STOMATAL RESPONSES TO A RANGE OF VARIABLES IN 2 TROPICAL TREE SPECIESGROWN WITH CO2, ENRICHMENT

Seedlings of Maranthes corymbosa (Blume) and Eucalyptus tetrodonta (F. Muell) were grown with or without CO2 enrichment (700 mu mol CO2 mol( -1)). The response of stomatal conductance (g(s)) to leaf drying, exog enous abscisic acid and calcium ions was investigated in M. corymbosa. Reciprocal transfer experiments were also conducted whereby plants we re grown in one treatment and then transferred to the other before g(s ) was measured. Stomatal conductance in M. corymbosa was more sensitiv e (a greater percentage decline in g(s) per unit percentage decline in leaf fresh weight) to leaf water status under conditions of CO2 enric hment compared to ambient conditions. However, the rate of reduction o f g(s) in response to exogenous abscisic acid was not influenced by CO 2 treatment. In contrast, the rate of reduction of g(s) in response to exogenous CaCl2 was decreased under conditions of CO2 enrichment. Rec iprocal transfer experiments showed that exposure to CO2 enrichment re sults in a short-term, reversible decline in g(s) as a result of decre ased stomatal aperture and a long-term, irreversible decline in g(s) a s a result of a decreased stomatal density. Seedlings of E. tetrodonta were used to investigate the response of g(s) to light flux density, leaf-to-air vapour pressure difference (LAVPD), leaf internal CO2 conc entration (C-i) and temperature. Reciprocal transfer experiments were also conducted. CO2 enrichment did not influence the pattern or sensit ivity of response of g(s) to LAVPD and C-i in E. tetrodonta. In contra st, the slope of the response of g(s) to temperature decreased for tre es grown under elevated [CO2](a) conditions and the equilibrium g(s) a ttained at saturating light was also decreased for plants grown under elevated [CO2](a) conditions.