Elevated and super-elevated CO2 differ in their interactive effects with nitrogen availability on fruit yield and quality of cucumber.

BACKGROUND: Elevated carbon dioxide (CO2 ) and nitrogen (N) availability can interactively promote cucumber yield, but how the yield increase is realized remains unclear, whilst the interactive effects on fruit quality are unknown. In this study, cucumber plants (Cucumis sativus L. cv. Jinmei No. 3) were grown in a paddy soil under three CO2 concentrations - 400 (ambient CO2 ), 800 (elevated CO2 , eCO2 ) and 1200 µmol mol-1 (super-elevated CO2 ) - and two N applications - 0.06 (low N) and 0.24 g N kg-1 soil (high N). RESULTS: Compared with ambient CO2 , eCO2 increased yield by 106% in high N but the increase in total biomass was only 33%. This can result from greater carbon translocation to fruits from other organs, indicated by the increased biomass allocation from stems and leaves, particularly source leaves, to fruits and the decreased concentrations of fructose and glucose in source leaves. Super-elevated CO2 reduced the carbon allocation to fruits thus yield increase (71%). Additionally, eCO2 also increased the concentrations of fructose and glucose in fruits, maintained the concentrations of dietary fiber, phosphorus, potassium, calcium, magnesium, sulfur, manganese, copper, molybdenum and sodium, whilst it decreased the concentrations of nitrate, protein, iron, and zinc in high N. Compared with eCO2 , super-elevated CO2 can still improve the fruit quality to some extent in low N availability. CONCLUSIONS: Elevated CO2 promotes cucumber yield largely by carbon allocation from source leaves to fruits in high N availability. Besides a dilution effect, carbon allocation to fruits, carbohydrate transformation, and nutrient uptake and assimilation can affect the fruit quality. © 2018 Society of Chemical Industry.