Positron‐emitting radiotracers spatially resolve unexpected biogeochemical relationships linked with methane oxidation in Arctic soils

• Published in: Global change biology 2022-07, Vol.28 (13), p.4211-4224
• Main Authors: Schmidt, Michael P., Mamet, Steven D., Senger, Curtis, Schebel, Alixandra, Ota, Mitsuaki, Tian, Tony W., Aziz, Umair, Stein, Lisa Y., Regier, Tom, Stanley, Kevin, Peak, Derek, Siciliano, Steven D.
• Format: Article
• Language: English
• Subjects: Arctic soils; Arctic zone; Biogeochemistry; Biological activity; carbon cycling; Climate; Diapirism; Dynamics; Environmental factors; Frost; Furuncles; Gas dynamics; Genes; Global climate; Greenhouse gases; Metabolism; Metagenomics; Methane; methane fluxes; methane oxidation; methanotrophy; Microbial activity; Microorganisms; nitrogen cycling; Nutrients; Organic carbon; Oxidation; Radioactive tracers; radioisotopes; Soil; Soil bacteria; soil biogeochemistry; Soil dynamics; Soils; Speciation; Uptake
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.16188

Arctic soils are marked by cryoturbic features, which impact soil‐atmosphere methane (CH4) dynamics vital to global climate regulation. Cryoturbic diapirism alters C/N chemistry within frost boils by introducing soluble organic carbon and nutrients, potentially influencing microbial CH4 oxidation. CH4 oxidation in soils, however, requires a spatio‐temporal convergence of ecological factors to occur. Spatial delineation of microbial activity with respect to these key microbial and biogeochemical factors at relevant scales is experimentally challenging in inherently complex and heterogeneous natural soil matrices. This work aims to overcome this barrier by spatially linking microbial CH4 oxidation with C/N chemistry and metagenomic characteristics. This is achieved by using positron‐emitting radiotracers to visualize millimeter‐scale active CH4 uptake areas in Arctic soils with and without diapirism. X‐ray absorption spectroscopic speciation of active and inactive areas shows CH4 uptake spatially associates with greater proportions of inorganic N in diapiric frost boils. Metagenomic analyses reveal Ralstonia pickettii associates with CH4 uptake across soils along with pertinent CH4 and inorganic N metabolism associated genes. This study highlights the critical relationship between CH4 and N cycles in Arctic soils, with potential implications for better understanding future climate. Furthermore, our experimental framework presents a novel, widely applicable strategy for unraveling ecological relationships underlying greenhouse gas dynamics under global change. Soil microbial greenhouse gas exchange processes require suitable biogeochemical conditions and microbial communities to occur. Spatial heterogeneity within complex soil matrices makes studying these conditions difficult. We use 11C‐labelled methane to visualize small‐scale microbial methane uptake in cryodisturbed Arctic desert soils to address these challenges. We find that methane uptake spatially associates with distinct nitrogen speciation and microbial communities not previously related to methane uptake. The novel radiotracer‐based approach established here provides new insights into methane cycling in Arctic soils but is widely applicable to studying greenhouse gas dynamics in soils.