Page 222 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 9. Long-term warming effects on permafrost soil microbial communities
fractions are solely available in the long run. These conditions are specifically relevant to feed climate models with the boundary response potential of microbial communities. However, our set-up excluded the contact to meltwater fluxes that carry gases and nutrients in field conditions.
The three layers exhibited a general trend with an adaptation to the depletion of labile carbon and alternative terminal acceptors within approximately one year, despite of the heterogeneity of the initial geochemistry of the three layers, and the significantly different CH4 production potentials that were observed. This closed-off incubation system, minimizes biases induced by other factors, including e.g. temperature, water table, and availability of nutrients. The system has imposed strong stress on the microbial population to favor lineages which can survive and function under alternative electron acceptor and labile carbon depleted conditions. The three different layers showed that permafrost thaw can lead to both taxonomic and functional adaptations for metabolizing less labile carbon on the long-term, which is unlikely to be caused by stochastic processes alone. This long-term microbial mechanism allows for relatively stable, but low GHG production on the long-term compared to short-term scenarios. Our data provides an important concept for the long-term permafrost feedback loop in a warming world (Fig. 8).
Figure 8. Conceptualized illustration on short- and long-term effects on greenhouse gas production and community adaptations following permafrost thaw and anoxic incubation at above-zero temperatures of permafrost-affected soils. The background color denotes the short-term and long-term incubation in purple and yellow, respectively. Arrows indicate positive effects, while stop line indicate negative effects. The figure shows that GHG production in permafrost-affected soils can be directly modulated through microbial taxonomic and functional shifts. This concept is based on data from Mackelprang et al. (2011) (short-term responses) and this study (long-term responses).

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