Free-air CO2 enrichment of wheat: leaf flavonoid concentration throughout the growth cycle

To test the predictions that plants will have a larger flavonoid concentrat ion in a future world with a CO2-enriched atmosphere, wheat (Triticum aesti vum L. cv. Yecora Rojo) was grown in a field experiment using FACE (free-ai r CO2 enrichment) technology under two levels of atmospheric CO2 concentrat ion: ambient (370 pmol mol(-1)) and enriched (550 pmol mol(-1)), and under two levels of irrigation: well-watered (100% replacement of potential evapo transpiration) and half-watered. We also studied the effects of CO2 on the concentration of total non-structural carbohydrates (TNC) and nitrogen (N), two parameters hypothesized to be linked to flavonoid metabolism. Througho ut the growth cycle the concentration of isoorientin, the most abundant fla vonoid, decreased by 62% (from an average of 12.5 mg g(-1) on day of year ( DOY) 41 to an average of 4.8 mg g(-1) on DOY 123), whereas the concentratio n of tricin, another characteristic flavone, increased by two orders of mag nitude (from an average of 0.007 mg g(-1) of isoorientin equivalents on DOY 41 to an average of 0.6 mg g(-1) of isoorientin equivalents on DIOY 123). Although flavonoid concentration was dependent on growth stage, the effects of treatments on phenology did not invalidate the comparisons between trea tments. CO2-enriched plants had higher flavonoid concentrations (14% more i soorientin, an average of 7.0 mg g(-1) for ambient CO2 vs an average of 8.0 mg g(-1) for enriched CO2), higher TNC concentrations and lower N concentr ations in upper canopy leaves throughout the growth cycle. Well-irrigated p lants had higher flavonoid concentrations (11% more isoorientin, an average of 7.1 mg g(-1) for half watered vs an average of 7.9 mg g(-1) for well-wa tered) throughout the growth cycle, whereas the effect of irrigation treatm ents on TNC and N was more variable. These results are in accordance with t he hypotheses that higher carbon availability promoted by CO2-enrichment pr ovides carbon that can be invested in carbon-based secondary compounds such as flavonoids. The rise in atmospheric CO2 may thus indirectly affect whea t-pest relations, alter the pathogen predisposition and improve the UV-B pr otection by changing flavonoid concentrations.