Divergent floral hydraulic strategies in Bauhinia s.l.: lianas adopt drought tolerance while trees prioritize drought avoidance

Lianas are particularly abundant in seasonally dry tropical forests, where most species flower during the dry season. While hydraulic differences of vegetative organs between lianas and trees are well-documented, floral hydraulic strategies and their potential role in liana expansion remain unclear. To characterize divergence in floral water-use strategies between lianas and trees, we examined 24 floral traits related to water transport, storage, drought tolerance, and pollinator attraction in 16 liana and 16 tree species of Bauhinia s.l. from a tropical seasonal rainforest in Yunnan, China. Liana flowers exhibited greater petal vein density, stomatal density and size, flower mass per area, and drought tolerance than tree flowers, which showed higher saturated water content and hydraulic capacitance. Liana flowers exhibited a trade-off between hydraulic efficiency and safety, but trees did not. Life forms also differed in trait coordination linking hydraulic structure, function, and reproduction. Our findings reveal divergent floral hydraulic syndromes: lianas adopt structurally reinforced, drought-tolerant designs for canopy flowering under high vapor pressure deficit, while trees rely on internal water reserves to buffer water loss. This study provides the first organ-level evidence that divergent floral hydraulic strategies underpin reproductive success and may help explain liana dominance in seasonally dry tropical forests under climate change.