Controlling growth and carbohydrate utilization of tomato seedlings through day-night temperature difference and high light intensity under elevated CO2 conditions

Negative DIF, increasing nighttime temperature relative to daytime temperature, is widely used in the floral industry to reduce plant height. However, negative DIF can also reduce photosynthetic capacity in vegetative seedlings. We investigated the use of negative DIF combined with high light intensity under elevated CO2 and a long photoperiod to produce compact and well-developed tomato seedlings with reduced plant height. Seedlings were grown for 28 days under positive or negative DIF (with daytime/nighttime temperatures of 25 °C/19 °C or 21 °C/27 °C, respectively) combined with low or high light intensity [250 or 500 μmol m−2 s−1 photosynthetic photon flux density (PPFD), PPFD 250 or PPFD 500, respectively] at 1000 ppm CO2 (mean daily temperature: 23 °C across a photoperiod of 16 h d−1). Compared with positive DIF and PPFD 250, negative DIF with PPFD 500 significantly reduced plant height while tending to increase dry matter (DM) but decrease leaf area (LA). Relative growth rate was decreased under negative DIF despite the provision of PPFD 500, but there were no differences in photosynthetic rate and capacity parameters (e.g., total nitrogen and chlorophyll content at the LA level) between DIF treatments. Negative DIF and PPFD 500 might reduce DM by decreasing the amount of intercepted light in tomato seedlings. Negative DIF and PPFD 500 also increased respiration rate during nighttime and led to the consumption of more nonstructural carbohydrates (NSCs) at the LA level. Overall, our results indicate that negative DIF combined with high light intensity can maintain DM, photosynthetic capacity, and plant development while reducing plant height in tomato seedlings.