Temperature Response of Soil Organic Matter Decomposition Rates: Construction and Applications of a Temperature Gradient Block

Soil is the Earth's largest carbon (C) reservoir, holding nearly twice as much C as the atmosphere. Climate change-induced temperature increases could enhance soil organic matter (SOM) decomposition, potentially releasing carbon dioxide (CO2) into the atmosphere, thus resulting in a positive feedback to climate change. This presents the question: how can we define the response of SOM decomposition rates to short-term changes in temperature? Can we utilize this data to fit mechanistically defined equations in Earth system models for climate predictions? Most research to date has focused on laboratory soil incubations at different discrete temperatures. This, however, does not result in a detailed temperature response curve, which is required to test novel hypotheses imposed by the latest developments in the field, such as the macromolecular rate theory (MMRT). In this paper, we introduce a temperature gradient block, modified and improved from earlier work, detail its construction process, and provide a detailed explanation for its utilization. The temperature gradient block is an aluminum block with four rows of 22 discrete holes, allowing the simultaneous incubation of 88 microcosms (60 mL vials). The block is cooled at one end and heated at the other, creating a linear temperature distribution. It provides 22 discrete temperature points along a user-defined range within limits of 0 to 90 °C. After 3.5 h of incubation, CO2 production is measured from each of the 88 microcosms. Results demonstrate that the block produces the user-defined temperature gradient and facilitates the construction of temperature response curves of SOM decomposition. Additionally, the data collected from this setup can be used to test and develop new hypotheses and theories regarding the impact of temperature changes on SOM decomposition rates, an area of increasing importance in the context of climate change.