Direct and indirect effects of light on stomata II. InCommelina communisL.

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Abstract
Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO2assimilation rate, and intercellular CO2concentration (Ci), using whole shoots ofCommelina communisL. In the first, conductance increased with decreasing Ci, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or Ci, In the second, conductance increased hyperbolically with increasing quantum flux density while Ciwas held constant at 466, 302, and 46 μmiolmol−1, and the response differed at each Ci. In neither experiment was conductance consistently related to net CO2assimilation rate in the mesophyll. In both experiments high Cisuppressed the response of conductance to light, while there was a large response of conductance to light at low Ci, indicating an interaction between the effects of light and CO2on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO2concentrations, and not that stomata maintain a ‘constant Ci’.