Water acquisition patterns of two wet tropical canopy tree species of French Guiana as inferred from H₂¹⁸O extraction profiles

Abstract

We inferred water acquisition patterns of two major tropical rainforest canopy tree species, during wet and dry seasons in different soil drainage conditions, based on the natural abundance of 18 O in soil and xylem water and on descriptions of the vertical extension of root systems. Vertical 18 O patterns in the soil were not monotonic and spatially distinct soil layers displayed similar 18 O values. Therefore, vertical patterns of water extraction could only be interpreted by combining the isotopic data with observed root and soil moisture vertical distributions. On sites with deep vertical drainage (DVD), Eperua falcata was able to absorb water down to at least -3.0 m depth, whereas Dicorynia guianensis depended solely on superficial layers. On sites with superficial lateral drainage (SLD), the rooting system of both species was less deep, but Eperua falcata was still able to extract water around -2.0 m depth. Despite these distinct patterns, there was no effect of seasonal soil drought on leaf water status. In terms of adaptation to seasonal soil drought, the strategy of Eperua falcata might be advantageous under occasional severe soil moisture stress. H 2 18 O / rainforest canopy tree / water acquisition / Eperua falcata / Dicorynia guianensis / water-use efficiency Rsum -Stratgies d'acquisition de l'eau de deux espces majeures de la fort tropicale humide guyanaise estimes par les profils d'extraction de H 2 18