CO2-Induced Changes in Wheat Grain Composition: Meta-Analysis and Response Functions

Abstract

Elevated carbon dioxide (eCO 2 ) stimulates wheat grain yield, but simultaneously reduces protein/nitrogen (N) concentration. Also, other essential nutrients are subject to change. This study is a synthesis of wheat experiments with eCO 2 , estimating the effects on N, minerals (B, Ca, Cd, Fe, K, Mg, Mn, Na, P, S, Zn), and starch. The analysis was performed by (i) deriving response functions to assess the gradual change in element concentration with increasing CO 2 concentration, (ii) meta-analysis to test the average magnitude and significance of observed effects, and (iii) relating CO 2 effects on minerals to effects on N and grain yield. Responses ranged from zero to strong negative effects of eCO 2 on mineral concentration, with the largest reductions for the nutritionally important elements of N, Fe, S, Zn, and Mg. Together with the positive but small and non-significant effect on starch concentration, the large variation in effects suggests that CO 2 -induced responses cannot be explained only by a simple dilution model. To explain the observed pattern, uptake and transport mechanisms may have to be considered, along with the link of different elements to N uptake. Our study shows that eCO 2 has a significant effect on wheat grain stoichiometry, with implications for human nutrition in a world of rising CO 2 .

Nitrogen application is required to realize wheat yield stimulation by elevated CO2 but will not remove the CO2‐induced reduction in grain protein concentration

“…The mechanisms of the highly consistent CO 2 ‐induced reduction in GPC over a wide range of studies in different crops such as wheat, barley, rice, potato and oilseed rape (Bahrami et al, ; Broberg et al, ; Dier et al, ; Högy & Fangmeier, ; Högy et al, ; Loladze, ; Myers et al, ; Taub et al, ) have recently been much discussed in the literature. In this study, we observed that the negative effect of eCO 2 on GPC did not depend on N application rate.…”

“…The world is likely to face problems with nourishment (nutrient) rather than feeding (food energy) over the coming decades (Haddad et al, ). Thus, the effect by eCO 2 to consistently reduce crop concentrations of protein and other nutrients (Broberg et al, ) and the fact that the effects on GPC persist at high N application rates is a major concern for agriculture under global change. One should also keep in mind that the biggest concerns around reduced nutrients from eCO 2 are in comparatively poor areas of the world where N rates are relatively low, while high N rates are mostly typical of wealthier farming systems.…”

“…Elevated CO 2 (eCO 2 ) is known to stimulate photosynthesis and yield in many C 3 crops (Leakey et al, ; Ziska & Bunce, ) including wheat, Triticum aestivum (Amthor, ). Effect of eCO 2 on crops is considered one of the main aspects of global change affecting agriculture over the coming century (Lobell & Gourdji, ), not only by its effect on yield magnitude, but also because of its negative effects on the grain protein concentration (GPC) as well as concentration of other mineral nutrients in crops (Beleggia et al, ; Broberg, Högy, & Pleijel, ; Högy & Fangmeier, ; Loladze, ; Myers et al, ; Taub, Miller, & Allen, ; Uddling, Broberg, Feng, & Pleijel, ).…”

Rising Atmospheric CO2 Lowers Concentrations of Plant Carotenoids Essential to Human Health: A Meta‐Analysis

“…The pervasiveness of CO 2 ‐driven declines in plant minerals becomes evident only in studies achieving a high statistical power . For example, while calcium and sulfur were reported to both significantly increase and decrease in the grains of wheat grown under eCO 2 over several seasons, larger scale individual and meta‐analytic CO 2 studies reported only declines for calcium and sulfur (and most other minerals) in wheat grains . Hence, notwithstanding the variability and inconsistency of responses of various minerals often reported in small‐powered CO 2 studies, the global impact of rising CO 2 on plant minerals overall is negative, widespread throughout latitudes, and systemic throughout plant tissues …”

“…However, as a rule, eCO 2 alters multiple physiological processes in plants, making it extremely unlikely for the dilution by carbohydrates to act alone. A simple but rigorous stoichiometric argument based on the elemental mass‐balance shows that rising CO 2 should affect plant minerals negatively but the effect should be “nonuniform across elements.” Indeed, high‐powered eCO 2 studies find that some minerals (e.g., magnesium) consistently decline stronger relative to other elements (e.g., manganese) . However, the simplicity of the stoichiometric argument applicable to the plant ionome (all the minerals and trace elements in the plant), breaks down for complex substances such as carotenoids because, unlike minerals, they can be synthesized and decomposed within plants, which significantly complicates mass‐balance equations.…”