The influence of soil structure on heterotrophic respiration response to soil water content

Soil respiration causes one of the largest terrestrial carbon fluxes and its accurate prediction is still a matter of on-going research. Understanding the functional link between soil heterotrophic respiration and soil water content is relevant for the estimation of climate change impacts on soil CO₂ emissions. 
In order to quantify the effect of air-drying and sieving with 2 mm meshes on the soil heterotrophic respiration response to water content we incubated intact cores and sieved samples of two loamy and two sandy agricultural topsoils for six levels of effective soil water saturation. We further measured soil textural properties and the soil water retention characteristics of the soils with the aim to identify potential correlations between soil physical parameters and moisture sensitivity functions of heterotrophic respiration. 
The incubation of sieved and intact soils showed distinct differences in the response of soil heterotrophic respiration to soil water saturation. The sieved soils exposed threshold-type behaviour, whereas the undisturbed soils exposed a quadratic increase of heterotrophic respiration with increasing effective soil water content. Additionally, we found significant correlations between the moisture response functions of the undisturbed soils and soil textural properties.
From the comparison of intact and sieved soil incubations we conclude that the destruction of soil structure by sieving hampers the transferability of measured soil moisture response of heterotrophic respiration to real-world conditions. For modelling purposes we suggest the use of a quadratic function between relative respiration and effective saturation for soils with a clay fraction < 20 %.