Novel isotope sensor for spatially-resolved analysis of nutrient exchange in the rhizosphere Topic: 22.a. Technologies for Characterizing the Rhizosphere: Plant-Microbe-Mineral Interactions

Ensuring adequate agricultural productivity in the face of an increasing human population is a major concern with implications for both production of bioenergy products (Jones and Hinsinger, 2008) and global food security. Increasing agricultural productivity requires a stronger understanding of soil biogeochemical processes that impact plant nutrient availability. We propose development of an innovative isotope sensor that will enable high spatial-resolution analysis (down to the microbe level) to target nutrient exchange in the rhizosphere. The concept uses laser ablation to sample specific locations in the roots and rhizosphere at the micron (µm) scale. The resulting, sample- derived ablation particulates are converted to a gas and then analyzed for isotopic content. Specifically, we propose using a novel, ultra-low volume isotope analyzer based on laser absorption spectroscopy, which will initially be used to analyze stable carbon isotope ratios (13C/12C) at high spatial resolution. The resulting tool will enable studies designed to track uptake of isotope labeled 13CO2 from fixation into the plant and eventually through the roots and into the soil as root exudates. The concept builds on successful work in which laser ablation has been coupled to isotope ratio mass spectrometers (IRMS). The innovative aspect is that the IRMS will be replaced by a novel, more sensitive laser absorption spectrometer, which can analyze orders of magnitude smaller sample sizes, enabling smaller ablation spot sizes and improved spatial resolution. Furthermore, as compared to IRMS (as well as other isotope analyzers), our laser absorption spectrometer is more compact, lower power, and more amenable to potential field deployment.