Photosynthetic and stomatal responses of two tropical and two temperate trees to atmospheric humidity

Abstract

The effects of leaf to air vapour pressure differences (ΔW) on net photosynthetic rate (P(N)) and stomatal conductance (g(s)) were examined in the leaves of two tropical rain forest trees, Eugenia grandis and Pongamia pinnata, and two temperate evergreen trees, Viburnum awabuki and Daphniphyllum macropodum. A single leaf was set inside a small chamber and ΔW was varied from 7 to 24 mmol mol-1 at 25 and 500 μmol m-2 s-1 of photon flux density. P(N) and g(s) of the two tropical rain forest trees decreased with increasing ΔW, while the two temperate evergreen trees were not highly responsive to ΔW. P. pinnata was more sensitive to ΔW in its stomatal response, and had a higher stomatal density and higher stomatal index than did the two temperate trees and another tropical tree. Significant reductions in g(s) and intercellular CO2 concentrations in the two tropical trees at high ΔW suggest that the decline of P(N) was due to the decrease in g(s). The responses of P(N) and g(s) indicated that the tropical trees were more sensitive to ΔW than were the temperate ones.