Stem photosynthesis and hydraulics are not coordinated in photosynthetic stems in a tropical xerophytic scrub

Stem photosynthesis is common in multiple seasonally dry biomes, however, most of current knowledge comes from studies done in desert and Mediterranean-type ecosystems. In the tropics, plants with photosynthetic stems also occur in tropical dry forests and xerophytic scrubs, which are among the most threatened terrestrial ecosystems. Research in warm deserts has shown that stem photosynthesis and water transport (hydraulics) are interconnected, with species having greater stem hydraulic conductance also maintaining greater stem stomatal conductance and photosynthetic rate. We tested whether this hypothesis holds true in drought-deciduous and evergreen trees and shrubs from a tropical xerophytic scrub in the Macanao Peninsula, Margarita Island, Venezuela, an area impacted by open-cast sand mining. Exploring the potential coordination between photosynthetic and hydraulic traits within and among organs will give us insights into the functional strategies plants use to cope with seasonal drought and disturbance in this site. To this aim, we measured photosynthetic rate ( A area ), transpiration rate ( E ), stomatal conductance ( g s ), and carbon and nitrogen isotope ratios (δ 13 C and δ 15 N) in leaves and photosynthetic stems, and stem hydraulic traits in 12 tree and shrub species. We found no relationship between sapwood-specific hydraulic conductivity (K S ) and stem A area . However, species with high K S also had high leaf δ 13 C, indicating that efficient stem water transport is associated with leaves having greater long-term integrated water-use efficiency. Interestingly, species with higher stem A area also exhibited higher stem water-use efficiency, both intrinsic and instantaneous. Results suggest a coordination of hydraulics and photosynthetic traits between leaves and stems but not within photosynthetic stems. Our results also suggest higher variability in economic traits in photosynthetic stems than in leaves, indicating potential differences in the selection of photosynthetic traits in leaves and stems.