SHIFTS OF SOIL MICROBIAL COMMUNITIES IN ALASKAN TUNDRA IN RESPONSE TO LONG-TERM WARMING

Abstract

Permafrost regions store about 33% of the world’s soil organic carbon, and are believed to rapidly respond to global warming. The degradation and release of previously stored organic carbon stocks lead to positive feedbacks, potentially further accelerating climate warming. Microorganisms play a crucial role in determining carbon loss in permafrost ecosystems, yet this process is poorly understood. We studied soil microbial community shifts after 5-year experimental warming at the Carbon in Permafrost Experimental Heating Research site (AK, USA) using sequencing of 16S rRNA gene amplicons, and a comprehensive functional gene array (GeoChip 5.0). 16S rRNA analysis showed that the composition and structure of microbial community were significantly changed in response to warming. GeoChip analysis revealed that genes involved in carbon (C) and nitrogen (N) cycling (e.g., C degradation, methane production, N fixation and denitrification) were stimulated under warming. In particular, the significant stimulation of methanogenesis genes suggested that methane release could increase under warming. In addition, both Mantel test and canonical correspondence analysis showed that these changes in diversity and function could be largely explained by thaw depth, plant growth, temperature and moisture. Null model analysis and phylogenetic-based β-nearest taxon index (βNTI) revealed that warming increased the proportion of deterministic processes (i.e., variable selection), indicating that soil microbial communities would be more governed by heterogeneous environmental conditions in a warmer world. Molecular ecological network analysis showed that the network from warmed sites had more complex structure and tighter interactions around environmental factors compared to its counterpart from ambient sites. Together, this study showed both functional potential and composition of soil microbial communities shifted in response to warming, which was highly related to environmental heterogeneity caused by warming.