ABSTRACT

Cryoconite granules are naturally occurring microbial structures on glacier surfaces worldwide. They play a key role in carbon and nitrogen cycling in glacier ecosystems and can accelerate the melting of snow and ice. However, detailed mechanism of nitrogen cycling in cryoconite granules remains unclear. Here, we demonstrate that redox stratification affects the spatial distribution of N cycling processes in cryoconite granules. Based on microsensor measurements for O₂, NH₄⁺, NO₂^– and NO₃^–, we identified the presence of fine-scale redox stratification within cryoconite granules. Cyanobacteria at the surface layer of the granules created oxic conditions, whereas the inner core of the granules was anoxic. Metatranscriptomic analyses indicated the active occurrences of nitrification in the inner core, whereas denitrification actively occurred both in the inner core and the surface layer of the granules. Cyanobacteria in the inner core of the granules were inactive, and likely dead and being degraded, providing carbon and nitrogen to support nitrifiers and denitrifiers. Quantities of nitrification genes/transcripts were greater in large cryoconite granules than small ones, most likely because nitrogen substrates were more abundantly present in the inner core of large granules due to distinct redox stratification. Our results suggest that the development of a granular structure of cryoconite granules can largely affect carbon and nitrogen cycling on glaciers.

中文翻译：

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冰晶石颗粒内的氧化还原分层影响冰川的氮循环

摘要

低温岩颗粒是全世界冰川表面上天然存在的微生物结构。它们在冰川生态系统中的碳和氮循环中起关键作用，并可以加速雪和冰的融化。但是，氮在冰晶石颗粒中循环的详细机制仍不清楚。在这里，我们证明了氧化还原分层会影响冰晶岩颗粒中N循环过程的空间分布。基于微传感器测量代表O ₂，NH ₄ ⁺，NO ₂ ^-和NO ₃ ^- ，我们确定精细尺度氧化还原分层于冰尘颗粒中的存在。蓝细菌在颗粒的表层形成缺氧条件，而颗粒的内核是缺氧的。转录组分析表明内在硝化作用活跃发生，而反硝化作用则在内核和颗粒表层活跃发生。蓝细菌颗粒内核中的碳原子处于非活性状态，很可能死亡并被降解，从而提供了碳和氮来支持硝化器和反硝化器。大尺寸冰晶石颗粒中硝化基因/转录物的数量要多于小颗粒，这很可能是因为氮颗粒由于明显的氧化还原分层而存在于大颗粒的内核中。我们的结果表明，冰晶岩颗粒结构的形成会极大地影响冰川上的碳和氮循环。