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Diversité des mécanismes de résistance à la sécheresse des arbres en forêt tropicale humide

Abstract : Tropical rainforests play a central role in biogeochemical cycles at the global scale. Seasonal droughts alter their functioning, but severe droughts can severely affect tree growth and mortality. Increasingly frequent severe droughts in the past decades over the entire Amazon Basin have triggered changes in tree community composition, but our capacity to predict the fate of these communities is partly hampered by our lack of knowledge on the physiological mechanisms involved in tree drought-resistance. This thesis explores the interspecific diversity of drought resistance mechanisms of tropical rainforest tree species in French Guiana and aims at enhancing our present knowledge on their functioning. This thesis reveals that tropical rainforest canopy tree species can be very resistant to drought-induced stem embolism and that a majority of species achieve high hydraulic safety during the dry season, with strong interspecific differences. However, for most trees, a decrease in soil water availability leads to a decrease in their sap flux density during the dry season, with part of their sensitivity being related to physiological mechanisms involved in drought-resistance strategies. The underlying physiological mechanisms to their strategies vary strongly between species for young tree saplings. Some benefit from an early stomatal closure and low minimum leaf conductance, while others are more resistant to stem embolism and rely on a positive hydraulic vulnerability segmentation. During a severe imposed drought, there was a strong reduction in carbohydrate contents, which highlights the interdependence between the water and carbon balance of trees. However, the main physiological mechanism causing tree mortality seems to be hydraulic failure. The strong interspecific variability within these communities could lead to contrasting responses of tree populations to an increase in the frequency and severity of drought events, which could impact tree community composition in French Guiana.
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Submitted on : Thursday, September 9, 2021 - 10:04:04 AM
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  • HAL Id : tel-03338863, version 1

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Camille Ziegler. Diversité des mécanismes de résistance à la sécheresse des arbres en forêt tropicale humide. Biologie végétale. Université de Lorraine, 2021. Français. ⟨NNT : 2021LORR0061⟩. ⟨tel-03338863⟩

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