Abstract

Redox fluctuations can alter the pools of reducible Fe^III and mineralizable C, and shift the activity and composition of the microbial community that drive these biogeochemical cycles. We hypothesized that in redox fluctuating soils, the rates of Fe reduction and C mineralization during anoxic conditions (τ_anoxic) will respond to the length of time the system was exposed to the previous oxic conditions (τ_oxic). To test this hypothesis, we exposed a soil from the upper 15 cm of the Luquillo Critical Zone Observatory (CZO), Puerto Rico, to five redox fluctuation scenarios. A Long τ_anoxic of 6 d with τ_oxic of 8, 24, and 72 h (L-8, L-24, and L-72), or a Short τ_anoxic of 2 d with τ_oxic of 8 or 24 h (S-8 and S-24). For the long oscillation periods, we found that a decrease from 72 to 24 to 8 h in the preceding τ_oxic impacted the subsequent τ_anoxic as follows: Fe reduction rates increased, CH₄ emissions decreased, and CO₂ fluxes did not change. For the short oscillation treatments (S-8 and S-24), under τ_anoxic, rates of Fe reduction, CO₂ and CH₄ emissions all decreased throughout the experiment. Our results demonstrate that in redox dynamic environments, the length of time a soil is exposed to oxygen can impact the rates of iron reduction and methanogenesis in the subsequent anoxic intervals. Predictions of anaerobic processes (e.g., CH4 production) must take this environmental memory effect of oxygen exposure into account when estimating the influence of anaerobic processes on greenhouse gas emissions.

Citation

Barcellos, Diego, Ashley Campbell, Jennifer Pett-Ridge, Aaron Thompson (2019): Length of Oxygen Exposure during Redox Oscillations Affects Rates of Iron Reduction, Anaerobic Carbon Mineralization, and Methane Emissions. Soil Science Society of America International Soils Meeting, San Diego, CA, 6-9 January 2019.

This Paper/Book acknowledges NSF CZO grant support.