SPATIAL AND TEMPORAL MAPPING OF DISSOLVED ORGANIC MATTER TRANSFORMATIONS IN THE RHIZOSPHERE USING SUBSURFACE GAS AND AQUEOUS PHASE PROBE NETWORKS

The biological, chemical and physical properties of soil immediately surrounding roots differ substantially from bulk soil and play a critical role in globally significant ecological processes including soil formation, nitrogen cycling and carbon cycling. Despite its small spatial extent, this root zone (the rhizosphere) is responsible for a disproportionately large percentage of transformations of chemical species that control soil organic carbon accrual and loss. The overall objective of this project is to explore the complex interactions between roots, microbial communities, and organic matter in the rhizosphere under natural conditions using a novel integrated measurement system that quantifies dissolved species, soil gases, and their transformations with high spatial and temporal resolution. An automated, non-destructive, in-situ, soil liquid sampling system with high spatial (millimeter), temporal (minute) and molecular resolution will be developed to observe low molecular weight dissolved organic matter transformations at previously inaccessible spatiotemporal scales. Arrays of these microdialysis-based probes will be combined with existing gas probes and with metagenomic/metatranscriptomic microbial characterization to inform and challenge rhizosphere reactive transport models.This project will be divided into three phases and experimental goals:1) Characterize the impact of root exudation on dissolved organic matter transformations and transport by combining reactive transport models with results from well-constrained experiments centered on an artificial root:a) Use exudate dosing (sugar, amino acid, organic acid, mixture) toobserve transport of exudate and dissolved organic matter (DOM) transformations including trace gas products and microbial responseb)Homogeneous 13C/ 15N low molecular weight (LMW) DOM dosingwith model root to understand the fate of these species2) Utilize the same probe technology and modeling approach to evaluate a living root in different growth stages to observe the establishment and evolution of the rhizosphere in situ, and quantify rhizosphere responses to environmental stressors.a) Probe the rhizosphere of a real root growing in natural conditions to undertsand real-world exudate composition and gradientsb) Explore these interactions under different plant stressors.3) Scale up to a greenhouse setting where we will investigate the impacts of symbiotic relationships on carbon and nitrogen resource utilization in the rhizosphere.a) Understand the role of mychhorizal interaction in modulating and mediating LMW DOM in the rhizosphere.In addition to these technical goals, we aim to introduce high school, undergraduate, and graduate students to world-class research environments in academic and industrial settings. We will achieve this through collaborations with U. of Arizona and Penn. State are, whose undergraduate and graduate students will participate. In addition, we will utilize local high school interns for laboratory work in the summer, including developing "mini-projects" (e.g. measuring soluble carbon and nitrogen) that are matched to their skill levels.