Background and aims

Natural forest succession may modify soil nitrogen (N) cycling and N gas emissions. However, little is known about how this ecological succession modulates soil N₂O and N₂ emissions. We focused on three typical succession chronsequences of subtropical forests: the early stage of an Alnus nepalensis forest (~ 60 years), the intermediate stage of a Populus bonatii forest (~ 100 years), and the late stage of an evergreen broad-leaved forest (> 300 years).

Methods

The acetylene inhibition technique and molecular method were used to investigate the changing patterns of soil N₂O and N₂ emissions, as well as the key abiotic and biotic factors that regulate gas emissions.

Results

The highest rates of soil N₂O and N₂ emissions were observed in the early-successional stage, which were 10–21 times and 6–12 times higher than those of the intermediate and late stages, respectively. This stimulation in the early stage was mainly related to the pure stands of N-fixing trees, thus amplifying soil inorganic N pools and providing additional substrates for nitrification- and denitrification- driven N₂O. Although N₂O emissions under denitrifying conditions were 2–131 times higher than those under nitrifying conditions, N₂ was the dominant N gas loss in subtropical forests. Changes in nirK-denitrifier abundance with forest succession were closely related to N₂O emissions.

Conclusion

Our findings suggest that variations in soil active nitrogen pools and nirK abundance associated with subtropical forest succession could reduce N₂O and N₂ emissions, thus resulting in positive feedbacks for climate change mitigation.

中文翻译：

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亚热带森林演替过程中土壤 N2O 和 N2 排放量减少

 背景和目标

天然林演替可能会改变土壤氮 (N) 循环和氮气排放。然而，人们对这种生态演替如何调节土壤 N ₂ O 和 N ₂排放知之甚少。我们重点研究了亚热带森林的三个典型演替年代：尼泊尔桤木林的早期阶段（约60年）、博纳蒂杨林的中期阶段（约100年）和常绿阔叶林的晚期阶段（> 300 年）。

 方法

采用乙炔抑制技术和分子方法研究了土壤N ₂ O和N ₂排放变化规律，以及调节气体排放的关键非生物和生物因素。

 结果

土壤N ₂ O和N ₂排放速率在演替早期最高，分别是中期和后期的10~21倍和6~12倍。早期的这种刺激主要与固氮树木的纯林有关，从而扩大了土壤无机氮库，为硝化和反硝化驱动的N ₂ O提供了额外的底物。尽管反硝化条件下的N ₂ O排放量为2 –N ₂是亚热带森林中主要的氮气损失，比硝化条件下高出 131 倍。 nirK反硝化菌丰度随森林演替的变化与N ₂ O排放密切相关。

 结论

我们的研究结果表明，与亚热带森林演替相关的土壤活性氮库和nirK丰度的变化可以减少 N ₂ O 和 N ₂排放，从而对减缓气候变化产生积极的反馈。