Lasting effect of soil warming on organic matter decomposition depends on tillage practices

Global warming accelerates soil organic matter (SOM) decomposition with strong feedback to atmospheric CO2. Such an effect should be especially important for no-till agricultural practices, where SOM accumulates in the topsoil as compared with conventional tillage. We incubated soil samples (0–5 cm) at three temperature levels (15, 21 and 27 °C) from long-term till and no-till systems that were in situ warmed and non-warmed to assess the temperature sensitivity of CO2 efflux, labile organic carbon and extracellular enzyme activities. Thermal adaptation to prolonged warming was observed resulting in a lasting effect on SOM decomposition. On average, 26, 14 and 12% more CO2 was emitted at each incubation temperature from the warmed soils compared to the non-warmed soils. The Q10 value was lower for the warmed than the non-warmed soils. Soil microbial biomass C and dissolved organic C declined with warming. The activities of three extracellular enzymes, β-glucosidase, chitinase, and sulfatase, were higher under warming and no-till as compared to non-warmed and tilled soil. We concluded that the increased SOM decomposition due to the stimulation of microorganisms by warming was long-lasting. Predictions of C accumulation in the topsoil by no-till farming should be taken with caution, as this C pool is especially vulnerable to global warming.