Optode-based chemical imaging of laboratory burned soil reveals millimeter-scale heterogeneous biogeochemical responses

11 November 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Soil spatial responses to fire are unclear. Using optical chemical sensing with planar ‘optodes’, pH and dissolved O2 concentration were tracked spatially with a resolution of 360 µm per pixel for 72 hours after burning soil in the laboratory with a butane torch (~ 1300 °C) and then sprinkling water to simulate a postfire moisture event. Imaging data from planar optodes correlated with microbial activity (quantified via RNA transcripts). Post-fire and post-wetting, soil pH increased throughout the entire ~ 13 cm × 17 cm × 20 cm rectangular cuboid of sandy loam soil. Dissolved O2 concentrations were not impacted until the application of water postfire. pH and dissolved O2 both negatively correlated (p < 0.05) with relative transcript expression for galactose metabolism, the degradation of aromatic compounds, sulfur metabolism, and narH. Additionally, dissolved O2 negatively correlated (p < 0.05) with carbon fixation pathways in Bacteria and Archaea, amoA/amoB, narG, nirK, and nosZ. nifH was not detected in any samples. Only amoB and amoC correlated with depth in soil (p < 0.05). Results demonstrate that postfire soils are spatially complex on a mm scale and that using optode-based chemical imaging as a chemical navigator for RNA transcript sampling is effective.


optical sensing
microbial ecology

Supplementary materials

SUPPORTING INFORMATION FOR: Optode-based chemical imaging of laboratory burned soil reveals millimeter-scale heterogeneous biogeochemical responses
Supporting Methods describing the fabrication and calibration procedures for the optical chemical sensors (optodes) and additional data to support the main text as well as a table showing the ion characterisation of the soil.
Videos of the pH optode and the O2 optode
The videos show the spatiotemporal change in pH values of the soil post-burn as well as the spatiotemporal change in O2 concentration within the same soil post-burn.


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