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

Hubert Jochheim,Horst H Gerke,Christoph Haas,Sinikka Paulus,Martin Maier,Stephan Wirth

doi:10.5194/egusphere-egu2020-17686

Abstract

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;To investigate CO&lt;sub&gt;2&lt;/sub&gt; 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&amp;#8217;s law to vertical profiles of soil CO&lt;sub&gt;2&lt;/sub&gt;. The FGA uses the soil gas diffusivity to calculate vertical fluxes of soil CO&lt;sub&gt;2&lt;/sub&gt; and the CO&lt;sub&gt;2&lt;/sub&gt; efflux from soil. The vertical partitioning the production of CO&lt;sub&gt;2&lt;/sub&gt; in different soil layers can be regarded as an option and an advantage of FGA as compared to chamber methods.&lt;/p&gt;&lt;p&gt;This investigation aims at clarifying whether a spline or an exponential function is more suitable for fitting vertical distributions of measured CO&lt;sub&gt;2&lt;/sub&gt; concentrations. We compared simulation results on the CO&lt;sub&gt;2&lt;/sub&gt; efflux and the vertical distribution of CO&lt;sub&gt;2&lt;/sub&gt; production within the soil when applying an exponential function or a spline function, respectively. Soil CO&lt;sub&gt;2 &lt;/sub&gt;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 CO&lt;sub&gt;2&lt;/sub&gt; efflux was estimated by applying the manual chamber method. The results suggest that vertical distribution function of soil CO&lt;sub&gt;2&lt;/sub&gt; affects both the calculated CO&lt;sub&gt;2&lt;/sub&gt; efflux and the production of soil CO&lt;sub&gt;2&lt;/sub&gt;. The CO&lt;sub&gt;2&lt;/sub&gt; efflux from the chamber method fits best with the CO&lt;sub&gt;2&lt;/sub&gt; efflux from spline function. We discus some effects with the application of the spline function on the calculated vertical distribution of CO&lt;sub&gt;2&lt;/sub&gt; production.&lt;/p&gt;

Full Text