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CO2 Effects on Micronutrients in Plants
Reference
Natali, S.M., Saņudo-Wilhelmy, S.A. and Lerdau, M.T. 2009. Plant and soil mediation of elevated CO2 impacts on trace metals. Ecosystems 12: 715-727.

Background
The authors write that Loladze (2002) suggests "there will be a decrease in all soil-derived nutrients in plants, because the increase in atmospheric CO2 is not matched by an increase in soil-derived elements," which state of affairs, according to Loladze, could lead to a reduction in the nutritive quality of plant foliage and fruit. However, they note that this hypothesis may well be wrong, because "increased production of fine roots with CO2 enrichment (Norby et al., 2004; Pritchard et al., 2008) may allow plants to match increased carbon assimilation with increased uptake of soil-derived elements."

What was done
To explore these contrasting views of the subject, Natali et al. "examined CO2 effects of a suite of metal micronutrients and contaminants in forest trees and soils at two free-air CO2 enrichment sites -- a loblolly pine forest in North Carolina (Duke) and a sweetgum plantation in Tennessee [Oak Ridge National Laboratory (ORNL)] -- and an open-top chamber experiment in a scrub-oak community in Florida [Smithsonian Environmental Research Center (SERC)]."

What was learned
The three U.S. researchers report that they "did not find an overall decline in foliar metal concentrations with CO2 enrichment," but that they did find that dilution effects for metal micronutrients were generally "less than for non-essential trace metals," and that "some essential plant metals were greater under elevated CO2 (for example, 28% increase in Mn across species and sites)."

What it means
Natali et al. conclude that their results "should alleviate some concerns that rising CO2 concentrations will result in broad-scale decreases in the concentrations of all elements essential for plant function and animal nutrition," as proposed by Loladze (2002). They also say their generally opposite results for non-essential trace elements (some of which can be toxic) "may be applicable to contaminated systems," stating that "elevated CO2 may, through dilution effects, alleviate aluminum toxicity." In general, therefore, one could say that elevated CO2 tends to increase the availability of helpful trace elements, while it tends to decrease the availability of harmful ones.

References
Loladze, I. 2002. Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry? Trends in Ecology and Evolution 17: 457-461.

Norby, R.J., Ledford, J., Reilly, C.D., Miller, N.E. and O'Neill, E.G. 2004. Fine-root production dominates response of a deciduous forest to atmospheric CO2 enrichment. Proceedings of the National Academy of Sciences, USA 101: 9689-9693.

Pritchard, S.G., Strand, A.E., McCormack, M.L., Davis, M.A., Finzi, A., Jackson, R.B., Matamala, R., Rogers, H.H. and Oren, R. 2008. Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study. Global Change Biology 14: 588-602.

Reviewed 9 December 2009