| Popis: |
O2 availability is one of the main factors influencing microbial processing of soil carbon and nitrogen and their cycling, and soil pore structure is what drives micro-scale patterns of O2 availability. The diffusivity of O2 is known to be a function of soil porosity and moisture content. However, the actual distribution of O2 in the soil is a product of dynamic interactions between physical (O2 diffusion) and microbial (O2 consumption) processes and is influenced by the soil pore structure. Measurements of gas diffusivity can be achieved via several laboratory techniques, while the determination of O2 consumption by microorganisms is challenging. The objectives of this study are, first, to propose a method for measurement of microbial O2 consumption under steady-state conditions in saturated soil and near saturated soil, and, second, to quantify the rate of O2 consumption in soil materials with contrasting pore structures but similar microbial compositions. The proposed method is based on Fick’s second law of diffusion, given as , where R(z) is an O2 consumption term, C is the concentration of O2, and Ds is the effective molecular diffusion coefficient of O2. The equation was solved for R(z) under steady-state conditions (near saturated soil) where the flux (J)=0. Two soil materials with contrasting pore structures, namely dominated by > 30 μm Ø pores (i.e., large-pore soil) and by < 10 μm Ø pores (i.e., small-pore soil), were prepared. The O2 profile was measured to the depth of 1 cm in the two materials under saturated and near-saturated conditions using O2 microsensor (Unisense, Aarhus, Denmark). As expected, the O2 diffusion was higher in large-pore soil as compared to the small-pore soil, however, the estimated rate of volumetric O2 consumption was also higher in the large-pore soil as compared to the small-pore soil. This finding supports the notion that large pores provide a better micro-environment for soil microorganisms stimulating their activity with subsequent increases in O2 consumption. Our ongoing work builds on these findings and explores the rate and spatial distribution patterns of O2 diffusion and microbial O2 consumption in soils with contrasting pore structures in the presence of plant residues. |
