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 (ACO2), 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.
Highlights
The atmospheric carbon dioxide (CO2) concentration is increasing at a faster rate and is projected to reach nearly 1000 μmol mol−1 by the end of 2 1001
The decrease was more pronounced when the plants were irrigated with the 100/0 treatment at both CO2
Our data showed that the combination of different N forms (NO3−/NH4+) and e[CO2] provoked a significant increase in the gas exchange parameters
Summary
The atmospheric carbon dioxide (CO2) concentration is increasing at a faster rate and is projected to reach nearly 1000 μmol mol−1 by the end of 2 1001. The response of plants to e[CO2] varies depending on other environmental factors[3], such as the nitrogen form ( NO3− or NH4+) available[4]. Authors such as Rubio-Asensio and B loom[4] reported that plants irrigated with NH4+ showed a more positive response to e[CO2], than those irrigated with N O3−, as e[CO2] inhibited the assimilation of N O3− in the shoots of C3 plants. The responses of plants were assessed by measuring the net CO2 assimilation, internal C O2 concentration, instantaneous water use efficiency, cation concentration, nitrogen-metabolizing enzymes, starch, and soluble sugars
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