Nitrogen management under increased atmospheric CO2 concentration in cucumber (Cucumis sativus L.): ameliorating environmental impacts of fertilization

Abstract

In the last years, the atmospheric CO₂ concentration has increased significantly, and this increase can cause changes in various physiological and biochemical processes of plants. However, the response of plants to elevated CO₂ concentration (e[CO₂]) will be different depending on the nitrogen form available and the plant species. Therefore, hydroponic trials on cucumber plants, with two CO₂ concentrations (400 and 1000 ppm) and two nitrogen sources (NO₃^-/NH₄⁺; 100/0 and 90/10), were conducted. Physiological parameters-such as gas exchange, GS, GOGAT and GDH activities, cation composition, soluble sugar and starch content- were measured. The results showed that when plants were grown with NH₄⁺ and e[CO₂], parameters such as photosynthesis rate (A_CO2), instantaneous water use efficiency (WUEi), the content of NH₄⁺, Ca²⁺ and Mg²⁺, and the concentration of starch, were higher than in control plants (irrigated with nitrate as sole nitrogen source and ambient CO₂ concentration (a[CO₂])). Furthermore, an improvement in N assimilation was observed when the GS/GOGAT pathway was enhanced under these conditions (NH₄⁺ and e[CO₂]). Thus, our results contribute to the reduction of the negative environmental impacts of the use of nitrogen fertilizers on this crop, both by reducing nitrogen leakage (eutrophication) and greenhouse gas emissions.