Artificial soils to assess temperature sensitivity of the decomposition of model organic compounds: effects of chemical recalcitrance and clay‐mineral composition

Understanding the temperature sensitivity of soil organic matter (SOM) decomposition is important to predict the response of soil carbon (C) dynamics to projected global warming. There is no consensus, however, as to whether or not the decomposition of recalcitrant soil C is as sensitive to temperature as is that of labile soil C. Soil C is stabilized by three mechanisms: chemical recalcitrance, mineral interaction and physical accessibility. We used artificial soils with controlled compositions to assess the effects of chemical recalcitrance (cellulose compared with lignin) and clay-mineral composition with montmorillonite (M) or kaolinite (K) on the decomposition of model organic compounds at 2, 12, 22 and 32 degrees C. When only substrate composition was varied, the presence of cellulose enhanced the decomposition rate of lignin. Treatments with relatively large amounts of cellulose were very sensitive to temperature only at low temperatures (212 degrees C), whereas treatments with relatively large amounts of lignin had similar temperature sensitivities at all temperatures. When only clay-mineral composition was varied, CO(2) production rates were greatest in soils containing kaolinite-montmorillonite mixtures (10% K:20% M) and least in soils containing kaolinite only at temperatures >= 12 degrees C. Clay mixtures and pure montmorillonite treatments had their greatest temperature sensitivities at 2-12 degrees C, whereas pure kaolinite treatments had the greatest temperature sensitivities at 1222 degrees C. Temperature sensitivities at the highest temperatures (22-32 degrees C) were all small (Q10 < 1.1 on days 30 and 140). Artificial soils with controlled but flexible compositions may serve as simple and useful models for evaluating SOM dynamics with a minimum of confounding factors.