Ozone and Nitrogen Deposition Effects on Plant Physiology and Growth Vary among Tree Species, Not Plant Functional Types

Rising ozone (O 3 ) concentration and increased nitrogen (N) deposition are global challenges, and it remains unclear whether plant functional types (i.e., deciduous broadleaf vs. evergreen conifer) respond differently to this interactive effect. We investigated the combined effects of O 3 (ambient air with no O 3 filtering, NF; NF + 40 ppb O 3 , NF40; NF + 60 ppb O 3 , NF60) and N addition (no N addition, N0; 50 kg N·hm −2 year −1 , N50; 100 kg N·hm −2 year −1 , N100) on physiological and growth traits in 2 deciduous broadleaf ( Quercus mongolica and Sophora japonica ) and 2 evergreen conifer ( Pinus koraiensis and Pinus bungeana ) tree species. Elevated O 3 induced leaf membrane lipid peroxidation and increased antioxidant enzymatic activities, leading to a significant decrease in photosynthesis and growth, whereas N addition had the opposite effect. Although N and O 3 interacted significantly to modify photosynthesis, N addition did not change the adverse impacts of O 3 on plant growth. The interactive effects on photosynthesis varied depending on the N levels applied, mainly because the inhibition of photosynthesis by O 3 was alleviated by N50 but aggravated by N100. The joint O 3 –N addition effects on plant physiology and growth could not be explained by plant functional types. Instead, there were significant O 3 –N–tree species interactions, implying that the influence of N addition on O 3 -induced negative effects may be determined by the species’ inherent susceptibility to O 3 or their acclimation to N deposition. These results provide an important scientific basis toward the adaptation of forest trees to future increased N deposition and O 3 pollution scenarios.