Nitrogen management under increased atmospheric CO2 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.