Abstract
The models used to describe the light response of electron transport rate in photosynthesis play a crucial role in determining two key parameters i.e., the maximum electron transport rate (J (max)) and the saturation light intensity (I (sat)). However, not all models accurately fit J-I curves, and determine the values of J (max) and I (sat). Here, three models, namely the double exponential (DE) model, the non-rectangular hyperbolic (NRH) model, and a mechanistic model developed by one of the coauthors (Z-P Ye) and his coworkers (referred to as the mechanistic model), were compared in terms of their ability to fit J-I curves and estimate J (max) and I (sat). Here, we apply these three models to a series of previously collected Chl a fluorescence data from seven photosynthetic organisms, grown under different conditions. Our results show that the mechanistic model performed well in describing the J-I curves, regardless of whether photoinhibition/dynamic down-regulation of photosystem II (PSII) occurs. Moreover, both J (max) and I (sat) estimated by this model are in very good agreement with the measured data. On the contrary, although the DE model simulates quite well the J-I curve for the species studied, it significantly overestimates both the J (max) of Amaranthus hypochondriacus and the I (sat) of Microcystis aeruginosa grown under NH(4) (+)-N supply. More importantly, the light intensity required to achieve the potential maximum of J (J (s)) estimated by this model exceeds the unexpected high value of 10(5) μmol photons m(-2) s(-1) for Triticum aestivum and A. hypochondriacus. The NRH model fails to characterize the J-I curves with dynamic down-regulation/photoinhibition for Abies alba, Oryza sativa and M. aeruginosa. In addition, this model also significantly overestimates the values of J (max) for T. aestivum at 21% O(2) and A. hypochondriacus grown under normal condition, and significantly underestimates the values of J (max) for M. aeruginosa grown under NO(3) (-)N supply. Our study provides evidence that the 'mechanistic model' is much more suitable than both the DE and NRH models in fitting the J-I curves and in estimating the photosynthetic parameters. This is a powerful tool for studying light harvesting properties and the dynamic down-regulation of PSII/photoinhibition.