Modeling Leaf Photosynthesis of Evening Primrose Crop (Oenothera spp).

Introduction. Evening primrose plant is considered a novae crop. Its tine seeds contain oil rich in alpha-linoleic acid which is been used for pharmaceutical uses and is increasingly gaining a place in the market. Many physiological aspects of this crop are yet unknown. The objectives were to characterize and to model the leaf photosynthesis of this crop considering as factors the light intensity, the nitrogen applications and the plant cycle. Materials and methods. Photosynthesis was measured on growing leaves from plants planted in pots. A Ciras 2 Portable Photosynthesis System and a Parkinson auto-control leaf chamber were used for these measurements. The light intensity was changed from 0 to 1800  µmol PPFD m^-2 s^-1. The nitrogen applications were 0, 80 and 160 kg ha^-1. The measurements were done at all the development phases of this crop. Results. There was found a defined relationship between the leaf photosynthesis and all the three factors. Leaf photosynthesis fitted the quadratic photosynthesis equation as a function of the light intensity. There was also observed a defined relationship between the development phases (as growing degree-days) and the photosynthesis efficiency (φ) and the leaf asymptote light saturated rate (Amax) coefficients, which are terms of the quadratic photosynthesis equation. There was also found a defined relationship between Amax and the nitrogen applications. Mathematic equations were developed for φ and Amax coefficients as a function of the growing degree-days and the nitrogen applications. Conclusions. Leaf photosynthesis of evening primrose plant was defined by the light intensity, the development phases and the nitrogen applications. The leaf photosynthesis can be modelled by the quadratic photosynthesis equation, and the equations for the photosynthesis efficiency and the leaf asymptote light saturated rate coefficients as function of the light intensity, de growing-degree days and the nitrogen applications.