Effects of free-air CO₂ enrichment on energy traits and seed quality of oilseed rape

Previous experiments have not considered in situ evaluations of CO₂ enrichment on oilseed rape (OSR) under European climates with regard to energetic value and seed quality. Therefore, Brassica napus cv. Campino was grown in a free-air CO₂ enrichment (FACE) field experiment at Stuttgart-Hohenheim (Germany) under ambient (388 ± 9 μl l−1) and elevated (494 ± 16 μl l−1) CO₂ concentrations. Aboveground biomass production and energy yields of both straw and seeds increased, while energy contents per dry weight were identical in both CO₂ treatments. Among the mineral concentrations in seeds, sulphur, boron and cadmium were significantly reduced and zinc and manganese tended to decrease (0.1 ≥ P > 0.05) under elevated CO₂. Total protein concentration declined significantly by 4.6% with CO₂ enrichment, although increased seed yield (+18.4%) compensated for the change on a production basis. Accordingly, several proteinogenic amino acids per unit meal weight were significantly reduced (asparagine/aspartic acid, glycine, alanine, cysteine, valine, isoleucine, and leucine) or tended to decrease (glutamine/glutamic acid, methionine) in the high-CO₂ treatment, resulting in higher carbon/nitrogen ratios. Amino acids on a per protein basis and total oil concentrations were unaffected, while oil yield per unit ground area tended to increase by 19.8%. Elevated CO₂ slightly changed the composition of fatty acids on a per dry weight basis, which was more pronounced for unsaturated fatty acids. The concentration of major unsaturated fatty acids such as oleic acid increased significantly, while linolenic acid, nervonic acid and the group of essential fatty acids were decreased. There was also a negative trend for cis-11-eicosenic acid. The same holds true for the composition of fatty acids on a per oil basis. Among glucosinolates, only progoitrin tended to decrease under CO₂ enrichment. The results indicate that elevated CO₂ levels may have implications for food and feed quality and use for industrial processing of OSR in the future.