Effects of ozone on leaf nitrogen assimilation and nitrogen utilization in photosynthetic apparatus of Fagus crenata seedlings grown under different atmospheric CO2 and soil nitrogen conditions

Ozone (O 3 ) impairs photosynthesis and growth of plants, depending on atmospheric CO 2 and soil N levels. Previously, we found that CO 2 exposure mitigated O 3 -induced reduction in maximum carboxylation rate ( V cmax ) of Fagus crenata seedlings in September. This effect was more pronounced with soil N supply in July. To better understand these physiological mechanisms, we investigated leaf N assimilation and its utilization in the photosynthetic apparatus of F. crenata seedlings. Seedlings were grown with two O 3 levels (low and twice ambient), two CO 2 levels (ambient and 700 µmol mol −1 ), and three soil N levels (0, 50, and 100 kg N ha −1 year −1 ). CO 2 exposure mitigated the negative effects of O 3 on ribulose bisphosphate carboxylase/oxygenase (Rubisco) concentration rather than on the ratio of V cmax to Rubisco concentration in September. Furthermore, such mitigative effects tended to be more pronounced with soil N supply in July, although a three-factor interaction among O 3 , CO 2 , and soil N was not statistically significant. Additionally, in July and September, the degrees of O 3 -induced changes in Rubisco concentration under each CO 2 and N treatment composition were similar to those of the ratio of Rubisco concentration to total soluble protein (TSP) concentration and leaf N allocation to Rubisco, in contrast to the TSP concentration and N assimilation process. Therefore, changes in the N utilization characteristics as proteins involved in the photosynthetic apparatus and the Rubisco quantity in response to O 3 , CO 2 , and soil N could cause the interactive effect on the V cmax of F. crenata seedlings. • We studied O 3 , CO 2 , and soil N effects on N utilization for photosynthesis in leaves. • O 3 -induced reduction in Rubisco conc. was mitigated by CO 2 and exacerbated by soil N. • The CO 2 -mitigated O 3 effect on Rubisco conc. tended to be greater under higher soil N. • Reduction in Rubisco conc. by O 3 corelated to that in maximum carboxylation rate. • Cause of reduction in Rubisco conc. by O 3 was change in N utilization for protein.