Stem hydraulic traits and leaf water-stress tolerance are co-ordinated with the leaf phenology of angiosperm trees in an Asian tropical dry karst forest

<p><strong>Background and Aims:</strong> The co-occurring of evergreen and deciduous angiosperm trees in Asian tropical dry forests on karst substrates suggests the existence of different water-use strategies among species. In this study it is hypothesized that the co-occurring evergreen and deciduous trees differ in stem hydraulic traits and leaf water relationships, and there will be correlated evolution in drought tolerance between leaves and stems.</p> <p><strong>Methods:</strong> A comparison was made of stem hydraulic conductivity, vulnerability curves, wood anatomy, leaf life span, leaf pressure–volume characteristics and photosynthetic capacity of six evergreen and six deciduous tree species co-occurring in a tropical dry karst forest in south-west China. The correlated evolution of leaf and stem traits was examined using both traditional and phylogenetic independent contrasts correlations.</p> <p><strong>Key Results:</strong> It was found that the deciduous trees had higher stem hydraulic efficiency, greater hydraulically weighted vessel diameter (<em>D</em>_h) and higher mass-based photosynthetic rate (<em>A</em>_m); while the evergreen species had greater xylem-cavitation resistance, lower leaf turgor-loss point water potential (π₀) and higher bulk modulus of elasticity. There were evolutionary correlations between leaf life span and stem hydraulic efficiency, <em>A</em>_m, and dry season π₀. Xylem-cavitation resistance was evolutionarily correlated with stem hydraulic efficiency, <em>D</em>_h, as well as dry season π₀. Both wood density and leaf density were closely correlated with leaf water-stress tolerance and <em>A</em>_m.</p> <p><strong>Conclusions:</strong> The results reveal the clear distinctions in stem hydraulic traits and leaf water-stress tolerance between the co-occurring evergreen and deciduous angiosperm trees in an Asian dry karst forest. A novel pattern was demonstrated linking leaf longevity with stem hydraulic efficiency and leaf water-stress tolerance. The results show the correlated evolution in drought tolerance between stems and leaves.</p>