Effects of CO2 fertilization on tomato fruit quality under reduced irrigation

CO2 fertilization has been widely used in greenhouse cultivation of tomato (Solanum lycopersicum) to enhance fruit yield; its effects on fruit quality remain largely elusive yet, particularly in combination with reduced irrigation regimes. To explore the response of tomato to the CO2 fertilization under reduced irrigation, tomato (cv. Zhou Si Dun) plants were grown under ambient CO2 (a [CO2],400 ppm) and elevated CO2 (e[CO2], 800 ppm) environment, respectively and subjected to three irrigation levels since anthesis: I1 (irrigated to 90-95 % water holding capacity of the mixture in the pot, WHC), 12 (irrigated to 70-75 % WHC) and 13 (irrigated to 50-55 % WHC). The results showed that fruit yield was significantly higher in plants with I1 than those with 13. Moreover, the e[CO2] enhanced the number of fruit and decreased the percentage of small fruit ( < 70 g), resulting in higher fruit yield as compared to a[CO2]. Leaf area (LA), fruit dry weight (FDW), water use efficiency (WUE), as well as harvest index (HI) were increased under e[CO2], whereas irrigation regime had no influence on FDW, WUE or HI. Both reduced irrigation and e[CO2] increased total soluble solid, vitamin C and lycopene content, while decreased nitrate content in fruit. The results of PCA (Principal Component Analysis) indicated that there was a significant improvement in the comprehensive performance of plants with reduced irrigation at e [CO2] environment. It can be concluded that reduced irrigation, combined with CO2 fertilization, could be a promising strategy to enhance fruit quality in greenhouse tomato production under water-limited conditions.