[Mesophyll conductance to CO: Methods and current knowledge].

Mesophyll conductance (g), the total conductance of CO diffusion from substomatal cavity to the site of carboxylation within chloroplast, is a major limiting factor for photosynthesis and a key parameter for improving photosynthetic resource use efficiency of crops. Online C discrimination method is an important method for plant eco-physiological studies and a well-established method for measuring g of C3 plants, although it has not been widely used due to challenges in methodology and high demands on experimental facilities. In this review, we summarized the characteristics of commonly used methods for g, introduced the basic theory of the online C discrimination method, namely Farquhar's photosynthetic C discrimination model; systematically introduced the practical measurements, equations and the components of facilities; and reviewed the drivers for variation in g of C3 plants. At the last part, we discussed the outlook of the development of methodology, new experimental protocols, and applications in measurement scenarios.