模拟氮沉降降低亚热带米槠天然林土壤氧化亚氮排放潜势

我国亚热带地区大气氮沉降量逐年上升,对森林土壤生物地球化学循环造成严重影响。本研究设置了对照(不添加氮)、低氮(40 kg·hm^-2·a^-1)和高氮(80 kg·hm^-2·a^-1)处理,分析了亚热带米槠天然林土壤反硝化功能基因丰度和N₂O排放潜势对氮沉降的响应。结果表明: 高氮处理显著降低土壤N₂O排放潜势。长期(8年)氮沉降对nirS、nirK、nosZ Ⅰ和nosZ Ⅱ基因丰度均无显著影响,但nosZ Ⅰ丰度均显著高于nosZ Ⅱ丰度,表明nosZ Ⅰ在酸性森林土壤中占主导。与对照相比,高氮处理显著降低(nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ)值。(nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ)值与土壤pH值呈显著正相关。长期高氮沉降可能通过降低土壤pH值使得土壤(nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ)值下降,从而降低森林土壤N₂O排放潜势。

Simulated nitrogen deposition reduces potential nitrous oxide emissions in a natural Castanopsis carlesii forest soil

The reactive nitrogen deposition in subtropical region of China has been increasing annually, which affects biogeochemical processes in forest soils. In this study, three treatments were established, including control (no N addition, CK), low nitrogen deposition (40 kg·hm^-2·a^-1, LN), and high nitrogen deposition (80 kg·hm^-2·a^-1, HN) to study the response of denitrifying functional genes and potential N₂O emissions to simulated nitrogen deposition in the soils of a natural Castanopsis carlesii forest. Results showed that HN significantly decreased soil potential N₂O emission, while 8-year nitrogen deposition did not affect the abundances of nirS, nirK, nosZ Ⅰ and nosZ Ⅱ. However, the abundance of nosZ Ⅰwas significantly higher than nosZ Ⅱ in all the treatments, indicating that nosZ Ⅰ dominated over nosZ Ⅱ in the acidic soils. HN significantly decreased the ratio of (nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ), which was positively correlated with soil pH. The results suggested that long-term high nitrogen deposition reduced soil pH and the abundance ratio of (nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ), which subsequently reduced the potential N₂O emission.