Estimation of Photorespiration Based on the Initial Rate of Postillumination CO2 Release

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Abstract
Although open systems have been used for the study of transients in leaf CO2 exchange such as the postillumination burst, these systems frequently do not permit reliable estimates of transient rates due to their nonsteady state nature. A nonsteady state mathematical approach is described which predicts changes in CO2 concentration in the leaf chamber and IR gas analyzer measuring cell as a function of leaf CO2 exchange rate in Nicotiana tabacum cv. John Williams Broadleaf and cv. Havana Seed. With the aid of a computer, a numerical formula simulates the mixing and dilution which occurs as CO2 passes through the finite volume of the measuring cell of the analyzer. The method is presented with special relevance to photorespiration as manifested by the postillumination burst of CO2. The latter is suggested to decline with the 1st order kinetics following darkening of a C3 leaf. This approach provides a basis for reliable estimation of the initial and maximal rate of CO2 evolution during the postillumination burst under a variety of environmental conditions.