Intra-aggregate CO2 enrichment: a modelling approach for aerobic soils

[摘要] CO₂ concentration gradients inside soil aggregates, caused by therespiration of soil microorganisms and fungal hyphae, might lead tovariations in the soil solution chemistry on a mm-scale, and to anunderestimation of the CO₂ storage. But, up to now, there seems to be nofeasible method for measuring CO₂ inside natural aggregates withsufficient spatial resolution. We combined a one-dimensional model for gasdiffusion in the inter-aggregate pore space with a cylinder diffusion model,simulating the consumption/production and diffusion of O₂ and CO₂inside soil aggregates with air- and water-filled pores. Our model predictsthat for aerobic respiration (respiratory quotient = 1) the intra-aggregateincrease in the CO₂ partial pressure can never be higher than 0.9 kPafor siliceous, and 0.1 kPa for calcaric aggregates, independent of the levelof water-saturation. This suggests that only for siliceous aggregatesCO₂ produced by aerobic respiration might cause a high small-scalespatial variability in the soil solution chemistry. In calcaric aggregates,however, the contribution of carbonate species to the CO₂ transportshould lead to secondary carbonates on the aggregate surfaces. As regards thetotal CO₂ storage in aerobic soils, both siliceous and calcaric, theeffect of intra-aggregate CO₂ gradients seems to be negligible. Toassess the effect of anaerobic respiration on the intra-aggregate CO₂gradients, the development of a device for measuring CO₂ on a mm-scalein soils is indispensable.

[学科分类] 地球化学与岩石