Impact of different type of organic fertilizer on the temperature sensitivity of microbial processes related to the biodegradation of carbon

Soil microorganism’s response to climate change will determine the intensity of soil-atmosphere feedbacks. A parameter that allows to better understand microbial physiology is carbon use efficiency (CUE). While it has been suggested that soils with higher CUE should lead to an increase in SOM residence time, we still lack in understanding how CUE is impacted by increasing temperatures within soils undergoing distinct fertilization regimes. To this end, we conducted temperature-sensitivity laboratory incubation experiments at six different temperatures (5, 10 15, 20, 25, 30°C) on soils from a 20 years long-term field experiment, using various organic wastes (sewage sludge, green waste and wood chips co-compost, manure, and biowaste compost). We evaluated microbial physiology using the H 2 18 O-CUE method, measured extracellular enzymatic activities, and used the ramped-thermal Rock-Eval (RE) pyrolysis to evaluate the quality and quantity of SOM. To differentiate the temperature sensitivity of more labile versus less labile SOM, we performed the temperature assays on fresh soil and soils preincubated for 3 months at 20°C. Our results show distinct SOM, with soils receiving composted biowaste having a stronger thermostable SOM signal. We did not observe any difference in CUE between the different treatments, but a general decrease with temperature. However, the biowaste compost and manure treatments show higher growth rates. No effect of the 3-month pre-incubation was observed on the temperature sensitivity of microbial respiration. Our current work continues to explore the links between SOM quality and microbial temperature sensitivity response.