Effect of nitrogen addition on soil CO2 efflux and fine root biomass in maple monocultures of the hyrcanian region

• Key message Nitrogen (N) addition (10 and 15 g N m −2 year −1 as dissolved N H 4 N 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. • Context The effect of increased atmospheric Nitrogen (N) deposition on forest soil CO 2 efflux is still unclear in the Hyrcanian forests and has received considerable attention in the context of global climate change. • Aims Aims of this study were to determine how soil CO 2 efflux and fine root biomass change after N addition in a maple (Acer velutinum Bioss.) plantation. • Methods 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 NH 4 NO 3 solution was sprayed monthly below the trees’ canopy for 1 year. Soil temperature, moisture, and soil CO 2 efflux were measured monthly with static dark closed chambers. Fine root biomass was seasonally measured by soil sampling at the same depth. • Results Soil temperature, moisture, and soil CO 2 efflux were affected by different levels of N addition. Soil CO 2 efflux significantly increased with N addition, and N3 displayed the highest rate (174 ± 16.1 mg CO 2- C m −2 h −1 ). Fine root biomass increased significantly in N3. • Conclusion 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.