Impact of redox fluctuations on the spatial distribution of the microbial community in a forest soil: A lysimeter experiment

The soil microbial community is structured by several factors including environmental conditions such as varying water content, dissolved oxygen, and redox potential. Here, we experimentally investigate the impact of the redox regimes, i.e., oxic, fluctuating, or anoxic conditions, on the microbial community composition and probe the widespread hypothesis that the diversity of the redox fluctuating layer is greater than that of the zones with static redox conditions. A 50-cm homogenized soil column was subjected to realistic intermittent artificial precipitation for 3 months and the hydrological and geochemical parameters (redox potential, pH, dissolved oxygen, soil moisture, matric potential, chemical speciation) measured as a function of time and depth. The change in microbial community over the 3-month experiment was distinct in the three redox zones. The oxic zone exhibited increased biomass and the highest diversity, the redox fluctuation zone exhibited less growth and diversity, and the anoxic zone was characterized by little change in biomass and minimal change in diversity. Interestingly, the redox fluctuation zone and anoxic zone microbiomes most resembled that of the initial soil. Rather than the redox potential alone, the vertical DOC gradients were found to dominate the compositional trajectory of the microbiome. Additionally, this work validated a recently developed spatially explicit biogeochemical model with both geochemical and microbial data and revealed the horizontal and vertical characteristics of microbial community diversity under varying hydrological regimes. ### Competing Interest Statement The authors have declared no competing interest.