Optimal coordination and reorganization of photosynthetic properties in C4grasses

C 3 and C 4 are major functional types in terrestrial biosphere models, with photosynthesis traits as important input parameters. The evolution of C 4 required reorganizations of Calvin-Benson-cycle and coordination of C 4 -cycle enzymes, resulting in divergences of physiological traits between C 3 and C 4 . In addition, photosynthesis further optimized after the evolution of C 4 causing diversification within C 4 lineages due to different evolutionary histories. We combined optimality modeling, physiological measurements and phylogenetic analysis to examine how various aspects of C 4 photosynthetic machinery were reorganized and coordinated within C 4 lineages and as compared to closely-related C 3 in grasses. Optimality models and measurements indicated a higher maximal electron transport to maximal Rubisco carboxylation ratio ( J max / V cmax ) in C 4 than C 3 , consistent with the optimal prediction to maximize photosynthesis. The coordination between Calvin-Benson and C 4 cycles ( V pmax / V cmax ), however, is in line with the optimal modeling results under 200 ppm, as opposed to current CO 2 . Such inconsistencies can be explained by a slowly declining assimilation rate beyond optimal V pmax / V cmax . Although rapid coordination occurred early in C 4 evolution, C 4 is still under optimizing processes and photosynthetic measures have continued to increase across time. Lastly, better understandings of J max / V cmax , V pmax / V cmax and fluorescence-based-electron-transport proffer enhanced approaches to parameterize terrestrial biosphere models.