Supra-optimal daily mean temperature stimulates plant growth and carbohydrate use in tomato

To understand the effects of supra-optimal air temperature with adequate total solar radiation on dry matter production in tomato, we quantified morphological and physiological changes in tomato growth under daily mean temperature at 30 °C. After transplanting, we grew tomato plants under a daily mean temperature of 20 °C, 25 °C, or 30 °C in a growth chamber at high light intensity provided by a LED source until the cumulative daily mean temperature (CT) reached 2000 °C. Plants were pinched when CT reached 1000 °C to remove the vegetative growth sink. Total dry matter was significantly lower at 30 °C than in the other treatments, although relative growth rate (RGR) increased with increasing temperature. An RGR increase at 30 °C was associated with greater net assimilation rate and leaf area ratio. Gross photosynthetic rate and utilization of carbohydrates for plant growth also increased with increasing daily mean temperature. At CT 2000 °C, gas-exchange rate at 30 °C was about twice as high as that at 20 °C, though they were similar at CT 1000 °C in spite of difference of daily mean temperature. Accumulation of non-structural carbohydrates in leaves and stems at 30 °C were less than those at 20 °C. We conclude that supra-optimal daily mean temperature (30 °C) increases RGR, because not only the gas-exchange rate was high, but also photosynthetic assimilates are utilized efficiently for plant growth at 30 °C.