Calorimetry measures the response of soil organic matter biodegradation to increasing temperature

The temperature sensitivity of soil organic matter (SOM) is receiving an increasing interest due to its importance in the global carbon cycle and potential feedbacks to climate change. It constitutes a controversial topic in soil science due to different constrains involving the models employed, together with methodological limitations. It is welcome the introduction of new methods and indicators that can assess the sensitivity to temperature of the SOM macromolecule continuum on a more global basis. Calorimetry can be an attractive alternative if the SOM degradation is studied based on the heat rate under a gradient of temperature. The design of new calorimeters permits to do those measurements in real time through a temperature scan mode. We have applied and designed a preliminary protocol with this new type of calorimeters to calculate the activation energies and Q 10 values of soil samples with different recalcitrance. The calculation was run on short-term basis and continuously through a temperature gradient from 18 to 35 °C for 1 week. Results showed fast adaptation of microbial decomposition rates to increasing temperature and enough sensitivity of the method to detect changes in the heat rate involving SOM thermal properties. Labile substrates as carbohydrates showed up as potential rulers explaining E a and Q 10 changes which fitted the rule of thumb connecting both.