Modelling photosynthetic light-response curve in Calotropis procera under salinity or water deficit stress using non-linear models

In the present study, the photosynthetic light-response curves (PLR curves) of the wild shrub Calotropis procera were determined under water deficit or salinity stressed plants. The Thornley and Marshall & Biscoe non-linear models were tested in order to investigate which model better describes the photosynthetic light-response curve. When no constraints were exerted on dark respiration values, Thornley model was a better fit. However, when the measured dark respiration values were forced into the model, the PLR curve fits well to Marshall & Biscoe model. The latter gave more pronounced effects of water deficit or salinity stress on the PLR curve parameters such as maximum gross photosynthesis Pgmax, apparent quantum efficiency α and the convexity θ of the curve. The features of both above mentioned mathematical models to describe the photosynthetic light-response curve of Calotropis plant are discussed.