Matus Francisco, Álvarez Enzo, Godoy Roberto, Iturriaga-Vásquez Patricio, Farías-Cea Amaury, Parada José, Merino Carolina, Nájera Francisco, Mendoza Daniela, Jofré Ignacio, Knicker Heike, Dippold Michaela A, Kuzyakov Yakov, Schluesselburg Lia, Boy Jens
Faculty of Engineering and Sciences, Laboratory of Soil Conservation and Dynamics of Volcanic Soils, Universidad de La Frontera, Temuco, 4780000, Chile.
Faculty of Engineering and Sciences, Laboratory of Soil Conservation and Dynamics of Volcanic Soils, Universidad de La Frontera, Temuco, 4780000, Chile.
J Environ Manage. 2025 Sep;391:126311. doi: 10.1016/j.jenvman.2025.126311. Epub 2025 Jul 2.
Understanding the pathways of nitrogen (N) retention in pristine forest soils is essential for effective ecosystem management and nutrient conservation. The incorporation of nitrate (NO) and nitrite (NO) into organic N in soils without microbiological contribution remains a very intriguing question. This study explores the abiotic incorporation of nitrate (NO) and nitrite (NO) into organic N of volcanic soil under sterilized and anoxic conditions, providing insights into mineral N losses occurring as dissolved organic N (DON) rather than the commonly accepted nitrate leaching. We evaluated the hypothesis that nitrate (NO) can be reduced to nitrite (NO), which subsequently reacts with organic matter through nitration and nitrosation, leading to the formation of organic nitrogen. This mechanism, which is of great ecological significance, supports the Ferrous Wheel Hypothesis (FWH). The FWH proposes that ferrous iron, Fe(II), reduces NO to NO within anaerobic microsites, and that Fe(II) is then re-oxidised to ferric iron, Fe(III), contributing to the formation of dissolved organic N (DON). Both NO and NO declined rapidly by 51 and 94 %, while labelled organic N increased by 20-38 % for NO and 42-44 % for NO within seconds. The incorporation of N into organic forms was confirmed using ATR-FTIR and benzene:isopropanol extraction, with the lowest and highest accumulation observed at 5 and 15 mg NO⁻ kg⁻¹, respectively. These results demonstrate that NO incorporation into organic N can occur primarily through abiotic processes, supporting the FWH, as both DON and solid-phase organic N were measured. These findings highlight the natural resilience of volcanic soils in unpolluted old-growth temperate rainforests to N loss and provide new insights into long-term ecosystem stability and nutrient cycling. Further research should investigate the interplay between abiotic and biotic N transformations under field conditions and across diverse forest ecosystems.
了解原始森林土壤中氮（N）的保留途径对于有效的生态系统管理和养分保护至关重要。在没有微生物作用的情况下，将硝酸盐（NO）和亚硝酸盐（NO）纳入土壤中的有机氮仍然是一个非常有趣的问题。本研究探讨了在无菌和缺氧条件下，硝酸盐（NO）和亚硝酸盐（NO）非生物地纳入火山土壤有机氮的情况，为以溶解有机氮（DON）形式而非普遍认为的硝酸盐淋溶形式发生的矿质氮损失提供了见解。我们评估了这样一个假设，即硝酸盐（NO）可以还原为亚硝酸盐（NO），随后亚硝酸盐通过硝化和亚硝化与有机物反应，导致有机氮的形成。这种具有重要生态意义的机制支持了“Ferrous Wheel Hypothesis”（FWH）。FWH提出，亚铁（Fe(II)）在厌氧微位点内将NO还原为NO，然后Fe(II)再氧化为铁（Fe(III)），这有助于溶解有机氮（DON）的形成。在几秒钟内，NO和NO分别迅速下降了51%和94%，而标记的有机氮对于NO增加了20 - 38%，对于NO增加了42 - 44%。使用衰减全反射傅里叶变换红外光谱（ATR - FTIR）和苯：异丙醇萃取法证实了氮被纳入有机形式，分别在5和15 mg NO⁻ kg⁻¹时观察到最低和最高积累量。这些结果表明，NO纳入有机氮主要可通过非生物过程发生，支持了FWH，因为同时测量了DON和固相有机氮。这些发现突出了未受污染的老龄温带雨林中火山土壤对氮损失的自然恢复力，并为长期生态系统稳定性和养分循环提供了新见解。进一步的研究应调查野外条件下以及不同森林生态系统中非生物和生物氮转化之间的相互作用。
