Effects of ozone on nitrogen metabolism in the leaves of Fagus crenata seedlings under different soil nitrogen loads

Abstract

To clarify the effects of ozone (O3) on nitrogen (N) metabolism in the leaves of Fagus crenata seedlings under different N loads, the combined effects of O3 and N load on N enzyme activity, amino acid profiles and soluble protein concentrations were investigated. The seedlings were grown in potted andisol supplied with N at 0 (N0), 20 (N20) and 50 kg ha−1 year−1 (N50) and were exposed to charcoal-filtered air or O3 at 1.0, 1.5 and 2.0 times the ambient concentration in open-top chambers from April 2004 to October 2005. The average 24-h concentrations of O3 during the two growing seasons were 11.8, 42.7, 63.3 and 83.7 ppb, respectively. In July 2005, exposure to O3 did not significantly affect the concentration of total free amino acids and activities of nitrite reductase and glutamine synthetase in any N treatment. Exposure to O3 significantly increased the relative content of acidic amino acids in all N treatments while it significantly reduced concentration of total soluble protein (TSP) and ratio of TSP concentration to leaf N concentration in the N50 treatment, but not in the N0 and N20 treatments. Based on the results obtained in the present study, we concluded that exposure to O3 reduces the allocation of N to soluble protein in addition to O3-induced degradation of protein in the leaves of seedlings grown under a relatively high N load, with the result that the degree of O3-induced reduction in the soluble protein was greater under a relatively high N load than under a relatively low N load.