Effects of ozone exposure on sub-tropical evergreen Cinnamomum camphora seedlings grown in different nitrogen loads

Abstract

The present study aims in investigating the individual and combined effects of ozone (O3) exposure and nitrogen (N) load on the growth and photosynthetic characters of Cinnamomum camphora seedlings, a dominant evergreen broadleaf tree species in sub-tropical regions. The seedlings were supplied with N as NH4NO3 solution at 0, 30 and 60 kg ha−1 year−1 (simplified as N0, N30, N60, respectively) and were exposed to ambient O3 concentration (AA) or elevated [O3] (E-O3, AA +60 ppb) for one growth season. E-O3 induced significant negative effects on foliar photosynthesis, including lower photosynthetic rate, reduced carboxylation efficiency, quantum yield of PSII and photosynthetic pigment contents, despite no effect on growth. In contrast, N load acted as fertilization effects. Medium N (N30) increased photosynthetic pigments and stem-base diameter growth relative to N0, whereas high N load (N60) significantly enhanced the growth, photosynthetic pigments, and dark and light action of photosynthesis of C. camphora seedlings. No significant interactive effects of O3 and N load on the growth, net photosynthetic rate and pigment contents of the seedlings were found, suggesting that N supply to the soil at ≤60 kg ha−1 year−1 does not significantly change the sensitivity of C. camphora to ozone.