喀斯特原生乔木林和次生林土壤氮矿化特征

Characteristics of soil nitrogen mineralization in a Karst primary forest and a secondary forest

【目的】探究喀斯特森林土壤氮矿化特征及供氮能力。【方法】以贵州喀斯特原生乔木林和次生林为研究对象,采用树脂芯法,原位连续培养测定土壤氮矿化/硝化动态特征。【结果】(1)喀斯特原生乔木林和次生林土壤无机氮含量随培养时间延长存在明显的变化,NH_4^+-N含量呈先增加后减少再增加趋势,NO-3-N含量表现为总体增加趋势。NH_4^+-N是土壤有效氮的主要存在形式,其含量占土壤无机氮的84.57%~94.31%。(2)两演替群落土壤氮矿化速率呈"V"形变化,范围分别为-0.43~0.97 mg/(kg·d)和-0.91~1.43 mg/(kg·d);硝化速率呈波动上升趋势,范围分别为0.21~0.49 mg/(kg·d)和0.03~0.31 mg/(kg·d)。(3)原生乔木林土壤无机氮含量、矿化速率、氨化速率和硝化速率均高于次生林。(4)原生乔木林土壤氮全年净矿化总量170.82 kg/(hm^2·a),是次生林的2.48倍,两种林分土壤净硝化氮分别占净矿化氮的95%和100%。【结论】喀斯特森林土壤供氮能力较强,但土壤氮矿化过程中氮硝化占主导,表明土壤中植物可利用的氮素易于淋溶或挥发损失。

[ Objective ] This study explored the characteristics of nitrogen （N） mineralization and nitrogen supply capacity in a Karst primary forest and a secondary forest. [ Method ] A Karst primary forest and a secondary forest were chosen as study sites. Temporal variations in soil N mineralization and nitrification were determined in situ by continuous incubation by using the resin-core method. [ Resuh ] ① With an increase in incubation time, the content of soil inorganic N in both the primary forest and the secondary forest showed pronounced variation. The NH4^＋-N contents firstly increased, then decreased and finally increased, while NO3^--N contents generally increased. The NH4^＋-N was the main form of inor- ganic N, and accounted for 84. 57%-94. 31% of the soil inorganic nitrogen. ② The mineralization rate had a ＇ V＇ shape, and its ranges in primary forest and secondary forest were -0. 43-0. 97 mg/（ kg. d） and -0. 91-1.43 mg/（ kg· d）, respectively. Nitrification rates tended to increase, and were 0. 21-0. 49 mg/（ kg.d）, 0.03-0. 31 mg/（ kg ·d）, respectively. ③ The inorganic N content and rates of net nitrogen mineralization, nitrification, and ammonification in the primary forest were higher than those in the secondary forest. ④ The annual net amount of N mineralization was 170. 82 kg/（hm^2·a） in the Karst primary forest, 2. 48 times that in the secondary forest. Nitrified N in the primary forest and the secondary forest were 95% and 100%, respectively, of mineralized N. [ Conclusion] The soil in the Karst forest had a relatively high capacity for supplying N, and soil nitrification played a dominant role in the process of soil N mineraliza- tion, indicating that the available N was volatile or easy to leach.