Coupled abiotic-biotic cycling of nitrous oxide in tropical peatlands

Atmospheric nitrous oxide (N2O) is a potent greenhouse gas thought to be mainly derived from microbial metabolism as part of the denitrification pathway. Here, we report that in unexplored peat soils of Central and South America, N2O production can be driven by abiotic reactions (≤ 98 %) highly competitive to their enzymatic counterparts. Extracted soil iron positively correlated with in-situ abiotic N2O production determined by isotopic tracers. Moreover, we found that microbial N2O reduction accompanied abiotic production, essentially closing a coupled abiotic-biotic N2O cycle. Anaerobic N2O consumption occurred ubiquitously (pH 6.4-3.7), with proportions of diverse clade II N2O-reducers increasing with consumption rates. Our findings show denitrification in tropical peat soils is not a purely biological process, but rather a “mosaic” of abiotic and biotic reduction reactions. We predict hydrological and temperature fluctuations differentially affect abiotic and biotic drivers and further contribute to the high N2O flux variation in the region.大气一氧化二氮（N₂O）是一种强效温室气体，此前认为其主要源自作为反硝化途径组成部分的微生物代谢过程。本研究报道，在中美洲和南美洲未被探索过的泥炭土中，一氧化二氮的产生可由非生物反应驱动，其贡献占比最高可达98%，与对应的酶促反应极具竞争力。提取得到的土壤铁与通过同位素示踪剂测定的原位非生物一氧化二氮产生量呈显著正相关。此外，我们发现微生物一氧化二氮还原与非生物产生过程相伴发生，实质上形成了一个耦合的非生物-生物一氧化二氮循环。厌氧一氧化二氮消耗现象普遍存在（pH范围3.7~6.4），且多样的II类一氧化二氮还原菌（clade II N₂O-reducers）的相对丰度随消耗速率升高而增加。我们的研究结果表明，热带泥炭土中的反硝化作用并非纯粹的生物学过程，而是由非生物与生物还原反应共同构成的“镶嵌体”。我们预测，水文与温度波动会对非生物和生物驱动因子产生差异化影响，进而进一步加剧该区域一氧化二氮通量的高变异性。