Leaf photosynthesis, plant growth, and carbohydrate accumulation of tomato under different photoperiods and diurnal temperature differences

- Effects of continuous light (CL) with or without a DIF were investigated in tomato.
- CL and zero DIF initially affected different processes in photosynthetic metabolism.
- Thereafter CL and zero DIF had additive negative effects on leaf photosynthesis.
- Such negative effects were reflected in dry matter production at the plant level.
- Severity of CL-induced injury was correlated with nighttime soluble-sugar turnover.

Effects of continuous lighting (CL) with or without a diurnal temperature difference (DIF) on leaf photosynthesis, plant growth and development, and carbohydrate accumulation were investigated with tomato. Plants were grown for four weeks under a photoperiod of 12 h d−1 or CL of 24 h d−1, each combined with a DIF of 10 or 0 °C. Measurements included: leaf net photosynthetic rates, the maximal quantum efficiency of PSII, growth analysis, and quantification of leaf carbohydrates. Severe and moderate CL-induced injury was found on leaves grown under CL with a DIF of 0 and 10 °C, respectively, while it was not observed for plants under 12 h d−1 photoperiod. On the other hand, the apparent severity of the CL-induced injury was not necessarily correlated with leaf net photosynthetic rates. At the initial treatment phase, CL reduced the light-limited photosynthesis while zero DIF reduced the light-saturated photosynthesis, suggesting that CL and zero DIF independently affected different processes in leaf photosynthetic metabolism. Thereafter, CL and zero DIF additively reduced both the light-limited and -saturated photosynthesis. Net photosynthetic rate of leaves under the respective growth conditions were also lowered under CL and/or zero DIF. Such reductions of leaf photosynthesis were reflected in dry matter production at the whole-plant level through decreases in net assimilation rate. Analysis of leaf carbohydrate contents revealed that apparent severity of the CL-induced injury was associated with the diurnal turnover of soluble sugars, suggesting it to be a factor possibly causing the injury.