brazil
6
Université de Lorraine, AgroParisTech, INRA, UMR Silva, 54000 Nancy, France
7
Field Science Center for Northern Biosphere, Hokkaido University, Sapporo 060-0808, Japan
*
Author to whom correspondence should be addressed.
Forests 2019, 10(1), 14; https://doi.org/10.3390/f10010014
Received: 10 November 2018 / Revised: 19 December 2018 / Accepted: 24 December 2018 / Published: 26 December 2018
(This article belongs to the Special Issue Water Cycling and Drought Responses of Forest Ecosystems)
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Abstract

Warmer and drier climates over Amazonia have been predicted for the next century with expected changes in regional water and carbon cycles. We examined the impact of interannual and seasonal variations in climate conditions on ecosystem-level evapotranspiration (ET) and water use efficiency (WUE) to determine key climatic drivers and anticipate the response of these ecosystems to climate change. We used daily climate and eddyflux data recorded at the Guyaflux site in French Guiana from 2004 to 2014. ET and WUE exhibited weak interannual variability. The main climatic driver of ET and WUE was global radiation (Rg), but relative extractable water (REW) and soil temperature (Ts) did also contribute. At the seasonal scale, ET and WUE showed a modal pattern driven by Rg, with maximum values for ET in July and August and for WUE at the beginning of the year. By removing radiation effects during water depleted periods, we showed that soil water stress strongly reduced ET. In contrast, drought conditions enhanced radiation-normalized WUE in almost all the years, suggesting that the lack of soil water had a more severe effect on ecosystem evapotranspiration than on photosynthesis. Our results are of major concern for tropical ecosystem modeling because they suggest that under future climate conditions, tropical forest ecosystems will be able to simultaneously adjust CO2 and H2O fluxes. Yet, for tropical forests under future conditions, the direction of change in WUE at the ecosystem scale is hard to predict, since the impact of radiation on WUE is counterbalanced by adjustments to soil water limitations. Developing mechanistic models that fully integrate the processes associated with CO2 and H2O flux control should help researchers understand and simulate future functional adjustments in these ecosystems. View Full-Text
Keywords: tropical rainforest; evapotranspiration; water use efficiency; drought; radiation tropical rainforest; evapotranspiration; water use efficiency; drought; radiation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Aguilos, M.; Stahl, C.; Burban, B.; Hérault, B.; Courtois, E.; Coste, S.; Wagner, F.; Ziegler, C.; Takagi, K.; Bonal, D. Interannual and Seasonal Variations in Ecosystem Transpiration and Water Use Efficiency in a Tropical Rainforest. Forests 2019, 10, 14.

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