Abstract
The increasing [CO2] in the atmosphere increases crop productivity. However, grain quality of cereals and pulses are substantially decreased and consequently compromise human health. Meta‐analysis techniques were employed to investigate the effect of elevated [CO2] (e[CO2]) on protein, zinc (Zn), and iron (Fe) concentrations of major food crops (542 experimental observations from 135 studies) including wheat, rice, soybean, field peas, and corn considering different levels of water and nitrogen (N). Each crop, except soybean, had decreased protein, Zn, and Fe concentrations when grown at e[CO2] concentration (≥550 μmol/mol) compared to ambient [CO2] (a[CO2]) concentration (≤380 μmol/mol). Grain protein, Zn, and Fe concentrations were reduced under e[CO2]; however, the responses of protein, Zn, and Fe concentrations to e[CO2] were modified by water stress and N. There was an increase in Fe concentration in soybean under medium N and wet conditions but nonsignificant. The reductions in protein concentrations for wheat and rice were ~5%–10%, and the reductions in Zn and Fe concentrations were ~3%–12%. For soybean, there was a small and nonsignificant increase of 0.37% in its protein concentration under medium N and dry water, while Zn and Fe concentrations were reduced by ~2%–5%. The protein concentration of field peas decreased by 1.7%, and the reductions in Zn and Fe concentrations were ~4%–10%. The reductions in protein, Zn, and Fe concentrations of corn were ~5%–10%. Bias in the dataset was assessed using a regression test and rank correlation. The analysis indicated that there are medium levels of bias within published meta‐analysis studies of crops responses to free‐air [CO2] enrichment (FACE). However, the integration of the influence of reporting bias did not affect the significance or the direction of the [CO2] effects.
Highlights
Climate change factors, including high temperature and atmospheric CO2 concentration ([CO2]), are among the most pervasive environ‐ mental changes (Mueller et al, 2016)
There is very limited understanding of how grain protein, Zn, and Fe respond to e[CO2] under a range of stress conditions, water and nitrogen limitations
A meta‐analysis has been carried out to analyze the effect of e[CO2] on protein, zinc, and iron for five different crops under different func‐ tional groups considering different levels of water and N
Summary
In 2017, a database of the effect of [CO2], temperature, and ni‐ trogen on grain protein and grain yield was created (Al‐Hadeethi et al, 2017). This study focused on investigating grain protein, Zn, and Fe for wheat, rice, soybean, corn, and field peas in Australia, Japan, United States, and Germany under two different levels of [CO2] (ambient and elevated), three levels of nitrogen (low, medium, and high), and two levels of water (wet and dry). Elevated [CO2] resulted in a small and nonsignificant reduction in protein concentra‐ tion (2.69%) under medium N level, but a greater and significant re‐ duction in protein concentration (9.36%) under high N. Effect of elevated [CO2] and water on crop protein and nonsignificant reduction in the protein concentration in field peas was observed under e[CO2] (1.75%). The protein concentration decreased significantly under medium N (11.61%) but there was no significant reduction under low N (2.9%). The protein concentration showed a nonsignificant decrease under wet conditions (0.02%) and a non‐ significant increase under dry conditions (1.22%). Elevated [CO2] decreased the Fe concentration in field peas (4.44%)
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