模拟氮沉降对温带阔叶红松林地氮素净矿化量的影响

Effects of Stimulated N Deposition on Soil Net N Mineralization under a Temperate Korean Pine and Broadleaf Mixed Forest

采用埋置PVC管的树脂芯方法原位测定了不同氮形态及其剂量作用下长白山阔叶红松林地0～7cm和0～15cm土壤氮素净氨化、净硝化和净矿化量的季节和年际变化规律。近3年的观测结果表明,对照处理不同土层氮素年净矿化量中以净氨化占主导地位,约占净矿化量的53%～72%,高剂量3NON的输入使该比例减少至37%～66%,而+4NHN的输入却使该比例增至86%～92%。随着模拟氮沉降量增加,土壤氮素年净矿化量也随之增加,尤其外源+4NHN输入对净矿化量的促进作用更为明显,但随着施肥年限的延长,这种促进作用逐渐减弱。与林地0～15cm土壤相比,氮沉降量增加对0～7cm土壤氮素净氨化和净矿化量的促进作用更为明显,尤其是NH4Cl处理的促进作用更大。通过将实验结果与前人报道的野外原位观测整合,逐步回归分析后发现土壤氮素年净矿化量随着氮素年沉降量的增加而增大,氮沉降量对不同区域森林土壤氮素年净矿化量的贡献率约为38%;大气氮沉降量、森林有机层pH及其碳/氮比值可解释不同区域森林表层土壤氮素年净矿化量一半的变化。研究结果将利于有效预测区域林地氮素净矿化量特征及其对环境变化的响应。

Soil samples at 7 cm and 15 cm depths under a Korean pine and broadleafmixed 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 NHaCl. 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.