Nitrogen management under increased atmospheric CO(2) concentration in cucumber (Cucumis sativus L.): ameliorating environmental impacts of fertilization

In the last years, the atmospheric CO(2) 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 CO(2) concentration (e[CO(2)]) will be different depending on the nitrogen form available and the plant species. Therefore, hydroponic trials on cucumber plants, with two CO(2) concentrations (400 and 1000 ppm) and two nitrogen sources (NO(3)(−)/NH(4)(+); 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 NH(4)(+) and e[CO(2)], parameters such as photosynthesis rate (A(CO2)), instantaneous water use efficiency (WUEi), the content of NH(4)(+), Ca(2+) and Mg(2+), and the concentration of starch, were higher than in control plants (irrigated with nitrate as sole nitrogen source and ambient CO(2) concentration (a[CO(2)])). Furthermore, an improvement in N assimilation was observed when the GS/GOGAT pathway was enhanced under these conditions (NH(4)(+) and e[CO(2)]). 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.