Free Iron and Iron-Reducing Microorganisms in Permafrost and Permafrost-Affected Soils of Northeastern Siberia

An agreement between the content of amorphous (oxalate-extractable) iron and morphochromatic features of gley attests to the modern activity of gleyzation processes in tundra soils of the Kolyma Lowland, especially within lower parts of gentle and steep slopes. A suprapermafrost reduced gley horizon thawing out in the warmest years is considered a relic of the warmer and wetter stage of soil formation. An integrated analysis of data on the contents of mobile iron and annotated metagenomes indicates that microorganisms affiliated with the Proteobacteria phylum capable of iron reduction predominate in sediments formed under hydromorphic conditions and in modern mineral soil. In laboratory experiments, the process of microbial iron reduction was more active at 5°C than at 20°C. Therefore, it can be assumed that the majority of cultivated communities of iron-reducing bacteria have been adapted to low Arctic temperatures. Under conditions of climate warming and an increase in precipitation, permafrost temperature, and thickness of the seasonally thawed layer, iron reduction processes in the soils rich in the total iron will play an even greater role and create favorable redox conditions for the formation of methane, one of the most important greenhouse gases.