The Soil Microbiome and Its Response to Permafrost Thaw in Arctic Tundra

• Main Author: Romanowicz, Karl
• Other Authors: Kling, George W, Dick, Gregory James, Denef, Vincent J, Schmidt, Thomas M
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: microbial ecology; Arctic climate change; permafrost thaw; Ecology and Evolutionary Biology; Science; Arctic; Climate change; permafrost; Tundra
• Online Access: https://hdl.handle.net/2027.42/174188; https://doi.org/10.7302/5919

A majority (~60%) of the global belowground organic carbon (OC) pool is trapped in a perennially frozen state in permafrost soils underlying the Arctic tundra. Climate warming has initiated thaw in large regions of permafrost. Such thaw will likely trigger increased microbial activity leading to faster degradation of previously frozen OC and its release as carbon dioxide (CO2) and methane (CH4) to the atmosphere. Yet it remains uncertain how the soil microbiome (community of microorganisms) will respond to permafrost thaw or modulate the relative proportions of CO2 and CH4 produced by the decomposition of OC in thawing permafrost soils. This dissertation advances our understanding of the dynamics and functions of the tundra soil microbiome in response to permafrost thaw using field-based and laboratory experiments. Permafrost soils remain water-saturated during thaw, leading to oxygen (O2) limitations that promote anaerobic and fermentative microbial processes responsible for OC degradation. Rainfall contributes to soil saturation but can also introduce an influx of O2, potentially altering anaerobic metabolism and reducing CH4 production. A rainfall event was simulated in tundra soil mesocosms and the genomic response of the soil microbiome was assessed through a multi-omics sequencing approach. Soil drainage rates had the greatest effect on soil oxygenation following the rainfall event. Specifically, rainfall-induced soil oxidation increased aerobic microbial metabolism and CO2 respiration in a slow-draining tundra soil. However, the residence time of oxygenated rainwater in a rapidly-draining tundra soil was insufficient to alter anaerobic and fermentative microbial processes that continued to promote CH4 production. Thus, the microbial response to rainfall in thawing permafrost soils depends on drainage rates that differ by tundra type. The microbial response to permafrost thaw also depends on how thaw duration (thaw days in summer) affects the composition of the soil microbiome. Field observations revealed ...