Effect of asymmetric stomatal response on gas-exchange dynamics

The dynamic light environment and plant responses to it have been revealed by many studies in the last two decades. Asymmetric responses in stomatal conductance (gs) are commonly observed, and a relation with water use and carbon gain of plant has been suggested. This study focused on the temporal response of gs to fluctuating light intensity and its effect on gas exchange of a leaf. The temporal gs response of a leaf was approximated by a delay system that was characterized by a time constant (τ). The response is asymmetric if the time constant τ+ for increases in gs differs from the time constant τ− for decreases in gs, and the degree of asymmetry is measured by a parameter pτ=τ−/τ+. The mean output was derived under alternating input in the delay system. The range of pτ that strongly affected the mean output was determined. A strong dependency of mean output (gs) on pτ was observed at relatively large mean input (PFD) and pτ<1 (rapid decrease in gs) or at small mean input and pτ>1 (rapid increase in gs). To confirm the effect of asymmetric gs response on gas exchange, dynamic gs and photosynthetic submodels previously proposed by other researchers were combined with an original submodel of leaf heat balance. The mean transpiration and photosynthetic rates (Ē and Ā) were calculated. The results showed that pτ in the gs submodel affected Ē more strongly than did Ā. This suggests that the asymmetry in the gs response controls the water use rather than the carbon gain under the conduction of fluctuating PFD.