Kazmi Fahad Ali, Mander Ülo, Ranniku Reti, Öpik Maarja, Püssa Kersti, Soosaar Kaido, Kasak Kuno, Masta Mohit, Ah-Peng Claudine, Espenberg Mikk
Department of Geography, University of Tartu, 51003, Tartu, Estonia.
Department of Biological and Agricultural Engineering, University of Arkansas, Fayetteville, AR, 72701, USA.
Sci Rep. 2025 Jul 25;15(1):27155. doi: 10.1038/s41598-025-12367-y.
Peatland cloud forests, characterized by high altitude and humidity, are among the least-studied tropical ecosystems despite their significance for endemism and the bioavailable nitrogen (N) that can be emitted as NO. While research has mainly focused on soil, the above-ground microbial N cycle remains largely unexplored. We quantified microbial N cycling genes across ecosystem compartments (soil, canopy soil, tree stems, and leaves) in relation to NO and N fluxes and soil physicochemical properties in two peatland cloud forests and a wetland on Réunion Island. Complete denitrification minimized NO emissions and increased N fluxes in wetland soils. In cloud forest soils, archaeal nitrification primarily produced nitrate (NO), while low pH potentially slowed denitrification, resulting in minimal NO emissions. Soil N-fixers were more abundant in Erica reunionensis-dominated forests than in mixed forests. Tree stems varied between weak NO sinks and sources, with fluxes unrelated to gene abundances in stems. High prokaryotic and fungal nirK gene abundance in forest canopy soil suggests potential for above-ground denitrification in wet conditions. nosZ-I genes found in forest canopy soil and leaves (E. reunionensis, Alsophila glaucifolia, and Typha domingensis) indicate that plants, including forest canopy, may play a significant role in the reduction of NO.
泥炭地云雾森林以高海拔和高湿度为特征，尽管其对于特有物种以及可能以一氧化氮（NO）形式排放的生物可利用氮具有重要意义，但却是研究最少的热带生态系统之一。虽然研究主要集中在土壤方面，但地上微生物氮循环在很大程度上仍未得到探索。我们在留尼汪岛的两片泥炭地云雾森林和一片湿地中，对跨越生态系统各部分（土壤、冠层土壤、树干和树叶）的微生物氮循环基因进行了定量分析，并将其与一氧化氮和氮通量以及土壤理化性质相关联。在湿地土壤中，完全反硝化作用使一氧化氮排放量降至最低，并增加了氮通量。在云雾森林土壤中，古菌硝化作用主要产生硝酸盐（NO），而低pH值可能会减缓反硝化作用，导致一氧化氮排放量极少。在以留尼汪岛石南（Erica reunionensis）为主的森林中，土壤固氮菌比在混交林中更为丰富。树干在一氧化氮弱汇和源之间变化，其通量与树干中的基因丰度无关。森林冠层土壤中高含量的原核生物和真菌nirK基因表明，在潮湿条件下地上存在反硝化作用的潜力。在森林冠层土壤和树叶（留尼汪岛石南、灰绿桫椤和多米尼加香蒲）中发现的nosZ-I基因表明，包括森林冠层在内的植物可能在一氧化氮的还原过程中发挥重要作用。
