Abstract
Errors as small as 1 C in the measurement of leaf temperature (Tleaf) are shown to cause significant changes in the estimated value of the stomatal resistance (expressed in terms of total resistance to water vapor transfer, ∑rH2O). The effect increases as Tleaf increases and as ambient relative humidity increases, if other conditions are maintained constant. The effect on the key CO2 exchange parameter, the intracellular (or mesophyll) resistance, rint, tends to be small under open stomata conditions but increases rapidly as stomatal closure occurs, particularly if the true value of rint is relatively small.
Errors in the determination of the ambient water vapor and CO2 concentrations can also significantly affect the calculated value of ∑rH2O and rint. The effect on ∑rH2O and ∑rCO2 increases as the ratio of the inlet/outlet concentration departs from unity and also increases as the assumed leaf-air concentration difference decreases. The combined effect on rint tends to be less than the individual effects on ∑rH2O and ∑rCO2 since both are in the same direction.
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