Controlled redox potentials and flooding duration affect microbial community composition and biomass in an arable soil

Redox conditions regulate biogeochemical cycling and microbial communities in soils. However, the extent to which redox potentials (E_H) affect microbial community composition remains unclear. This study elucidates the effects of controlled E_H on microbial biomass and on bacterial, fungal, and archaeal abundance.

An arable soil with stagnant properties was flooded and incubated under stable E_H at 100, 300, 400, and 550 mV (standardized to pH 7). Microbial community composition was investigated by phospholipid fatty acid (PLFA) analysis and quantitative polymerase chain reaction (qPCR) targeting 16S and 18S rRNA genes. Additionally, relevant electron acceptors (NO₃⁻, Mn, Fe, SO₄²⁻), organic carbon (C), nitrogen, and nutrients (P and S) were measured in the dissolved phase to link anaerobic respiration and nutrient availability with microbial community composition.

Microbial biomass and community composition were affected by E_H and flooding duration. Bacterial, fungal, and archaeal gene copy numbers were lowest at 100 mV and decreased with flooding duration. The microbial community composition differed between reducing and oxidizing redox conditions, especially between 100 and 400 mV. This change was associated with nitrification at ≥ 400 mV and lower energy net yields at 100 mV due to microbial Mn reduction compared to NO₃⁻ reduction or aerobic respiration. Electron acceptor and nutrient availability explained over 50 % of variation in microbial community composition.

We conclude that E_H and flood duration regulate microbial biomass, community composition, and respiration pathways in flooded soils primarily through their effects on electron acceptor and nutrient availability.