Dynamic Associations Between Ammonia-Oxidizing Archaea and Plants Drive Soil Nitrogen and Carbon Cycling

One of the momentous undertakings of our time is our exploration of the incredible and long hidden world of microorganisms intricately involved in all matters of life and death. In light of increasingly extreme weather events and extensive environmental degradation, a promising domain of particular interest is that of Archaea, which holds unique and exciting adaptive capabilities and significantly influences ecosystems and economies across the globe via biogeochemical cycling. Specifically, ammonia-oxidizing archaea (AOA) are a group that help carry out the rate-limiting step of an essential component of the global nitrogen (N) cycle: nitrification. Concerningly, nitrification combined with nitrate leaching in recent years has led to considerable soil fertility losses and the eutrophication of waterways. While recent studies have identified a few possible biological and synthetic inhibitors of nitrification, the mechanisms of such inhibition, and its impacts on plant growth, are not well understood. Growing soil AOA Nitrososphaera viennensis in controlled, fabricated ecosystems, we interrogated archaeal nutrient and signaling dynamics in the presence of the biofuels feedstock switchgrass (Panicum virgatum). Using biochemistry, metabolomics, and transcriptomics, we characterized the molecular interplay between plants, archaea, and their surrounding environment. We found that plant age and root exudate profiles corresponded with shifts in the nitrification activity of AOA. In addition, the presence of AOA correlated with increases in plant height, weight, and total carbon (C) levels. We confirmed both stimulatory and inhibitory impacts of various plant exudate metabolites on AOA with follow-up experimentation. This work improves our mechanistic understandings of the microbial controls in soil N and C cycling and plant-microbe interactions, as well as informs future efforts to improve nutrient use efficiency, increase carbon capture, and engineer host microbiomes for growth.