Résumé
The hydraulic segmentation hypothesis predicts that hydraulic constriction occurs close to leaves, as “bottlenecks”, in order to preserve lower water potentials, and promote drought-induced embolism containment in easy-to-renew organs. The vulnerability segmentation hypothesis predicts that leaves should be more vulnerable to the drought-induced embolism than stems. These two mechanisms should lead leaves to act as “safety valves” to protect perennials organs. With the increasing issue relative to drought resistance and climate change, the vulnerability segmentation has been intensively investigated in past years, although there is a lack of investigations for Neotropical trees. The hydraulic segmentation is more old-fashion and less investigated. Today, no study has investigated if these two sides of segmentation are related across species. We investigated across 15 Neotropical canopy tree species xylem vulnerability to embolism in stem (Cavi1000 method) and leaves (optical method) to assess an index of vulnerability segmentation. We used theoretical leaf-specific conductivity through an anatomical approach, to assess an index of hydraulic segmentation (Tyree & Ewers 1991). Our objectives were (i) to test the existence of vulnerability and hydraulic segmentations for Neotropical trees, and (ii) to test if these two mechanisms are related or not across species