Elevated atmospheric CO2 (eCO2) concentration initially enhances photosynthesis, growth and ecosystem productivity, but the excessive use of nitrogen due to the increased productivity causes uncertainty in long-term ecosystem responses. We exposed Korean red pine, Chinese ash, and Korean mountain ash to current atmospheric CO2 concentration (aCO2), 1.4 times higher CO2 concentration (eCO21.4), and 1.8 times higher CO2 concentration (eCO21.8) in an Open-Top Chamber (OTC) experiment for eight years (2010-2017) to investigate the effect on the morphological and physiological properties of trees. We also assessed whether nitrogen limitation occurred with time by comparing leaf and soil nitrogen concentration. CO2 fertilization effect was observed on tree growth for the first two years (p < 0.05), but there was no difference thereafter. For photosynthetic properties, CO2 effects were species-specific; no effects on Korean red pine and Chinese ash vs. significant effect on Korean mountain ash. However, maximum photosynthetic and carboxylation rates significantly decreased by 24.3% and 31.3% from 2013 to 2017, respectively. Leaf nitrogen significantly decreased by 21.0 % at eCO21.4 and 18.5 % at eCO21.8 compared with aCO2 treatment. This study showed the decline of leaf nitrogen and species-specific responses to long-term high CO2 concentration, which will effect on species competition and ecosystem succession.
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