Light response curves for gas exchange characteristics were developed for spur leaves of `Stayman' and `Delicious' apple (Malus domestica Borkh.) from interior, intermediate, and exterior canopy positions throughout the season. At full bloom (FB), before full leaf expansion, exterior leaves had higher maximum rates of net photosynthesis (Pn), and a statistically different Pn light response curve than the interior leaves. Intermediate leaves had intermediate Pn rates and light response curves. Pn light response curves for all three `Delicious' canopy positions differed from each other from FB + 6 weeks until the end of the season. Interior leaves had maximum Pn rates of only 50% to 60% of those for the exterior leaves from FB + 10 weeks until the end of the season. Light saturation levels were higher for the exterior leaves than for interior or intermediate leaves. Exterior leaves had a tendency throughout the season for higher quantum efficiency of Pn at subsaturating light levels than interior or intermediate leaves. Stomatal conductance was higher for the exterior than the interior or intermediate leaves of `Delicious' on all dates. Water-use efficiency was equivalent among all leaves. Exterior leaves had higher specific leaf weight, dark respiration rates, and incident light levels on all dates than interior or intermediate leaves.
shading treatments. Light response of chlorophyll fluorescence LED light. After 4 weeks of light acclimation, light response curves of chlorophyll fluorescence were taken under LED light inside a growth chamber (E15; Conviron, Winnipeg, Canada). A custom
parameters, and light response curves. The photosynthetic light responses of the four cultivars were determined between the months of May and July during three sampling periods: 1) BH, 2) during PH, and 3) when nearly all or all fruit had naturally fallen
curves of the adaxial side of mature leaves showed that the photosynthetic rate increased with increasing PPFD , but there were no differences among light qualities ( Fig. 2A ). Although light–photosynthetic response curves of blue and green LEDs on the
. At higher FR light doses, neither increased intensity nor duration was effective as the hypocotyl elongation response had reached saturation. The saturation response curve, expressed with a Michaelis-Menten-type model, estimated FR light doses
concentration. In both Boldt et al. (2014) and Erwin and Gesick (2017) , CO 2 concentration was maintained at 400 µmol·mol −1 for the light response curves, and PPFD was maintained at 300 µmol·m −2 ·s −1 for the CO 2 response curves. Therefore, data
stage. The overall difference in g l between treatments was smaller during the reproductive growth stage than that during the vegetative growth stage. Photosynthetic light response. The photosynthetic light response curves during the vegetative growth
threshold and among the DLI underneath the light bar, DLI sun , and the average daily duty cycle. Simulation of the effects on photosynthesis. To quantify the relationship among sunlight, supplement light, and A n , we used A n − PPF response curves for
, light is not only a source to regulate flower initiation but also acts as a direct energy resource for photosynthetic accumulation ( Kinet, 1977 ). It has been established that the light intensity and light interception by the plant canopy directly leads
described previously. Light response (A N -Q) curves were developed using one representative plant from each experimental unit. Using a light-emitting diode light source, leaves were exposed to the following incremental levels of PAR : 2000, 1500, 1000, 500