Supporting information - Gerolamo et al. 2025. Stem Xylem Differences in Congeneric Lianas Between Forests Are Unrelated to Hydraulic Safety and Efficiency. Plants

<b>Abstract</b>Lianas are known for their distinctive vascular anatomy and remarkable hydraulic efficiency. Yet they exhibit considerable variation in hydraulic safety across and within forest types. This observation suggests different structure-functional strategies among lianas growing under contrasting levels of drought. We hypothesize that the xylem anatomy of lianas vary with water availability, which determine hydraulic safety and efficiency across tropical forest types. Here, we compared xylem features from cell to intervessel pit level, testing hydraulic safety and efficiency in five pairs of congeneric Bignonieae lianas across a seasonally dry forest (SDF) and a wet rainforest (RF). The SDF liana species had a higher vessel density and grouping, and thinner fibres than rainforest lianas, but none of the features measured were related to hydraulic safety. Our results do not support that vessel or pit quantitative properties predict hydraulic safety in lianas. However, a higher hydraulic vessel diameter, total pit membrane area, and lower intervessel wall-lumen ratio was associated with high hydraulic efficiency, regardless of the forest type. These findings highlight the complexity of hydraulic structure–function relationships in lianas. While we found distinct xylem anatomical differences between species from contrasting forest types, only some traits were associated with hydraulic efficiency, and none predicted hydraulic safety, suggesting that other factors may be at play.