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item Idso, Sherwood
item RIBAS, A
item Kimball, Bruce

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Many studies of the effects of atmospheric CO2 enrichment on leaf tissue composition have revealed significant reductions in the concentrations of certain essential elements, such as nitrogen, which is needed for the formation of chlorophyll and the construction of important leaf proteins. However, most of these experiments have been of relatively short duration; and there is reason to believe that, given enough time, plants may be able to gradually adjust to a significant increase in the air's CO2 content and restore their leaf mineral concentrations to levels similar to those characteristic of today's atmosphere. In a test of this hypothesis, we measured the concentrations of twelve leaf minerals from month 30 to month 85 of a long-term CO2 enrichment study of sour orange trees. At the start of our measurements, the concentrations of four leaf minerals, including nitrogen, were from 15 to 25% lower in the CO2-enriched trees than they were in trees exposed to normal air. By month 85, however, concentrations were essentially identical in both sets of trees. This finding demonstrates that certain plant processes take very long times to acclimate or adjust to a change in the air's CO2 content, and that atmospheric CO2 enrichment -- especially at the rate at which the CO2 content of earth's atmosphere is currently rising -- does not necessarily lead to a reduction in the nutritive quality of leaf tissue, which bodes well for the future health of all life that ultimately depend on earth's vegetation for its sustenance.

Technical Abstract: Leaf mineral content and specific leaf area (SLA) of sour orange trees were measured at bimonthly intervals throughout years 3 through 7 of a long-term study of the effects of a 300 micro mol mol-1 enrichment of the air's CO2 content under conditions of high nutrient and water supply. There were clear seasonal trends in the concentrations of most of the studied elements, as well as in SLA. In addition, although total mineral content per tree was always larger for all elements at elevated CO2, there were significant initial decreases in SLA and the leaf concentrations of the xylem-mobile, phloem-immobile elements Mn, N Ca and Mg, as well as a significant sustained increase in the leaf concentration of B, but no changes in the concentrations of K, Fe, Na, P, S, Zn and Cu. Interestingly, the initial reductions in the leaf concentrations of Mn, N, Ca and Mg gradually disappeared over the years, indicating a positive acclimation to elevated CO2.