Soil microbiomes modulate distinct patterns of soil respiration and methane oxidation in arctic active layer and permafrost

Abstract:

[Objective] This study was aimed to study the difference in respiration, bacterial diversity and community composition of permafrost layer and active layer, and methane consumption potential, and to find the active methylotrophs in soil that has high methane consumption potential. [Methods] Soils were sampled from Adventdalen (Svalbard), Ny-Alesund (Svalbard), Kurungnakh Third terrace (Lena delta) and Lena delta First terrace (Lena delta), including active layers and their corresponding permafrost layers, coming from one intact core at each site in 2013 and they were incubated at 10 ℃ in darkness for 26 days, with or without isotope 13-C labeled methane. Miseq sequencing and quantitative PCR of 16S ribosomal RNA gene and particulate methane monooxygenase pmoA gene were performed to assess difference of bacterial abundance, bacterial diversity and community composition of permafrost layer and active layer. Stable isotope probing experiment with 13-C labeled methane as carbon source was performed to reveal the active methanotrophs in geographically distinct arctic soils. [Results] Active layer soil had higher respiration rate than its permafrost soil, which was positively correlated with the difference of bacterial communities. The respiration rate of active layer ranged from 61 to 623 nmol CO₂/(g dws·d), while exceptionally high respiration rate of 7293/(g dws·d) was observed in LF active layer, and the respiration rate of permafrost layer varied from 47 to 523 nmol CO₂/(g dws·d). The average respiration of Lena delta was 17 times higher than that of Svalbard. Accordingly, active layer had higher bacterial diversity and higher abundance than permafrost soil where the relative abundance of 10 families in active layer were significantly higher than its permafrost. These bacterial families were mainly affiliated with Proteobacteria and Acidobacteria, such as Hyphomicrobiaceae, Solibacteraceae, Sinobacteraceae and their relative abundance was between from 4.3% to 18.6%, 2.6 and 23.7 times higher than that in permafrost layer soil. In Lena delta First terrace active layer with extremely high respiration rate, 6 families (mainly Bacteroidales and Gracilibacteraceae) were found with significant higher relative abundance (26.9%) than in other soils. Only active layer soil from Kurungnakh was observed to have strong methane oxidation potential. The methane oxidation rate in Kurungnakh active layer soil was 55.9 nmol CH₄/(g dws·d). And dominant active methylotrophs of Kurungnakh active layer were phylogenetically affiliated with Crenothrix and type I methane oxidizers (Methylobacterium). [Conclusion] The respiration rate of active layer was higher than its permafrost and with high heterogeneity and this could be well explained by difference of bacterial community composition and bacterial abundance in permafrost and active layer. Repeated thawing and refreezing of active layer has developed characteristic community structure that are key drivers for the turnover of the carbon pool, mainly including Hyphomicrobiaceae, Solibacteraceae and Sinobacteraceae. All these results suggest that microbial community structure in permafrost would go through a succession with a direction to that in its active layer, which might play important role in fixed carbon transformation in permafrost. These results provide a mechanistic understanding towards better optimization of soil carbon emission model under global change scenarios.