Acclimation of water transport property to different irradiance in evergreen Quercus glauca and Eurya japonica seedlings.

Abstract

Evergreen arboreal Quercus glauca and shrubby Eurya japonica are the common species in secondary forest in warm temperate broad-leaved forest in Japan. To clarify the effect of light condition on water transport properties in these species, we studied xylem transport property, xylem structure, leaf mass and diurnal course of gas exchange for saplings grown under contrasting light conditions: full, 10 and 3% sunlight. For Q. glauca, not large diameter but double number of vessel was found under full sunlight condition while xylem hydraulic conductivity (K_s) was not different between full sunlight and shaded condition. Total leaf area per a plant tended to be smaller and leaf specific hydraulic conductivity (LSC) tended to be larger in full sunlight than in shading. Daytime depression in stomatal conductance (g_s) was observed in Q. glauca under full sunlight, contributing the avoidance of daily drought stress. For E. japonica, vessel diameter, vessel density and K_s were restricted under full sunlight while total leaf area was smaller, leading higher LSC. Less depression in g_s was observed at daytime under full sunlight for this species. Results reveals that Q. glauca under high irradiance maintain leaf water supply without remarkable restriction of leaf biomass by both xylem structure and diurnal stomatal regulation, whereas, E. japonica adjusted to full sunlight by limiting leaf biomass rather by acclimating xylem structure to retain leaf water supply.