The higher area-based photosynthesis in Gossypium hirsutum L. is mostly attributed to higher leaf thickness

There is a trade-off between leaf structures and photosynthesis physiology. While numerous reports have shown a dif- ference in photosynthesis between Gossypium hirsutum L. (upland cotton) and G. barbadense L. (pima cotton), the potential contribution of leaf structures on this difference was not fully clarified. Here, we investigated the differences in area- and mass-based photosynthetic traits and leaf structures between upland and pima cottons. Our results showed that upland cotton had higher area-based net photosynthetic rate (Parea) than that of pima cotton, which was attributed to the coordination of stomatal conductance (gs), area-based mesophyll conductance (gm-area), and maximum carboxylation rate (Vcmax-area). Parea, gm-area, and Vcmax-area correlated positively with leaf mass per area. But upland and pima cotton had similar mass-based PN (Pmass), gm (gm-mass), Vcmax (Vcmax-mass), suggesting that they have a similar photosynthetic capacity of single cells. Consequently, the higher area-based values in upland cotton were only due to a higher leaf thickness (Tleaf).