Investigation of vascular limitations on floral water loss in temperate woody species

Abstract

In temperate biomes, limitations imposed by vascular physiology may influence floral water use in woody species. Freeze-thaw induced embolism in the xylem can reduce vascular transport capacity in the early spring, potentially limiting growth. To investigate whether xylem transport capacity impacts floral physiology, I quantified inflorescence water loss rates and stem hydraulic conductivity of five woody species that flower before producing leaves. I found inflorescence size and ambient temperature at flowering positively correlated with water loss. However, I detected no correlation between branch level floral water loss and stem hydraulic conductivity within species. Furthermore, a comparison of branch level water loss rates from inflorescences and leaves showed that leaf water loss is 2–4 orders of magnitude greater than that of flowers. To evaluate whether flowers were primarily phloem or xylem hydrated, I modeled the amount of water brought in during floral development and full bloom. Despite their relatively low rates of water loss, the model indicates that flowers in this study obtain the majority of their water from the xylem. Overall, the data suggest that within species floral water loss may not be limited by the xylem during flowering, but large differences in floral water loss and stem conductivity among species could explain hydraulic trait variation between large and small flowered plants.