Ammonium nitrogen combined with partial root-zone drying enhanced fruit quality of tomato under elevated atmospheric CO2

Increasing nitrogen fertilization and reduced irrigation regimes can alleviate the negative effect of elevated CO2 (e[CO2]) on fruit quality of tomatoes, yet little is known about the effects of N forms combined with partial rootzone drying irrigation (PRI) on tomato growth and fruit quality under e[CO2]. This study aimed to investigate the response of tomato plants to N forms, PRI and their interactions under e[CO2]. Tomato plants (Solanum lycopersicum L.) were grown in split-root pots in climate-controlled growth chambers with CO2 concentration of 400 ppm and 800 ppm, respectively, supplied with two N forms i.e. nitrate nitrogen (NN) and ammonium nitrogen (AN). Three irrigation regimes, i.e. full irrigation (FI), deficit irrigation (DI) and PRI were applied from anthesis to fruit maturity. The results showed that e[CO2] decreased plant water use (WU) while increased biomass accumulation (Delta DW), water use efficiency (WUE) and fruit number (FN). Under e[CO2], AN plants had less Delta DW, leaf area and WU while similar yield, as compared with NN plants. Additionally, under e[CO2] with PRI treatment, AN fruits had greater [N], [K], [N/P], and soluble solid (Brix) to acid ratio, but lower [C/N], [P/K] and acid concentration, and similar fruit [C], [P], [Ca], [Mg] and [S], in comparison with the NN fruits. Collectively, AN treatment combined with PRI under e[CO2] improved fruit mineral nutrition and the flavor of tomato fruits without reduction in yield and WUE. Therefore, AN combined with PRI could be an alternative strategy to improve tomato fruit quality in future drier and CO2-enriched environment.