An Improvement of Semiempirical Method for Estimating the Total Photosynthesis of the Crop Population : I. On light-photosynthesis curve of rice leaves

摘要

Until none, only one light-photosynthesis (gross) curve which was obtaind at an upper, active leaf was adopted in many mathematical models for estimating the total photosynthesis in the plant population. But, it is well-known that the shape of the light curve in individual leaf constituting the canopy shows some variance according to leaf age. Therefore, in order to improve the semiepirical theory for evaluating the total photosynthesis of rice population, some experiments were made on the shapes of the light curves of individual leaves of rice plants grown under artifiicial population. Results were summarized as follows: 1. The rectangular hyperbola Pg=1/(α+βI) could be fitted satisfactorily to every result of photosynthesis (net photosynthesis plus respiration in the dark) in this experiment, over a wide range of radiation intensity I, by determining the parameters α and β with linear regression in each leaf. 2. Initial slope of the light curve (l/α) was almost constant and independent to the light saturated value (P∞=1/β) which changed accrding to leaf age. 3. It was difficult to express the rate of photosynthsis relative to the P∞ of each leaf with one curve. 4. Then, we defined that the actual light saturating rate of photosynthesis (Pmax) was the point where the slope of the light curve was 0.03 mgCO2/dm2/hr/Klx and named this light intensity, Imax. It was found that the relationship between Imax and Pmax was linear. The standardized light curve which was expressed the values relative to Imax and Pmax of each leaf could be approximated well with one curve of rectangular hyperbola from tillering stage to ripening stage. In other words, the shapes of the light curves to Pmax were similar in various leaves of rice stand. 5. Using this similarity, the simple method to obtatin the light curve showed good fitness to the observed values of photosynthesis.