Stem photosynthetic efficiency across woody angiosperms and gymnosperms with contrasting drought tolerance

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.