EFFECTS OF SEASON LONG CO2 ENRICHMENT ON CEREALS .2. NUTRIENT CONCENTRATIONS AND GRAIN QUALITY

Two cultivars each of spring wheat (Triticum aestivum L., cv. Star and cv. Turbo) and spring barley (Hordeum vulgare L., cv. Alexis and cv. Arena) were exposed season-long to ambient (384 p.p.m.) and above ambient CO2 concentrations (551, 718 p.p.m.) in open-top chambers. Plant samples were taken at the booting stage and at maturity. Concentrations (grams per gram dry weight) of macro (Ca, K, Mg, N, P, S) and micronutrients (Fe, Mn, Zn) were measured in stems, leaves, ears and grains, and the amino acid composition of the grain protein was determined. For most nutrients studied the sequence and size of the response of the four cereal plants to the CO, enrichment was cv. Arena < cv. Alexis < cv. Turbo < cv. Star. The CO2 enrichment usually produced a decrease in nutrient concentrations, which was already detectable at the booting stage and was further enhanced until plant maturity. Nutrient concentrations of straw were more affected than those of grains. The decrease in concentration was greatest for N followed by Mg, Ca and K, and the maximum decrease as compared with ambient CO2 amounted to 43%, 35%, 33% and 21% for straw, and 30%, 13%, 28% and - 6% for grains. Concentrations of micronutrients were also found to be partially decreased by about 10-30%. At 718 p.p.m. CO, grain protein concentrations were 96% (cv. Arena), 85% (cv. Alexis), 72% (cv. Turbo) and 70% (cv. Star) of the ambient CO2 value, however, the index of essential amino acids was increased. Overall, the CO2 enrichment did not decrease the nutrient harvest index of all nutrients except of sulphur. Nutrient use efficiency increased by high CO2 levels for cv. Star and cv. Turbo and decreased for cv. Arena.