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Microbial drivers of soil biogeochemistry and carbon flux in recently deglaciated soils
Scott Sugden, Jeremy Bougoure, Dehong Hu, Lye Meng Markillie, Cynthia Kallenbach, Lyle Whyte
As glaciers continue to retreat due to ongoing climate change, they leave behind nutrient-poor foreland soils that are quickly colonized by microbial communities. Although previous studies have characterized the general process of microbial succession in deglaciated soils, few have explored which taxa and metabolisms dominate the biogeochemical fluxes of carbon, nitrogen, and other nutrients, despite the importance of this information for future climate and landscape models. In this study-in-progress, we explored microbial community assembly and biogeochemical activity over approximately 150 years of succession in five polar glacier forelands in the Canadian High Arctic and Antarctic Peninsula. We used metagenomic and metatranscriptomic sequencing, combined with in situ gas flux measurements and an isotope-labeling experiment, to identify the abundant and active nutrient-cycling pathways in soils of different ages and quantify the activity of individual cells. Soils were incubated with 13CO2 and 15N2 for three weeks, with samples collected weekly. The dominant litho- and photoautotrophs were visualized using fluorescence in situ hybridization, and their activity and isotopic enrichment over time were quantified at the single-cell level using nanoscale secondary ion mass spectroscopy. We observed a general trend from litho- to photoautotrophy with soil age, though autotrophic metabolisms still dominate even in >100-year-old soils. We also noted that cellular activity increases with soil age, heterotrophs rely almost exclusively on newly fixed carbon, and older soils become a strong methane sink. Overall, our results demonstrate the pathways and processes that drive soil development in one of the most rapidly changing ecosystems on the planet.
