Stomatal responses to a range of variables in two tropical tree species grown with CO2 enrichment

Seedlings of Maranthes corymbosa</it> (Blume) and Eucalyptus tetrodonta</it> (F. Muell) were grown with or without CO<inf>2</inf> enrichment (700μmol CO<inf>2</inf> mol−1 The response of stomatal conductance (g<inf>2</inf>) to leaf drying, exogenous absclslc acid and calcium ions was investigated in M. corymbosa</it>. Reciprocal transfer experiments were also conducted whereby plants were grown in one treatment and then transferred to the other before g, was measured. Stomatal conductance in M. corymbosa</it> was more sensitive (a greater percentage decline in g<inf>2</inf> per unit percentage decline in leaf fresh weight) to leaf water status under conditions of CO<inf>2</inf> enrichment compared to ambient conditions. However, the rate of reduction of g<inf>2</inf> in response to exogenous abscisic acid was not influenced by CO<inf>2</inf> treatment. In contrast, the rate of reduction of g<inf>2</inf>, in response to exogenous CaCl<inf>2</inf> was decreased under conditions of CO<inf>2</inf> enrichment. Reciprocal transfer experiments showed that expo sure to CO<inf>2</inf> enrichment results in a short-term, reversible decline in g<inf>2</inf>, as a result of decreased stomatal aperture and a long-term, irreversible decline in g<inf>2</inf> as a result of a decreased stomatal density. Seedlings of E. tetrodonta</it> were used to investigate the response of g<inf>2</inf> to light flux density, leaf-to-air vapour pressure difference (LAVPD</it>), leaf internal CO<inf>2</inf> concentration (C<inf>1</inf> and temperature. Reciprocal transfer experiments were also conducted. CO<inf>2</inf> enrichment did not influence the pattern or sensitivity of response of g to LAVPD and C in E. tetrodonta. In contrast, the slope of the response of g<inf>2</inf>, to temperature decreased for trees grown under elevated [CO<inf>2</inf>]<inf>a</inf> conditions and the equilibrium g<inf>2</inf> attained at saturating light was also decreased for plants grown under elevated [CO<inf>2</inf><inf>a</inf>. conditions.