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  • Title: Photosynthetic activity in relation to a gradient of leaf nitrogen content within a canopy of Siebold's beech and Japanese oak saplings under elevated ozone.
    Author: Watanabe M, Hoshika Y, Inada N, Koike T.
    Journal: Sci Total Environ; 2018 Sep 15; 636():1455-1462. PubMed ID: 29913605.
    Abstract:
    The primary objective of this study was to describe parameters related to the leaf biochemical assimilation capacity of photosynthesis, such as the maximum rates of carboxylation (Vcmax) and electron transport (Jmax), as a function of the leaf nitrogen content throughout a canopy of Siebold's beech and Japanese oak grown under elevated ozone (O3) conditions during a growing season. To this end, we investigated the relationship between photosynthetic traits and leaf nitrogen content in various canopy positions of two tree species under free-air O3 exposure (60 nmol mol-1, during daylight hours) in June, August, and October 2012. We observed O3-induced reduction in Vcmax and Jmax without reduction of leaf nitrogen content in both tree species. In Siebold's beech, Vcmax and Jmax in leaves with higher Narea were largely decreased by O3 from August, while little effect of O3 was observed in leaves with lower Narea. On the other hand, there was no difference in the extent of O3-induced reduction in Vcmax and Jmax across the range of Narea in leaves of Japanese oak. Reduction of leaf nitrogen content under elevated O3 conditions was observed only in Siebold's beech in October. These results indicated that the decrease in the efficiency of photosynthetic nitrogen use is in an earlier step in O3-induced decline of photosynthesis in Siebold's beech and Japanese oak. Based on these results, we emphasize the importance of integration of O3 effects into the conventional estimation of Vcmax and Jmax from leaf nitrogen content for evaluating canopy photosynthesis under current and future elevated O3 conditions.
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