The effect of vertical distribution functions on CO2 efflux and production calculated with the flux gradient approach

Soil respiration is one of the most significant carbon fluxes in terrestrial ecosystems. The analyses and quantification of soil CO2 production and its influencing factors play a crucial role in the understanding of the global carbon budget.

To investigate CO₂ efflux from terrestrial soils under field conditions, manual or automated soil chambers are the most common methods. The flux-gradient approach (FGA) as an alternative method applies Fick’s law to vertical profiles of soil CO₂. The FGA uses the soil gas diffusivity to calculate vertical fluxes of soil CO₂ and the CO₂ efflux from soil. The vertical partitioning the production of CO₂ in different soil layers can be regarded as an option and an advantage of FGA as compared to chamber methods.

This investigation aims at clarifying whether a spline or an exponential function is more suitable for fitting vertical distributions of measured CO₂ concentrations. We compared simulation results on the CO₂ efflux and the vertical distribution of CO₂ production within the soil when applying an exponential function or a spline function, respectively. Soil CO₂ concentrations were measured at the soil surface and at 0, 0.1, 0.2, 0.3 and 1.0 m soil depth of a Scots pine and a European beech forest stand of the Northeast German Lowlands. Additionally, the CO₂ efflux was estimated by applying the manual chamber method. The results suggest that vertical distribution function of soil CO₂ affects both the calculated CO₂ efflux and the production of soil CO₂. The CO₂ efflux from the chamber method fits best with the CO₂ efflux from spline function. We discus some effects with the application of the spline function on the calculated vertical distribution of CO₂ production.