Diurnal changes in the stomatal, mesophyll, and biochemical limitations of photosynthesis in well-watered greenhouse-grown strawberries

The diurnal variations in the factors of photosynthesis reduction under well-watered greenhouse conditions remain poorly understood. We conducted diurnal measurements of gas exchange and chlorophyll fluorescence in strawberries (Fragaria × ananassa Duch.) for three sunny days. Quantitative limitation analysis was also conducted to investigate the diurnal variations of photosynthetic limitations [stomatal (SL), mesophyll (MCL), and biochemical limitation (BL)]. Under well-watered greenhouse conditions, a photosynthesis reduction was observed, and the respective limitations exhibited different diurnal changes based on the environmental stress severity. The main limitation was SL, varying between 11.3 and 27.1% around midday, whereas MCL and BL were in 4.3-14.2% and 1.7-8.5%, respectively, under relatively moderate conditions. However, both SL (11.2-34.2%) and MCL (4.8-26.4%) predominantly limited photosynthesis under relatively severe conditions, suggesting that stomatal closure was the main limitation and that the decline in mesophyll conductance was not negligible under strong environmental stress, even under well-watered greenhouse conditions.