Nitrogen Fertilization Modified the Responses of Schima superba Seedlings to Elevated CO(2) in Subtropical China

There are very few studies about the effects of relatively higher CO(2) concentration (e.g., 1000 μmol·mol(−1)) or plus N fertilization on woody plants. In this study, Schima superba seedings were exposed to ambient or eCO(2) (550, 750, and 1000 μmol·mol(−1)) and N fertilization (0 and 10 g·m(−2)·yr(−1), hereafter: low N, high N, respectively) for one growth season to explore the potential responses in a subtropical site with low soil N availability. N fertilization strongly increased leaf mass-based N by 118.38%, 116.68%, 106.78%, and 138.95%, respectively, in different CO(2) treatments and decreased starch, with a half reduction in leaf C:N ratio. Leaf N was significantly decreased by eCO(2) in both low N and high N treatments, and N fertilization stimulated the decrease of leaf N and mitigated the increase of leaf C:N by eCO(2). In low N treatments, photosynthetic rate (Pn) was maximized at 733 μmol·mol(−1) CO(2) in August and September, while, in high N treatments, Pn was continuously increased with elevation of CO(2). N fertilization significantly increased plant biomass especially at highly elevated CO(2), although no response of biomass to eCO(2) alone. These findings indicated that N fertilization would modify the response of S. superba to eCO(2).