Sulfate and Nitrate Assimilation in Leaves of Quercus ilex and Quercus pubescens Grown Near Natural CO 2 Springs in Central Italy

L.J. De Kok et al. (eds.), Sulfur Metabolism in Plants, Proceedings of the International Plant Sulfur Workshop 1, DOI 10.1007/978-94-007-4450-9_29, © Springer Science+Business Media Dordrecht 2012 Abstract The effect of long-term exposure to elevated p CO 2 concentrations on sulfate and nitrate assimilation was studied under fi eld conditions using leaves from Quercus ilex and Quercus pubescens trees growing with ambient or elevated CO 2 concentrations in the vicinity of three natural CO 2 springs, Bossoleto, Laiatico and Sulfatara, in Tuscany, Italy. The activity of the key enzymes of sulfate assimilation, adenosine 5 ¢ -phosphosulfate reductase (APR) and nitrate assimilation, nitrate reductase (NR), were measured together with the levels of acid soluble thiols, and soluble non-proteinogenic nitrogen compounds. Whereas NR activity remained unaffected in Q. ilex or increased Q. pubescence , APR activity decreased in the area of CO 2 springs. The latter changes were often accompanied by increased GSH concentrations, apparently synthesized from H 2 S and SO 2 present in the gas mixture emitted from the CO 2 springs. Thus, the diminished APR activity in leaves of Q. ilex and Q. pubescence from spring areas can best be explained by the exposure to gaseous sulfur compounds. Although the concentrations of H 2 S and SO 2 in the gas mixture emitted from the vents at the CO 2 springs were low at the Bossoleto and Laiatico spring, these sulfur gases pose physiological effects, which may override consequences of elevated p CO 2 .