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Articles

Effect of Errors in Measuring Leaf Temperature and Ambient Gas Concentration on Calculated Resistances to CO₂ and Water Vapor Exchanges in Plant Leaves

^a Department of Environmental Biology, Research School of Biological Sciences, Australian National University, P. O. Box 475, Canberra, A.C.T. 2601, Australia

Errors as small as 1 C in the measurement of leaf temperature (T_leaf) 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 T_leaf 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, r_int, tends to be small under open stomata conditions but increases rapidly as stomatal closure occurs, particularly if the true value of r_int 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 r_int. 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 r_int tends to be less than the individual effects on rH₂O and rCO₂ since both are in the same direction.