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

摘要

To clarify the effects of ozone (O) on nitrogen (N) metabolism in the leaves of Fagus crenata seedlings under different N loads, the combined effects of O 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 hap# yearp# (N50) and were exposed to charcoal-filtered air or O 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 O during the two growing seasons were 11.8, 42.7, 63.3 and 83.7 ppb, respectively. In July 2005, exposure to O 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 O 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 O reduces the allocation of N to soluble protein in addition to O-induced degradation of protein in the leaves of seedlings grown under a relatively high N load, with the result that the degree of O-induced reduction in the soluble protein was greater under a relatively high N load than under a relatively low N load.