Effects of shading and carbon dioxide concentration on growth dynamics and partitioning of fresh and dry weight in tomato

Year-round cultivation of tomatoes in the cold region in western Tohoku district (the sea of Japan region), particularly in Akita prefecture, is difficult due to low sunlight conditions and low air temperatures between December and March. This study investigated such challenges for growers through a 24-h and long-term monitoring of tomatoes grown under different sunlight conditions (30 and 70% shading of sunlight) and carbon dioxide concentration (ambient carbon dioxide and maintain 1,200 ppm). Leaf number, shoot length, and stem diameter did not differ between environmental conditions; however, leaf area was greater under 70% shading compared to 30% shading, which became even greater under higher carbon dioxide treatment. The total fresh weight of tomato plants continued to decrease during the day, even with adequate irrigation, but increased at night for every treatment. Furthermore, the fresh and dry weights of fruits under 70% shading were the same or larger than those under 30% shading with or without extra carbon dioxide. These results were attributed to a greater loss of water in tomato plants through transpiration from larger leaves compared to water uptake in roots, imposing a form of drought stress during the day. As a result, the distribution of water and dry matter to the fruit was the same or higher under 70% shading than under 30% shading. Future work examining the differences in sap content between leaves and fruits and the rate of photosynthesis in different environments, will be examined.