The effect of simulated N deposition on concentration of soil base cations and net N mineralization was studied in Acer velutinum Bioss. plantation in Hyrcanian forest, North Iran. Nine plots were established in May 2015 and three N addition treatments were designed: N0 (control), N1 (50 kg N ha −1 year −1), and N2 (100 kg N ha −1 year −1), respectively. NH 4 NO 3 solution was monthly sprayed on the forest floor during 1 year starting from May 2015. Soil pH, EC, organic carbon (OC), and concentrations of total N, NO − 3 , NH þ 4 , phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were measured. Nitrogen treatments significantly decreased soil pH and EC. The concentration of N in N2 was significantly greater than N0 (control). Compared to N0, the soil P, K, Ca, and Mg decreased in N treatments, but soil OC, NO − 3 , and NH þ 4 increased. Net N mineralization rates were positive but showed no significant difference between treatments. As the first work in Iranian Hyrcanian forests, this study showed that the concentration of soil nutrients can be changed under N additions in this area, and these new results can be considered as suitable data for predicting and modeling future trees' growth and forest ecosystems' production in Hyrcanian forests.

Key message Nitrogen (N) addition (10 and 15 g N m −2 year −1 as dissolved 4 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. • ConclusionThe 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.

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