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Rising CO2 concentrations associated with drought stress is likely to influence not only aboveground growth, but also belowground plant processes. Little is known about root exudation being influenced by elements of climate change. Therefore, this study wanted to clarify whether barley root exudation responds to drought and CO2 enrichment and whether this reaction differs between an old and a recently released malting barley cultivar. Barley plants were grown in pots filled with sand in controlled climate chambers at ambient (380 ppm) or elevated (550 ppm) atmospheric [ CO2] and a normal or reduced water supply. Root exudation patterns were examined at the stem elongation growth stage and when the inflorescences emerged. At both dates, root exudates were analyzed for different compounds such as total free amino acids, proline, potassium, and some phytohormones. Elevated [ CO2] decreased the concentrations in root exudates of some compounds such as total free amino acids, proline, and abscisic acid. Moreover, reduced water supply increased proline, potassium, electric conductivity, and hormone concentrations. In general, the modern cultivar showed higher concentrations of proline and abscisic acid than the old one, but the cultivars responded differentially under elevated CO2. Plant developmental stage had also an impact on the root exudation patterns of barley. Generally, we observed significant effects of CO2 enrichment, watering levels, and, to a lesser extent, cultivar on root exudation. However, we did not find any mitigation of the adverse effects of drought by elevated CO2. Understanding the multitude of relationships within the rhizosphere is an important aspect that has to be taken into consideration in the context of crop performance and carbon balance under conditions of climate change. [ABSTRACT FROM AUTHOR]

Abstract: 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±9μll−1) and elevated (494±16μll−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. [Copyright &y& Elsevier]