The impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana

Damien Bonal (1) , Alexandre Bosc (2) , Stéphane Ponton (1) , Jean-Yves Goret (3) , Benoît Burban (3) , Patrick Gross (1) , Jean-Marc Bonnefond (2) , Jan Elbers (4) , Bernard Longdoz (1) , Jean-Marc Guehl (5) , André Granier (1)

1 EEF - Ecologie et Ecophysiologie Forestières [devient SILVA en 2018]
2 EPHYSE - Écologie fonctionnelle et physique de l'environnement
3 ECOFOG - Ecologie des forêts de Guyane
4 Earth System Sciences - Climate change and adaptive land and water management
5 DEPT EFPA - Département Ecologie des Forêts, Prairies et milieux Aquatiques

The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5° 16'54" N; 52°54'44" W). We compared seasonal variations between wet and d1y periods and between d1y pe1iods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 gC.m-2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild d1y period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 gC m-2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe d1y pe1iod was characterised by greater carbon storage (64.6 gC.m-2), emphasizing that environmental conditions such as during a severe drought modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance.

Domaines: Sciences agricoles

Damien Bonal, Alexandre Bosc, Stéphane Ponton, Jean-Yves Goret, Benoît Burban, et al.. The impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana. Xes Journées d'Ecologie fonctionnelle, Centre National de la Recherche Scientifique, Apr 2008, La Grande Motte, France. ⟨hal-01032384⟩