The effects of intervessel pit characteristics on xylem hydraulic efficiency and photosynthesis in hemiepiphytic and non-hemiepiphytic Ficus species.

ABSTRACT

Xylem vulnerability to cavitation and hydraulic efficiency are directly linked to fine-scale bordered pit features in water-conducting cells of vascular plants. However, it is unclear how pit characteristics influence water transport and carbon economy in tropical species. The primary aim of this study was to evaluate functional implications of changes in pit characteristics for water relations and photosynthetic traits in tropical Ficus species with different growth forms (i.e. hemiepiphytic and non-hemiepiphytic) grown under common conditions. Intervessel pit characteristics were measured using scanning electron microscopy in five hemiepiphytic and five non-hemiepiphytic Ficus species to determine whether these traits were related to hydraulics, leaf photosynthesis, stomatal conductance and wood density. Ficus species varied greatly in intervessel pit structure, hydraulic conductivity and leaf physiology, and clear differences were observed between the two growth forms. The area and diameter of pit aperture were negatively correlated with sapwood-specific hydraulic conductivity, mass-based net assimilation rate, stomatal conductance (gs ), intercellular CO2 concentration (Ci ) and the petiole vessel lumen diameters (Dv ), but positively correlated with wood density. Pit morphology was only negatively correlated with sapwood- and leaf-specific hydraulic conductivity and Dv . Pit density was positively correlated with gs , Ci and Dv , but negatively with intrinsic leaf water-use efficiency. Pit and pit aperture shape were not significantly correlated with any of the physiological traits. These findings indicate a significant role of pit characteristics in xylem water transport, carbon assimilation and ecophysiological adaptation of Ficus species in tropical rain forests.