Microbial respiration and its consequences on oxygen availability in peat substrate

Abstract : Oxygen availability to the root not only depends on the gas movement but also on the source-sink relationships involving roots and microorganisms respiration. For some organic soils or substrates, microbial respiration may be very high and could probably make oxygen no more available for the plant. In this context, the main purpose of this study was to model the influence of oxygen consumption by microorganisms in an organic growing media (Sphagnum peat) on oxygen transport and availability to the root. This is why, a one-dimensional transfer coupled model of water and oxygen in porous media was developed taking into account oxygen consumption in the substrate by microorganisms. Simulation results underlined that microbial respiration could cause important reductions in the root oxygen uptake during a one-day time scale simulation (800 mn). For a high microbial respiration rate equal to 120 mg of O2/m3/s, the reduction in oxygen root uptake reaches 60% for the peat substrate. These rapid and important decreases of oxygen content lead to important and sustained anoxic conditions in the root environment.