Effect of low temperature and soil type on the decomposition rate of soil organic carbon and clover leaves, and related priming effect

The purpose of this study was to improve the temperature response function to be used in models of soil organic carbon (SOC) and litter mineralisation. A clay soil and a sandy soil with equivalent weather and cultivation history were incubated for 142 days at 0, 4, 8.5 or 15 °C, which is representative for the natural temperature range above 0 °C of these soils. The soils were incubated with or without 13C labelled clover leaves in gas tight chambers. In absence of added plant litter, the decomposition rate [mol CO2 (mol substrate-C)−1 day−1] of SOC followed a first order reaction and it was twice as fast in the sandy soil as in the clay soil. Contrary to our hypothesis, the relative response of SOC mineralisation rate to temperature was the same in both soils; it was well described by an Arrhenius function and it could also be approximated as a linear function of temperature. The mineralisation of clover leaves was affected by soil type, and was slower in the clay than in the sandy soil. Also the initial temperature sensitivity of the clover decomposition (to 18% decomposed) could be approximated by a linear function. SOC mineralisation was enhanced (priming effect) by the presence of clover; the relative increase was most conspicuous at 0 °C (150–250% over 142 days, depending on the soil) and decreased with temperature (+40% at 15 °C). At the start of the incubation and up to 52 days of incubation the priming effect was correlated with the amount of CO2 derived from mineralisation of clover leaves. We suggest that the effect of soil type on the diffusivity of enzymes could be an important mechanism affecting the decomposition rate and probably also the volume of soil exposed to priming around decomposing litter.In conclusion, the temperature sensitivity of the decomposition was in the order: priming < plant litter < sandy soil SOC = clay soil SOC. For the purpose of modelling, we present parameterised equations for mineralisation rates of SOC and clover leaves as function of soil temperature range 0–15 °C. Regarding modelling of priming, there is scope for relating it to litter decomposition and the influence of soil type on the diffusion of enzymes from microorganisms around the litter surface. The effect of soil type on plant litter decomposition and soil priming should be considered in models that predict nitrogen mineralisation based on the C/N stoichiometry of substrates and decomposition products.