The effect of soil water content, soil temperature, soil pH-value and the root mass on soil CO2 efflux - A modified model

To quantify the effects of soil temperature (T-soil), and relative soil water content (RSWC) on soil respiration we measured CO2 soil efflux with a closed dynamic chamber in situ in the field and from soil cores in a controlled climate chamber experiment. Additionally we analysed the effect of soil acidity and fine root mass in the field. The analysis was performed on three meadow, two bare fallow and one forest sites. The influence of soil temperature on CO2 emissions was highly significant with all land-use types, except for one field campaign with continuous rain. Where soil temperature had a significant influence, the percentage of variance explained by soil temperature varied from site to site from 13-46% in the field and 35-66% in the climate chamber. Changes of soil moisture influenced only the CO2 efflux on meadow soils in field and climate chamber (14-34% explained variance), whereas on the bare soil and the forest soil there was no visible effect. The spatial variation of soil CO2 emission in the field correlated significantly with the soil pH and fine root mass, explaining up to 24% and 31% of the variability. A non-linear regression model was developed to describe soil CO2 efflux as a function of soil temperature, soil moisture, pH-value and root mass. With the model we could explain 60% of the variability in soil CO2 emission of all individual field chamber measurements. Through the model analysis we highlight the temporal influence of rain events. The model overestimated the observed fluxes during and within four hours of the last rain event. Conversely, after more than 72 h without rain the model underestimated the fluxes. Between four and 72 h after rainfall, the regression model of soil CO2 emission explained up to 91% of the variance.