RESPONSE OF TWO TROPICAL TREE SPECIES, <em>PONGAMIA</em> <em>PINNATA</em> AND <em>EUGENIA</em> <em>GRANDIS</em>, TO O₃ EXPOSURES

Abstract

This paper reports a comparative study on the effects of O₃ exposure on stomatal conductance (g_s), photosynthetic rate (A) and intercellular CO₂ concentration (C_i) of two tropical tree species, Pongamia pinnata and Eugenia grandis. These seedlings were exposed to 0.1, 0.2 and 0.5 µmol mol^-1 O₃.
O₃ reduced both g_s and A after 24 h of fumigation in the two species. g_s decreased rapidly with increase in O₃ concentrations. The decline in A caused by lower concentration of O₃ is assumed to have resulted from stomatal closure. The reduction in C indicates that only a slight or no inhibition of photosynthetic CO₂ fixation was induced by O₃. Foliar symptoms were noticed when these seedlings were fumigated with higher concentrations of O₃, 0.2 and 0.5 µmol mol^-1. Judging from the degree of the appearance of visible symptoms, of the two species, E. grandis was a better O₃ avoider.