The role of root-soil interactions in shaping greenhouse gas dynamics from thawing permafrost soils

• Applicants: Professor Dr. Andreas Kappler; Professorin E. Marie Muehe, Ph.D.
• Subject Area: Soil Sciences ; Microbial Ecology and Applied Microbiology ; Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465839667

About one-third of all soil surface carbon on Earth is locked up in permafrost soils. Thawing permafrost soils have been identified as a significant source of the greenhouse gases carbon dioxide, methane, and nitrous oxide. Carbon dioxide is the product of overall biota respiration, with plants and photosynthesizing microbes counterbalancing production in photosynthesis. More of a problem are methane and nitrous oxide with respective global warming contributions of 28 and 265 times that of carbon dioxide. By the end of this century, Arctic permafrost peatlands are predicted to warm from below 2°C to annually averaged 5.6 to 12.4°C, resulting in significant permafrost thaw and subsequent mobilization of organic carbon and nitrogen. Thus, microbial turnover of newly mobilized organic material will reflect an unpredictable amount of produced greenhouse gases. The microbial production of greenhouse gases in permafrost peatlands is only one aspect of the story though. The subsequent release of the produced greenhouse gases from soil into the atmosphere is also crucial to consider. Permafrost tundras are successfully colonized by a variety of plants whose roots grow through the soil during seasonal thaw. The sheer physical impact of growing roots with diverse morphological traits including air trapping in root-adjacent air pockets, and their myriad ways of interplay with the abiotic and microbial soil environment in the rhizosphere alter multiple biogeochemical and physical soil processes. Further, the release of organic carbon as root exudates may fuel microbial processes producing greenhouse gases. Radial oxygen loss from roots inhabiting flooded soils result in the formation of iron mineral coatings around the roots. Such iron plaques are highly reactive interfaces between roots and soil and host a continuum of ecological niches for microbial communities capable of affecting greenhouse gas cycling. What role the root-soil system plays for production, consumption, transport, and release of greenhouse gases from permafrost tundras is subject of this proposal. We will illuminate unique differences in root architecture, organic carbon exudation and iron plaque formation of graminoid and shrub plants that cause an altered microbial community structure responsible for greenhouse gas cycling in permafrost soils. To do so, we will link field studies with laboratory experiments. Rhizospheres of graminoids and shrubs will be monitored visually throughout an entire thaw season using rhizosphere windows placed along a permafrost thaw gradient. Microbial community composition, activity and function will be investigated as a function of root architecture, type of excreted organic carbon and iron plaque formation, and linked to localized greenhouse gas cycling and bulk greenhouse gas emission. Overall, the use of the root-soil system to reduce/control the emission of greenhouse gases from permafrost soils will be investigated in this proposal.

• DFG Programme: Research Grants