Improved methodology to quantify the temperature sensitivity of the soil heterotrophic respiration in croplands

Abstract Soil heterotrophic respiration (R H ) is usually modeled using simple temperature dependence equations where the temperature sensitivity of R H could vary for different soils and climate conditions. The temperature sensitivity is expressed as a function of the base rate of heterotrophic respiration (R H − 0 ) and the respiration change rate over a 10 °C temperature shift (Q 10 ). A methodology was developed to better quantify these two parameters, and was validated using seven contrasting year-site soil respiration datasets collected in wheat fields. The data were acquired using soil respiration chambers and eddy flux towers in three mid-latitude European sites and one North American site. The first step consisted in parameterizing and initializing a semi-mechanistic process-based model then validating the prediction performance using 2/3 of the datasets. The coefficient of determinations between the predictions and the observations of daily soil respiration (R s ) was 0.71 and was 0.73 for its heterotrophic component (R H ). The second step consisted in using the daily semi-mechanistic model predictions of R H for each growing season and site to calibrate a simple empirical model describing R H response to soil temperature and water content. It was shown with the contrasting years-sites that coherent results were only obtained when a common average Q 10 value was determined prior to fit the base rate of heterotrophic respiration coefficient. Using a common Q 10 value of 2.2 provided more stable R H − 0 for each site over time. It reflected the strong relationship between the R H − 0 and the slow decomposing C in the first 30-cm soil layer. The simple empirical model, which was validated using 1/3 of the data, explained between 42% and 92% of the variability of R H over the different sites.