Inorganic carbon fluxes across the vadose zone of planted and unplanted soil mesocosms

[摘要] The efflux of carbon dioxide (CO₂) from soils influences atmosphericCO₂ concentrations and thereby climate change. The partitioning ofinorganic carbon (C) fluxes in the vadose zone between emission tothe atmosphere and to the groundwater was investigated to reveal controllingunderlying mechanisms. Carbon dioxide partial pressure in the soil gas(pCO₂), alkalinity, soil moisture and temperature were measured overdepth and time in unplanted and planted (barley) mesocosms. The dissolvedinorganic carbon (DIC) percolation flux was calculated from the pCO₂,alkalinity and the water flux at the mesocosm bottom. Carbon dioxideexchange between the soil surface and the atmosphere was measured at regularintervals. The soil diffusivity was determined from soil radon-222(²²²Rn) emanation rates and soil air Rn concentration profiles and wasused in conjunction with measured pCO₂ gradients to calculate the soilCO₂ production. Carbon dioxide fluxes were modeled using the HP1module of the Hydrus 1-D software.

The average CO₂ effluxes to the atmosphere from unplanted and plantedmesocosm ecosystems during 78 days of experiment were 0.1 ± 0.07 and4.9 ± 0.07 μmol C m⁻² s⁻¹, respectively, and grosslyexceeded the corresponding DIC percolation fluxes of 0.01 ± 0.004 and0.06 ± 0.03 μmol C m⁻² s⁻¹. Plant biomass was highin the mesocosms as compared to a standard field situation. Post-harvestsoil respiration (R_s) was only 10% of the R_s during plantgrowth, while the post-harvest DIC percolation flux was more than one-thirdof the flux during growth. The R_s was controlled by production anddiffusivity of CO₂ in the soil. The DIC percolation flux was largelycontrolled by the pCO₂ and the drainage flux due to low solution pH.Modeling suggested that increasing soil alkalinity during plant growth wasdue to nutrient buffering during root nitrate uptake.

[学科分类] 地球化学与岩石