NUTRIENT DILUTION BY STARCH IN CO2-ENRICHED CHRYSANTHEMUM

Increasing growth irradiance and CO2 generally decreases foliar nutrient concentration on a dry weight basis and increases foliar starch concentration. However, the extent to which starch concentrations 'dilute' foliar nutrient concentrations when the latter are expressed on a dry weight basis is not known. To determine the importance of differential starch accumulation in calculating nutrient concentrations on a dry weight basis, leaf nutrient and starch concentrations were measured in Chrysanthemum x morifolium 'Fiesta' (Ramat.) cuttings grown at three irradiance levels and two CO2 levels for eight weeks in both winter and spring. On a dry weight basis, foliar concentrations of most nutrients were lower in both seasons as a result of the elevated CO2 and irradiance levels, and total dry weights were higher. Per cent starch was greater at the high CO, level in both seasons but was only greater at higher irradiances in the winter experiment. When starch was subtracted from the leaf dry weights, the differences between CO2 and irradiance treatments disappeared with respect to N, P, K, Ca, Mg, S, and B but not for Fe, Mn, Zn, and Cu.