Effect of nitrogen addition on soil CO 2 efflux and fine root biomass in maple monocultures of the hyrcanian region

Nitrogen (N) addition (10 and 15 g N m −2 year −1 as dissolved $${\mathbf{N}\mathbf{H}}_{4}{\mathbf{N}\mathbf{O}}_{3}$$ ) significantly increased the CO 2 efflux from the forest soil and the fine root biomass in a maple (Acer velutinum Bioss.) plantation. Following a seasonal pattern, soil CO 2 efflux showed an exponential relationship with the fine root biomass and soil temperature. The effect of increased atmospheric Nitrogen (N) deposition on forest soil CO2 efflux is still unclear in the Hyrcanian forests and has received considerable attention in the context of global climate change. Aims of this study were to determine how soil CO2 efflux and fine root biomass change after N addition in a maple (Acer velutinum Bioss.) plantation. Since the wet N deposition in these areas is 3–5 g N m−2 year−1, four treatments including N1 (5 g N m−2 year−1), N2 (10 g N m−2 year−1), N3 (15 g N m−2 year−1), and N0 (control) were selected. Twelve plots (10 × 20 m) were established, and a $${\mathrm{NH}}_{4}{\mathrm{NO}}_{3}$$ solution was sprayed monthly below the trees’ canopy for 1 year. Soil temperature, moisture, and soil CO2 efflux were measured monthly with static dark closed chambers. Fine root biomass was seasonally measured by soil sampling at the same depth. Soil temperature, moisture, and soil CO2 efflux were affected by different levels of N addition. Soil CO2 efflux significantly increased with N addition, and N3 displayed the highest rate (174 ± 16.1 mg CO2-C m−2 h−1). Fine root biomass increased significantly in N3. The predicted levels of N deposition in such plantations will probably lead to enhanced CO2 efflux from soils in reforested areas close to industrial sites in the Hyrcanian forest.