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The Holocene Epoch (11,700 years ago to the present) marks the development of the present-day boreal ecosystems in interior Alaska. The composition and genetics of soil microbes have the potential to alter how nutrient cycling and vegetation respond to warming and cooling events, but very little is known about how boreal soils have varied over time. Here, we use DNA sequencing on both modern soils and well-preserved paleosols developed during several episodes of the Holocene to extract information on soil bacteria, archaea, and fungi present in interior Alaska during the past 8000 years (8 ka). Community composition of bacteria and fungi in the ancient paleosols was different from modern soils, with a higher relative abundance of Proteobacteria, Chloroflexi, and Verrucomicrobia in the modern soils. The most dramatic shift in interior Alaska's soil microbiome occurred ca. 7 ka, when species diversity was lowered and functional diversity became higher after 7 ka. This suggests that function was truly low, the early Holocene ecosystems were functionally redundant, and/or that true functional diversity was not captured due to a lack of genetic resolution in existing sequence databases. The cause of this observed shift cannot be directly answered in this work; however, these data suggest that ca. 7 ka was a critical period when microbial taxa and function shifted dramatically. This is important for understanding how the soil microbiome responds to climate changes and impacts the succession of vegetation. [ABSTRACT FROM AUTHOR]

The middle Tanana Valley of central Alaska contains a well‐preserved record of human occupation and paleoenvironmental change since the Late Glacial period (c. 16,000 cal yr BP) and is a critical region for understanding human dispersal into the Americas. Micromorphology analysis of soils and sediments from six archaeological sites yields valuable information about soil formation processes and landscape evolution during the Late Glacial and into the Holocene. At the macroscale, site stratigraphies are very similar, and thin organic‐rich layers (locally known as "stringers") are commonly interpreted as buried soils. However, at the microscale, these layers exhibit significant differences in the degree of bioturbation, organic matter humification, and boundary abruptness, indicating that pedogenesis was not the sole process at every site. In this way, our microscale analysis addresses issues of equifinality related to site formation interpretations, a persistent problem with subarctic and high‐latitude stratigraphy. Additionally, this study reveals a certain level of landform and landscape instability within a broader trend of regional increases in pedogenesis and vegetation coverage, adding to the existing model of heterogeneity across this subarctic landscape. Here we demonstrate the utility of micromorphology to test field interpretations and improve models of Late Glacial landscape evolution in high‐latitude contexts. [ABSTRACT FROM AUTHOR]