Abstract: Widespread drought‐induced tree mortality emphasizes the need to clarify how plants coordinate water transport through stomatal regulation and hydraulic vulnerability segmentation, two key Here, we explore their functional linkage and compare their predictive ability of mortality under an extreme drought. We quantified 11 hydraulic and stomatal traits of 20 woody species from a dry-hot savanna in Southwest China, where plants experience intense water stress. We found a decoupling between stomatal gas exchange and leaf and stem hydraulic efficiency. Leaf turgor loss point (Ψ_tlp, -2.20 ± 0.55 MPa) was more significantly more negative than leaf embolism resistance (P_50leaf, -1.75 ± 0.74 MPa), resulting in negative stomatal safety margins (SSM_tlp, Ψ_tlp-P_50leaf, -0.38 ± 0.56 MPa). But P_50leaf was significantly less negative than that of stems (P_50stem, -4.86 ± 1.99 MPa), resulting in positive leaf-stem vulnerability segmentations (P_50leaf-stem, 2.87 ± 1.81 MPa). Notably, there was a significant tradeoff between SSM_tlp and P_50leaf-stem(P< 0.05), indicating savanna species with risky stomatal regulation have larger leaf-stem vulnerability segmentation to protect stem hydraulic integrity while sustaining carbon gain. Moreover, SSMtlp was the only hydraulic trait significantly related to branch dieback ratio (P < 0.05), highlighting risky stomatal regulation as a key determinant of branch dieback in savanna species. Our study extends the vulnerability segmentation hypothesis by incorporating stomatal regulation into the classic leaf-stem vulnerability segmentation framework and enhances the prediction of drought-induced mortality in savanna ecosystems.

Key words: drought, hydraulic failure, hydraulic vulnerability segmentation, stomatal regulation, drought-induced tree mortality, stomatal safety margin, xylem embolism resistance