Abstract: The contents of inorganic Nitrogen (N) and rates of soil N mineralization at soil depths of 0?5, 5?10,10?20 and 20?30 cm were measured by a field manipulative experiment of ±30% throughfall and closed-top tube incubation method in a Pinus sylvetris var. mongolica plantation at PKU-SOGES, China. The results show that the contents of inorganic N, NH₄⁺-N, and NO₃^--N at the soil depths of 0?30 cm are 6.70±2.31, 5.59±1.78, 1.11±0.77 mg/kg, respectively. There is no significant difference among inorganic N contents of different soil depths and throughfall treatments but the NO₃^--N of +30% is lower than that of control. Net N mineralization rates of 0?30 cm was ?0.24 (?6.65 to 10.24) mg/(kg?30d). Throughfall treatments and soil depths have no significant effects on net ammonification rates. According to the net nitrification rates and net N mineralization rates, both of them at 0?5 cm are significantly higher than those at other soil depths, and treatments of ±30% throughfall are higher than the control. In a word, both the ±30% throughfall treatments decrease inorganic N, and increase net N mineralization rates. The results also indicate that impacts of precipitation change on soil NH₄⁺-N and ammonification are weaker than those on NO₃^--N and nitrification. This study will contribute to assessment of precipitation changes on plantation ecosystem service and N biogeochemical cycle.

Key words: soil nitrogen availability, nitrogen mineralization, precipitation change, soil depth, manipulative experiment, Saihanba

摘要： 在北京大学地球环境与生态系统塞罕坝实验站的樟子松(Pinus sylvestris var. mongolica)人工林内, 采用野外降水控制实验和顶盖埋管法, 在生长季内分0~5, 5~10, 10~20和20~30 cm 4层, 研究穿透雨增加或减少30%对土壤无机氮(铵态氮与硝态氮之和)及净氮矿化速率的影响。结果表明, 樟子松人工林地下0~30 cm无机氮含量为6.70±2.31 mg/kg, 其中铵态氮5.59± 1.78 mg/kg, 硝态氮1.11±0.77 mg/kg。不同土壤深度的无机氮含量无显著差异, 3种穿透雨处理间的土壤铵态氮和无机氮含量无显著差异, 增雨处理的硝态氮含量显著低于对照。0~30 cm的土壤净氮矿化速率为?0.24 (?6.65~10.24) mg/(kg?30d)。穿透雨处理和土壤深度对净氨化速率无显著影响, 0~5 cm的净硝化速率和净氮矿化速率显著高于其余3层, 增雨和减雨处理的净硝化速率和净氮矿化速率显著高于对照。研究结果说明降水变化对土壤铵态氮及氨化作用的影响弱于对硝态氮及硝化作用的影响, 这有助于更准确地评估降水变化对人工林生态系统服务功能和氮素生物地球化学循环过程的影响。

关键词: 土壤氮有效性, 氮矿化, 降水变化, 土壤深度, 控制实验, 塞罕坝地区