Vulnerability to drought-induced xylem embolism is a key parameter for drought tolerance of
vascular plants, especially in areas that will experience an increase in drought intensity and
frequency associated with climate change. However, the anatomical and chemical determinants of embolism by gas entry are poorly understood, with marginal data relating to tropical species. Although the mechanism of “air-seeding” via openings in secondary walls of conduits (i.e., bordered pits) has been described many times, our mechanistic understanding remains simplistic and suffers from a lack of detailed observations of bordered pit membranes. An indepth structure-functional approach is also needed to better understand the occurrence of xylem embolism in leaves, which are frequently assumed to be more vulnerable to hydraulic failure than branches. Based on anatomical observations and hydraulic measurements for samples from the same tree, we aim to explain interspecific variability in xylem embolism resistance by vessel and bordered pit characteristics. Measurements will be conducted for a total of 25 species from French Guiana. We will take advantage of the expertise in electron microscopy at Ulm University for pit membrane observations. We expect that our anatomical observations such as pit membrane thickness will largely explain the variation in xylem embolism resistance, both at the leaf and branch level, for tropical rainforest trees that experience seasonal drought. An improved mechanistic understanding of drought tolerance and hydraulic failure is especially relevant given current concerns about climate change and predicted shifts in Amazon rainfall.