Estimation of Photorespiration Based on the Initial Rate of Postillumination CO(2) Release: I. A Nonsteady State Model for Measurement of CO(2) Exchange Transients.

Although open systems have been used for the study of transients in leaf CO(2) 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 CO(2) concentration in the leaf chamber and infrared gas analyzer measuring cell as a function of leaf CO(2) exchange rate in Nicotiana tabacum vars John Williams Broadleaf and Havana Seed. With the aid of a computer, a numerical formula simulates the mixing and dilution which occurs as CO(2) 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 CO(2). The latter is suggested to decline with the first order kinetics following darkening of a C(3) leaf. This approach provides a basis for reliable estimation of the initial and, hence, maximal rate of CO(2) evolution during the postillumination burst under a variety of environmental conditions.