The boundary layer and the apparent responses of stomatal conductance to wind speed and to the mole fractions of CO2and water vapour in the air

摘要

ABSTRACTThe experiments and simulations reported in this paper show that, for stomata sensitive to both CO2and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response ofgwsto ambient air CO2mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses ofgwsfor χcaand χwaeach include responses to both χciandDws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χciandDws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response ofgwsfor a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses ofgwsto χciandDws, the apparent responses ofgwstoDwaand χcadepend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with diffe