Photosynthetic Responses of × 'Red' under Different Light Conditions.

Light is an essential energy source for plant photosynthesis, although it can also be a stress-causing element. Therefore, the current research was aimed to compare photosynthetic responses of × 'Red' leaves at different positions (bottom old leaf, 1; center mature leaf, 2; top expanded leaf, 3) established under three photosynthetic photon flux densities (PPFDs): 550 μmol·m·s as high (H), 350 μmol·m·s as medium (M), and 255 μmol·m·s as low (L). After six months, all the replicates were relocated to interior rooms with a PPFD of 30 μmol·m·s. There were no significant differences in chlorophyll concentration of the old leaf among treatments, before (Day 0) and after shifting the plants to interior rooms (Day 30). The total chlorophyll concentrations of the mature and top leaves increased significantly. In greenhouse conditions, H and M treatments did not show any significant change for net photosynthetic rate (n) at various leaf positions. However, M2 exhibited an improved n in the interior conditions. Plants grown under M treatment were greener and had bigger leaves compared to other treatments. Our study reveals that × 'Red' photosynthesis responses to different light conditions varied distinctly. However, M treatment can keep the plants looking green by accumulating enough energy for indoor conditions, and middle and lower leaves may be triggered to restore photosynthetic activity under low light or indoor conditions.