The impact of sieving on heterotrophic respiration response to water content in loamy and sandy topsoils

• Intact cores and sieved material were incubated.
• Soil water retention curves of the intact cores and sieved material were measured.
• We detected distinct differences in the heterotrophic respiration response to soil water content.
• A plateau-type behaviour of the sieved soils and a quadratic increase of respiration for the intact cores was observed.

Understanding the relation between soil heterotrophic respiration and water content is important for the prediction of climate change effects on soil CO2 emissions. In order to quantify the influence of air-drying and sieving with 2 mm meshes on the heterotrophic respiration response to soil water content we incubated intact cores and sieved samples of two loamy and two sandy soils for six levels of effective soil water saturation. We further determined soil textural properties and the soil water retention curves of the soils with the intent to identify links between soil physical characteristics and moisture sensitivity functions of heterotrophic respiration. The incubation of sieved and intact soils revealed distinct differences in the response of heterotrophic respiration to soil water content. The sieved soils exposed a threshold-type behaviour, whereas the undisturbed soils exposed a quadratic increase of heterotrophic respiration with increasing effective soil water saturation. Further, we detected significant correlations between the moisture response functions of the undisturbed soils and soil texture. From the comparison of sieved and intact 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%.