College of Environmental Science and Engineering, Beijing Forestry University, Beijing, 100083, China.
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, A11, Datun Road, Chaoyang District, Beijing, 100101, China.
Chemosphere. 2023 Oct;338:139378. doi: 10.1016/j.chemosphere.2023.139378. Epub 2023 Jul 5.
Increases in soil available nitrogen (N) influence N-cycle gene abundances and emission of nitrous oxide (NO), which is primarily due to N-induced soil acidification in forest. Moreover, the extent of microbial-N saturation could control microbial activity and NO emission. The contributions of N-induced alterations of microbial-N saturation and N-cycle gene abundances to NO emission have rarely been quantified. Here, the mechanism underlying NO emission under N additions (three chemical forms of N, i.e., NO-N, NH-N and NHNO-N, and each at two rates, 50 and 150 kg N ha year, respectively) spanning 2011-2021 was investigated in a temperate forest in Beijing. Results showed NO emissions increased at both low and high N rates of all the three forms compared with control during the whole experiment. However, NO emissions were lower in high rate of NHNO-N and NH-N treatments than the corresponding low N rates in the recent three years. Effects of N on microbial-N saturation and abundances of N-cycle genes were dependent on the N rate and form as well as experimental time. Specifically, negative effects of N on N-cycle gene abundances and positive effects of N on microbial-N saturation were demonstrated in high N rate treatments, particularly with NH addition during 2019-2021. Such effects were associated with soil acidification. A hump-backed trend between microbial-N saturation and NO emissions was observed, suggesting NO emissions decreased with increase of the microbial-N saturation. Furthermore, N-induced decreases in N-cycle gene abundances restrained NO emissions. In particular, the nitrification process, dominated by ammonia-oxidize archaea, is critical to determination of NO emissions in response to the N addition in the temperate forest. We confirmed N addition promoted soil microbial-N saturation and reduced N-cycle gene abundances, which restrained the continuous increase in NO emissions. It is important for understanding the forest-N-microbe nexus under climate change.
土壤有效氮（N）的增加会影响氮循环基因丰度和氧化亚氮（NO）的排放，这主要是由于森林中 N 引起的土壤酸化。此外，微生物氮饱和的程度可以控制微生物活性和 NO 的排放。N 引起的微生物氮饱和和氮循环基因丰度的变化对 NO 排放的贡献很少被量化。在这里，我们研究了 2011 年至 2021 年期间，在北京的一个温带森林中，N 添加（三种 N 的化学形式，即 NO-N、NH-N 和 NHNO-N，每种形式的两个速率，分别为 50 和 150kgNha-1year-1）对 NO 排放的影响。结果表明，与对照相比，所有三种形式的低 N 和高 N 速率下，整个实验过程中 NO 的排放量都增加了。然而，在最近三年中，高 NHNO-N 和 NH-N 处理的 N 速率下，NO 的排放量低于相应的低 N 速率。N 对微生物氮饱和和氮循环基因丰度的影响取决于 N 速率、形式和实验时间。具体而言，在高 N 速率处理中，N 对氮循环基因丰度有负效应，对微生物氮饱和有正效应，特别是在 2019-2021 年添加 NH 时。这些影响与土壤酸化有关。在微生物氮饱和和 NO 排放之间观察到一个驼峰趋势，表明随着微生物氮饱和的增加，NO 排放减少。此外，N 诱导的氮循环基因丰度降低抑制了 NO 的排放。特别是，氨氧化古菌主导的硝化过程对温带森林对 N 添加的响应中 NO 排放的决定至关重要。我们证实，N 添加促进了土壤微生物氮饱和，降低了氮循环基因丰度，从而抑制了 NO 排放的持续增加。这对于理解气候变化下的森林-氮-微生物关系很重要。
