The balance between photosynthetic carbon fixation and leaf respiration drives our expectations of crop performance. The Laisk method is a technique used to estimate the CO2 concentration in the intercellular air space when Rubisco’s oxygenation velocity is inferred to be twice its carboxylation velocity (Ci*) and leaf respiration in the light (RL). These parameters serve as the basis for understanding leaf carbon dynamics at the physiological level and can also be incorporated into global carbon models. While Ci* and RL estimates have been well characterized in model plant species, there is a paucity of information available for horticultural crops. Further, intraspecies variation in these parameters has not been explored. We used the Laisk method to estimate Ci* and RL in three apple rootstock genotypes—G65, G11 and B10. The Laisk method was conducted in the steady-state along with chlorophyll fluorescence measurements to fit the solar induced fluorescence (SIF) model for estimating rates of net assimilation (An). In addition, the Laisk method was conducted in the nonsteady-state using the Dynamic Assimilation Technique (DAT). We found there were no statistically significant differences between genotypes nor technique used for the Laisk method when estimating Ci* and RL across the three genotypes. The findings of this study suggest that Ci* and RL values are conserved within species, the SIF model accurately predicts An for Laisk method data, and the DAT can be used to reliably estimate Ci* and RL.
