Soil texture controls activity of heterotrophs in soil indirectly via soil moisture

Soil organic carbon (SOC) plays a vital role in soil fertility and quality, resilience against degradation, and consequently food security. Therefore, it is crucially important to understand how current SOC stocks will be affected under future climate change scenarios. Silt soils in Western-Europe have superior soil physical quality but have lower SOC contents than sandy soils. We hypothesize that both moisture availability and aeration in silt soils strongly favour soil microbial activity, especially in warmer periods. To test our hypothesis, we have currently started a field trail of 1 year-round monitoring of CO2 emissions in Bottelare, Belgium. We replaced the upper 50 cm from the soil profile (sandy loam texture) by subsoil with sandy, sandy loam and silty textures, obtained from 50 to 100 cm depth to eliminate SOC content difference. Ground maize stalk residues were added to the plots in order to partition the total soil CO2 efflux by isotopic mass balance in situ via high-precision isotopic CO2 cavity ring-down spectroscopy (CRDS) measurements. Nitrogen was also added to avoid differences in nitrogen availability from different textures. Soil moisture at 10 and 25 cm depth is measured by TDR200 hourly. O2 and soil redox potential (Eh) is also measured to study O2 diffusions in different textures. The microbial community composition will be estimated via PLFA to evaluate the changes of microorganisms during degradation of organic carbon. The detailed and unique measurements of soil moisture levels and CO2 emission, complemented with O2, and Eh at small depth increments will allow better understanding of effects of soil texture on microbial activity in field conditions and provide valuable information for evaluating global SOC stocks