Spatially-Resolved Microbial Activity Probe Using Infrared Measurements of Nitrous Oxide and Methane Isotopes in Soil

Subsurface microbial activity is central to understanding soil nutrient cycling and ensuring sustainable agricultural productivity. The soil microbiome is a primary contributor to the hydrobiogeochemical processes that impact soil, but it is a highly complex system whose properties can vary quickly and over small spatial scales. The current understanding of the populations, dynamics and influences of microbial communities is limited by the temporal and spatial resolution of the analytical methods used to investigate soil biogeochemical processes. There is a need for innovative tools that can provide fast, localized information about subsurface microbial activity, to challenge existing biogeochemical models, and better inform precision agriculture and ecological policy decisions. The concentrations and isotopic signatures of soil gases are effective messengers of the microbial pathways active in the soil. The overall goal of this DOE SBIR proposal is to design and develop cutting-edge trace gas sensors and novel subsurface soil gas probes that can be coupled, enabling real-time mapping of subsurface biological activity. During Phase I a high precision, small-volume infrared spectrometer for simultaneous measurements of nitrous oxide and methane isotopes was designed and demonstrated. Novel prototype sintered Teflon soil probes were developed, and controlled laboratory testing showed that they can quantitatively transfer soil gas to the spectrometer without isotopic fractionation, as well as to other sensitive trace gas sensor platforms. During Phase II the spectrometer technology will be further developed and the soil probe design refined. A hardware and software interface will be designed to couple an array of probes to a single analysis station, and thus achieve the ultimate goal: a field-ready integrated soil gas measurement system. Finally, the proposed system will be field-demonstrated at two locations: an experimental tropical rainforest area and an agricultural research center, where both the ecological and agronomic value of the measurement capabilities will be demonstrated. Commercial Applications and Other Benefits: The proposed soil probe measurement capability is expected to find wide use in applied agronomic research to optimize soil health and refine nutrient models, in basic ecological research to understand the factors that influence microbial populations, and in atmospheric research to understand the impact of soils upon air quality and climate. The ability to couple the probes to a wide range of trace gas sensors provides major commercialization potential.