Page 201 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

dominant processes shaping microbial communities in permafrost resulted from the stability of the permafrost environment, which imposed both dispersal and thermodynamic constraints (Bottos et al. 2018). This suggests pronounced differences in the microbial metabolic potential between active layer and permafrost soils.
Previous studies and meta-omics projects have provided valuable insights into the response of
the microbial community structure, diversity, food web, and ecology to short-term experimental
warming of permafrost. For example, short-term thaw exposure (2-7 days) can cause a change
in gene composition of former permafrost communities to resemble the active layer (Mackelprang et al. 2011). These findings suggest that prolonged exposure to thaw will likely
lead to even stronger shifts in community structures. Comparative studies on active layer versus permafrost microbial communities, are, however scarce (Mackelprang et al. 2011; Taş et al.
2018), and most previous studies focused on either active layer (Steven et al. 2007; Liebner,
Harder and Wagner 2008; Barbier et al. 2012; Frank-Fahle et al. 2014) or permafrost microbial communities (Bischoff et al. 2013; Rivkina et al. 2016; Bottos et al. 2018). It is obvious that integrally studying these layers is important, since the deepening of the active layer results in cryoturbation on the inter-annual scale in the permafrost-active layer transition zone (Ping et
al. 2015). This can serve as a selective pressure on the permafrost microbial communities that
are progressively exposed within the transient layer. The microbial community also has to
adjust to a decrease in carbon availability as less labile carbon fractions are left after easy- 9 degradable fractions are depleted within a few years after permafrost thaw (Elberling et al.
2013). However, the long-term consequences of permafrost thaw to the microbial community composition and potential are not well understood (Jansson and Taş 2014; Mackelprang et al. 2016).
Understanding the microbial dynamics upon permafrost soil thaw and warming beyond time scales of days and weeks is important to improve current predictive climate models for cold environments, and to refine our knowledge of the magnitude and timing of permafrost carbon emissions in a warming world. Incubation experiments are commonly used to inform valuable parameters for process-based modeling of the permafrost carbon feedback. In particular, models expect a robust response under boundary conditions (e.g. Knoblauch et al. 2018). Upon
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