Abstract:

Increasing global nitrogen deposition can affect nutrient cycling in terrestrial ecosystems and profoundly influence forest soil nutrients and nitrogen mineralization rates.A typical Larix gmelinii var.principis-rupprechtii (Mayr)Pilg.plantations in the northern Yanshan Mountains were selected as the study site.A simulation nitrogen(N)deposition experiment was conducted with seven N addition levels of 0,5,10,20,40,80,and 160 kg/(hm²·a),designated T0,T5,T10,T20,T40,T80,and T160,respectively.The effects of N addition on soil nutrients and N mineralization rates were analyzed after three years of treatment.The results showed that:1)Simulated nitrogen deposition significantly affected soil ${\mathrm{N}\mathrm{O}}_{3}^{-}$-N content,with significant differences between T160 and T5,T10,and T20 treatments(P<0.05).2)With increasing N addition,soil net N ammonification rate,net N nitrification rate,and net N mineralization rate initially increased and then decreased.The turning points of the net N nitrification rate and net N mineralization rate were both more than 80 kg/(hm²·a)(R²=0.92,P<0.01;R²=0.93,P<0.01).Soil gross N ammonification rate decrease with increasing N addition(R²=0.67,P>0.05),while gross N nitrification rate initially increased and then decreased,with a turning point>80 kg/(hm²·a)(R²=0.81,P<0.05).3)The main soilfactors affecting the net N ammonification rate were ${\mathrm{N}\mathrm{O}}_{3}^{-}$-N,pH,and total phosphorus(TP),whereas those affecting the net nitrification rate were ${\mathrm{N}\mathrm{O}}_{3}^{-}$-N content,C∶P,and N∶P.The nonlinear response of soil N mineralization rates to N addition provides a theoretical basis for predicting dynamic changes in soil N mineralization rates under N deposition.

Key words: simulated nitrogen deposition, soil nutrients, nitrogen mineralization rate, nitrogen addition