Drought stress recovery of hydraulic and photochemical processes in Neotropical tree saplings

International audienc

Vulnerability and hydraulic segmentations at the stem‐leaf transition: Coordination across Neotropical trees

Hydraulic segmentation at the stem-leaf transition predicts higher hydraulic resistance in leaves than in stems. Vulnerability segmentation, however, predicts lower embolism resistance in leaves. Both mechanisms should theoretically favour runaway embolism in leaves to preserve expensive organs such as stems, and should be tested for any potential coordination. We investigated the theoretical leaf-specific conductivity based on an anatomical approach to quantify the degree of hydraulic segmentation across 21 tropical rainforest tree species. Xylem resistance to embolism in stems (flow-centrifugation technique) and leaves (optical visualisation method) was quantified to assess vulnerability segmentation. We found a pervasive hydraulic segmentation across species, but with a strong variability in the degree of segmentation. Despite a clear continuum in the degree of vulnerability segmentation, eight species showed a positive vulnerability segmentation (leaves less resistant to embolism than stems), while the remaining species studied exhibited a negative or no vulnerability segmentation. The degree of vulnerability segmentation was positively related to the degree of hydraulic segmentation, such that segmented species promote both mechanisms to hydraulically decouple leaf xylem from stem xylem. To what extent hydraulic and vulnerability segmentation determine drought resistance requires further integration of the leaf-stem transition at the whole-plant level, including both xylem and outer-xylem tissue.Recherches Avancées sur l'Arbre et les Ecosytèmes ForestiersCEnter of the study of Biodiversity in Amazoni

Hydraulic and vulnerability segmentations at the leaf-stem interface: Do they exist and are they coordinated across Neotropical trees?

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 specie

Drought tolerance traits in Neotropical trees correlate with the composition of phyllosphere fungal communities

International audiencePlant-associated microorganisms have shown to aid plants in coping with drought. However, the underlying mechanisms are poorly understood and there is uncertainty regarding which microbial taxa and functions are mostly involved. We explored these issues in Neotropical rainforests and identified foliar microorganisms that may play a role in drought tolerance of trees. Our objectives were to (1) test the relationship between drought tolerance traits in Neotropical trees and the diversity and composition of their foliar fungal and bacterial communities and (2) identify leaf microbial taxa positively or negatively associated with drought tolerance traits. Our results showed that the composition of leaf fungal communities, but not bacterial communities, was related to drought tolerance. We identified 27 fungal Amplicon Sequence Variants (ASVs) whose relative abundance co-varied with drought tolerance traits. Most variants were assigned to fungal clades often described as plant pathogens and increased in abundance with drought susceptibility. This greater relative abundance of leaf pathogens in the most drought-susceptible trees might increase their vulnerability to climate change. Moreover, we identified the Strelitziana and Ochroconis fungal genera as potential candidates for future culture-dependent studies aimed at understanding and improving drought tolerance in Neotropical forests