The process that the evolution from C₃towards C₄photosynthesis is driven

Compared to the plants with C 3 photosynthesis, the plants with C 4 photosynthesis have higher light, water, and nitrogen use efficiencies. Though only 3% of higher plants have C 4 photosynthesis, C 4 photosynthesis contribute about 23% of terrestrial gross primary productivity. Currently, it remains elusive how the procedure of the evolution from C 3 towards C 4 photosynthesis is driven. Here, Flaveria genus, the chief model for C 4 evolutionary researches, was used to study this driving through a combined analysis of ecological, physiological and biochemical data. From proto-Kranz to C 4 -like, results showed that precipitation was negatively associated with the activity of C 4 metabolic core enzyme and C 4 flux, respectively. With increased vein density, an increased temperature and precipitation were observed during the earlier evolutionary stage. Our study indicated that decreasing precipitation and increasing temperature accompanied the transition from C 3 to C 2 photosynthesis and further transition from C 2 to developing C 4 photosynthesis. There was a positive relationship between CO 2 compensation point, stomatal density and precipitation, supporting the notion that decreasing precipitation enhances photorespiration through reducing stomatal conductance during the evolution. As the driving force from proto-Kranz to C 4 -like, our study highlights that drought dominated rather than heat during C 4 evolution. This study suggests that the driving force between certain stages during the evolution towards C 4 photosynthesis are different and increased water availability should be needed in the initial phase.