A meta-analysis of the combined effects of elevated carbon dioxide and chronic warming on plant %N, protein content and N-uptake rate

Authors: JAYAWARDENA, DILEEPA - University Of Toledo; HECKATHORN, SCOTT - University Of Toledo; Boldt, Jennifer

Submitted to: AoBP (Annals of Botany PLANTS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2021
Publication Date: 5/25/2021
Citation: Jayawardena, D.M., Heckathorn, S.A., Boldt, J.K. 2021. A meta-analysis of the combined effects of elevated carbon dioxide and chronic warming on plant %N, protein content and N-uptake rate. AoBP (Annals of Botany PLANTS). 13(4). Article plab031. https://doi.org/10.1093/aobpla/plab031.
DOI: https://doi.org/10.1093/aobpla/plab031

Interpretive Summary: Elevated carbon dioxide (CO2) concentrations and higher growing temperatures can affect plant growth and nutrition. Researchers have investigated the impact of these two variables, individually and combined, on plant nitrogen concentrations (%N), nitrogen uptake, and protein concentration, but it can be difficult to synthesize the results of all these studies to see what common trends emerge. A meta-analysis allows us to see trends across multiple studies. Data from 58 peer-reviewed, published articles collectively indicate that the plant %N (more so in shoots than roots) and protein concentration will decrease in response to elevated CO2, whereas plant %N will increase in response to elevated temperatures. The combined effect of elevated CO2 and higher temperatures, however, will likely decrease plant %N. Different growth forms reacted differently to these environmental conditions. Plants with a grassy growth form had less of a reduction in shoot %N under elevated CO2 (alone or in combination with elevated temperatures) than woody or non-woody dicots. Non-legumes had less of a reduction in shoot %N under elevated CO2 (alone or in combination with elevated temperatures) than legumes. The meta-analysis analyzed different techniques used for these types of studies; all except greenhouses provided similar results and therefore, greenhouses appear unsuitable for this type of study. This meta-analysis indicates that plant N uptake and metabolism is impacted by rising CO2 concentrations and temperatures, and it provides a framework for which aspects of N metabolism plant breeders can focus improvement efforts on to develop more resilient plants to predicted climate conditions.

Technical Abstract: Elevated CO2 (eCO2) and high temperatures are known to affect plant nitrogen (N) metabolism. Though the combined effects of eCO2 and chronic warming on plant N relations have been studied in some detail, a comprehensive statistical review on this topic is lacking. This meta-analysis examined the effects of eCO2 plus warming on shoot and root %N, tissue protein concentration (root, shoot, and grain), and N-uptake rate. In the analyses, the eCO2 treatment was categorized into two classes (<300 or =300 ppm above ambient or control), the temperature treatment was categorized into three classes (<1.5, 1.5-5, and >5oC above ambient or control), plant species were categorized based on growth form and functional group, and CO2 treatment technique was also investigated. Elevated CO2 alone or in combination with warming reduced shoot %N (more so at =300 vs. <300 ppm above ambient CO2), while root %N was significantly reduced only by eCO2; warming alone often increased shoot %N, but mostly did not affect root %N. Decreased shoot %N with eCO2 alone or eCO2 plus warming was greater for woody and non-woody dicots than for grasses, and for legumes than non-legumes. Though root N-uptake rate was unaffected by eCO2, eCO2 plus warming decreased N-uptake rate, while warming alone increased it. Similar to %N, protein concentration decreased with eCO2 in shoots and grain (but not roots), increased with warming in grain, and decreased with eCO2 and warming in grain. In summary, any benefits of warming to plant N status and root N-uptake rate will generally be offset by negative effects of eCO2. Hence, concomitant increases in CO2 and temperature are likely to negate or decrease the nutritional quality of plant tissue consumed as food by decreasing shoot %N and shoot and/or grain protein concentration, caused, at least in part, by decreased root N-uptake rate.