Warm root‐zone temperature ensures the mineral concentrations in cucumber plants under elevated [CO2] by improving the migration pathways of mineral elements from the soil to plants

Background The mineral nutrient concentrations in plants are usually decreased under elevated CO2 concentration ([CO2]), while warm root‐zone temperature (RZT) can improve plant growth and the absorption of mineral nutrients in plants. Aims The effects of RZT on the growth and mineral nutrient concentrations in cucumber (Cucumis sativus L.) plants were investigated under different [CO2] levels. Methods A soil‐cultured pot experiment was carried out on cucumber plants under two [CO2] levels (ambient and elevated) and two RZT levels (cold and warm) in four open‐top chambers. Results Although elevated [CO2] promoted root growth, it did not counteract the decrease in the concentration of nitrogen ([N]), potassium ([K]), calcium ([Ca]), and magnesium ([Mg]) in cucumber plants due to the decreased mass flow indicated by the decreased transpiration rate (Tr) under cold RZT. In comparison, warm RZT increased the [N], [K], [Ca], and [Mg] in cucumber plants under elevated [CO2], attributed to a higher Tr and better root growth. In addition, the concentration of phosphorus ([P]), iron ([Fe]), manganese ([Mn]), and zinc ([Zn]) in cucumber plants was maintained or increased under elevated [CO2] by the promoted root growth related to interception by warm RZT. Conclusions Under elevated [CO2], warm RZT could ensure the [N], [K], [Ca], and [Mg] in cucumber plants mainly by increasing the Tr and improving the root growth. Whereas warm RZT maintained or increased [P], [Fe], [Mn], and [Zn] primarily relied on the improved interception as indicated by the better root growth.