Key messageStem photosynthesis seems to play an adaptive role for woody plants that prosper in hot and dry ecosystems.Stem photosynthesis is thought to be involved in tree resistance/resilience to water shortage. Recent studies have focused on the coordination between stem photosynthesis and hydraulics, but the generality of association of stem photosynthetic efficiency with species-specific adaptation to drought is still unclear. We quantified bark and wood chlorophyll a fluorescence (in terms of F-v/F-m) in current-year, 1-year and 2-year-old stems of several woody species harvested in diverse habitats. We ranked species in terms of relative drought tolerance on the basis of their vulnerability to xylem embolism (P-50), and compared stem photosynthetic efficiency of drought-tolerant vs drought-sensitive species. F-v/F-m values decreased with increasing stem age, and were generally higher for Angiosperms than Gymnosperms. F-v/F-m both at the bark and wood level was higher for drought-tolerant Angiosperms compared to drought-sensitive ones. Our results highlight the potential adaptive role of stem photosynthesis in drought-tolerant species, thriving under arid conditions likely leading to prolonged stomatal closure and halt of leaf-level carbon gain.
