Water acquisition patterns of two wet tropical canopy tree species of French Guiana as inferred from (H2O)-O-18 extraction profiles

We inferred water acquisition patterns of two major tropical rainforest can opy tree species, during wet and dry seasons in different soil drainage con ditions, based on the natural abundance of O-18 in soil and xylem water and on descriptions of the vertical extension of root systems. Vertical O-18 p atterns in the soil were not monotonic and spatially distinct soil layers d isplayed similar O-18 values. Therefore, vertical patterns of water extract ion 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 lay ers. On sites with superficial lateral drainage (SLD), the rooting system o f 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 ef fect of seasonal soil drought on leaf water status. In terms of adaptation to seasonal soil drought, the strategy of Eperua falcata might be advantage ous under occasional severe soil moisture stress.