A Method to Quantify Relative Stomatal, Mesophyll, and Biochemical Limitations to C3 Leaf Photosynthesis in a Specific Growth Environment.

Determining relative limitations of stomatal, mesophyll, and biochemical components (ls, lm, and lb, respectively) to photosynthetic rate (A) can help understand leaf ecophysiology for specific growth conditions. The differential method has been widely applied to estimate the relative limitations in C3 plants, first for comparing two contrasting growth conditions, but also increasingly for a single condition. In addition to the common practical issue that estimating mesophyll conductance is sensitive to measurement noise, the method has a theoretical feature when applied to photosynthesis for a single condition, that is, one of the three in-serial underlying parameters differs from the other two in nature. A new method was proposed, in which a coupled CO2-diffusion and photosynthesis model was fitted to data for A, using intercellular-CO2 and ambient-air-CO2 levels as input, respectively. From two parameter estimates from model-fitting, ls, lm, and lb can be calculated analytically, conditional on that ls + lm + lb = 100%. This method was illustrated using data sets for plants grown under various water, nitrogen, and temperature conditions. The theoretical feature caused the differential method to have a 50% higher estimate of lb and ~25% lower estimate of ls and lm than the new method. Such significant differences were interpreted to result from the differential method defining the limitations in terms of increments in A (dA), whereas the new method defines them in terms of A itself. The measurement noise-sensitive estimation of mesophyll conductance caused an average error of another ~8%. Common misuses and misinterpretations of the differential method were analyzed and discussed.