Effects of Stimulated N Deposition on Soil Net N Mineralization under a Temperate Korean Pine and Broadleaf Mixed Forest
模拟氮沉降对温带阔叶红松林地氮素净矿化量的影响

Soil samples at 7 cm and 15 cm depths under a Korean pine and broadleaf mixed forest at Changbai Moun- tain, Northeast China, were collected with PVC tubes with resin cores at bases to study seasonal and annual changes in soil net N ammonification, net N nitrification, and net N mineralization after the addition of N sources such as (NH4)2SO4, NH4Cl, and KNO3. In the non-fertilized plots, net N ammonification of the soils at both depths accounted for 53%-72% of soil net N mineralization, whereas the ratio of soil net N ammonification to net N mineralization was re- duced by 37%-66% in the KNO3 added soils at a high dose, and the ratio was increased by 86%-92% in the NH4+-N treated soils. The addition of N sources, particularly NH4+-N, appeared to increase soil net N mineralization, and the stimulating effect reduced with time of fertilization. Both net N ammonification and net N mineralization rates of the soils at the 7 cm depth were greater than those of the soils at the 15 cm depth, particularly after the addition of NH4Cl. In combination with results of previous studies, stepwise regression analysis showed that 38% of the variability in annual net N mineralization of forest soils at various global sites could be attributed to the annual wet atmospheric N deposition. In addition, 50% of the variability in annual soil net N mineralization could be attributed to the annual wet atmospheric N deposition, the pH value of forest organic horizon, and the ratio of total C to total N. The results are beneficial for pre- dicting soil net N mineralization at regional forest stands and its responses to environmental changes.