Effect of weather parameters on photosynthesis in four castor bean genotypes

Field experiments on rainfed castor were conducted during two consecutive years to study the individual and combined effects of weather parameters, viz. vapour pressure deficit (VPD), light intensity (LI) and temperature on net photosynthetic rate (Pn). Response of net photosynthetic rate to low and high regimes of these weather parameters was also studied. The study indicated that Pn is positively correlated with LI and negatively with VPD. Predictability of net photosynthetic rate in all the genotypes increased many folds by considering the combined effect of light and vapour pressure deficit. Interactive effects of weather parameters on net photosynthetic rate showed that the adverse effect of higher vapour pressure deficit was more aggravated under either higher light intensity or temperature regimes than under lower light intensity or temperature regimes. The positive effect of LI on Pn was stronger under lower VPD and lower temperature conditions than under higher VPD and higher temperature conditions. Temperature showed significant adverse effect only under either higher LI or higher VPD regimes.