Abstract
Abstract The increasing [CO 2 ] 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 [CO 2 ] (e[CO 2 ]) 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[CO 2 ] concentration (≥550 μmol/mol) compared to ambient [CO 2 ] (a[CO 2 ]) concentration (≤380 μmol/mol). Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] 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 [CO 2 ] enrichment (FACE). However, the integration of the influence of reporting bias did not affect the significance or the direction of the [CO 2 ] effects.
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Claims 13
Claim · model-written summary
Elevated CO2 reduced grain protein concentration of wheat by about 5%–10%.
- Taxon
- wheat
Triticum aestivume2 - Treatment
- e[CO2]e1
- Outcome
- protein concentrationse2
- Direction
- reductionse2
- Value
- ~5%–10%e2
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced grain Zn and Fe concentrations of wheat by about 3%–12%.
- Taxon
- wheatTriticum aestivume2
- Treatment
- e[CO2]e1
- Outcome
- Zn and Fe concentrationse2
- Direction
- reductionse2
- Value
- ~3%–12%e2
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced grain protein concentration of rice by about 5%–10%.
- Taxon
- rice
Oryza sativae2 - Treatment
- e[CO2]e1
- Outcome
- protein concentrationse2
- Direction
- reductionse2
- Value
- ~5%–10%e2
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced grain Zn and Fe concentrations of rice by about 3%–12%.
- Taxon
- riceOryza sativae2
- Treatment
- e[CO2]e1
- Outcome
- Zn and Fe concentrationse2
- Direction
- reductionse2
- Value
- ~3%–12%e2
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 decreased grain protein concentration of field peas by 1.7%.
Verbatim
e3“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced grain Zn and Fe concentrations of field peas by about 4%–10%.
Verbatim
e3“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced grain protein, Zn and Fe concentrations of corn by about 5%–10%.
- Taxon
- corn
Zea mays subsp. mayse3 - Treatment
- e[CO2]e1
- Outcome
- protein, Zn, and Fe concentrationse3
- Direction
- reductionse3
- Value
- ~5%–10%e3
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 gave a small, nonsignificant increase of 0.37% in soybean grain protein under medium N and dry water.
- Taxon
- soybean
Glycine maxe3 - Treatment
- e[CO2]e1
- Outcome
- protein concentratione3
- Direction
- increasee3
- Value
- 0.37%e3
- Qualifier
- medium N and dry watere3
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 reduced soybean grain Zn and Fe concentrations by about 2%–5%.
- Taxon
- soybeanGlycine maxe3
- Treatment
- e[CO2]e1
- Outcome
- Zn and Fe concentrationse3
- Direction
- reducede3
- Value
- ~2%–5%e3
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
Elevated CO2 gave a nonsignificant increase in soybean grain Fe concentration under medium N and wet conditions.
- Taxon
- soybeanGlycine maxe2
- Treatment
- e[CO2]e1
- Outcome
- Fe concentratione2
- Direction
- increasee2
- Qualifier
- medium N and wet conditionse2
- Comparator
- ambient [CO 2 ]e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“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%”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
e6“compared to ambient [CO 2 ] (a[CO 2 ]) concentration”
Claim · model-written summary
The responses of grain protein, Zn and Fe concentrations to elevated CO2 were modified by water stress and N.
- Taxon
- major food cropse0
- Treatment
- water stress and Ne1
- Outcome
- responses of protein, Zn, and Fe concentrationse1
Not reportedDirection
Verbatim
e0“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[CO 2 ] concentration”
e1“Grain protein, Zn, and Fe concentrations were reduced under e[CO 2 ]; however, the responses of protein, Zn, and Fe concentrations to e[CO 2 ] were modified by water stress and N”
Claim · model-written summary
Published meta-analyses of crop responses to FACE show medium levels of bias.
Verbatim
e0“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[CO 2 ] concentration”
e4“there are medium levels of bias within published”
Claim · model-written summary
Integrating reporting bias did not change the significance or direction of the CO2 effects.
Verbatim
e0“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[CO 2 ] concentration”
e5“did not affect the significance or the direction of the [CO 2 ] effects”
The same questions in other papers
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See all 27 papers →8 of 9 groups shown: named compounds and organisms first, then groups whose results differ (checked claim by claim), then those with positive and negative results, then the smaller groups.
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.