Elevated and super-elevated CO 2 differ in their interactive effects with nitrogen availability on fruit yield and quality of cucumber.

Background: Elevated carbon dioxide (CO ₂ ) 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 CO ₂ concentrations - 400 (ambient CO ₂ ), 800 (elevated CO ₂ , eCO ₂ ) and 1200 µmol mol ^-1 (super-elevated CO ₂ ) - and two N applications - 0.06 (low N) and 0.24 g N kg ^-1 soil (high N).
Results: Compared with ambient CO ₂ , eCO ₂ 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 CO ₂ reduced the carbon allocation to fruits thus yield increase (71%). Additionally, eCO ₂ 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 eCO ₂ , super-elevated CO ₂ can still improve the fruit quality to some extent in low N availability.
Conclusions: Elevated CO ₂ 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.
(© 2018 Society of Chemical Industry.)