Decomposition of particulate organic matter is more sensitive to temperature than the mineral associated organic matter

Temperature sensitivity of soil organic matter decomposition is important in determining the role of soils in future climate change. We isolated coarse and fine particulate organic matter (cPOM and fPOM) and mineral associated organic matter (MinOM) to represent labile, relatively less labile and stable pools of soil organic matter (SOM), respectively and incubated each at four different temperatures to determine temperature sensitivity of decomposition. The coarse particulate organic C, which comprised the smallest pool of soil organic C (SOC) was most decomposable and the mineral associated organic C that accounted for more than half of the SOC was least decomposable. At all the temperatures, the C mineralization rate followed the order cPOM ≥ fPOM > whole soil > MinOM. The disparity in the mineralization rates between cPOM and the other two SOM fractions and the whole soil widened with increase in temperature from 15° to 45 °C indicating that the labile pools of SOM were more sensitive to temperature than the stable pool. The Arrhenius, the Llyod and Taylor and the Gaussian models well-described the temperature dependence of organic matter decomposition, but the shape of the temperature response curve for different models varied considerably. Gaussian model yielded the highest decomposition Q10 and the Arrhenius model the lowest Q10 for different SOM fractions and whole soil. The decomposition temperature response of isolated SOM fractions mainly differed at temperatures below 25 °C beyond which the response tended to converge suggesting that the differential response of labile and stable pools to temperature will be foremost at temperatures below 25 °C beyond which the effect will be small and similar for SOM pools of different lability. The decomposition of cPOM fraction is likely to be influenced to the greatest extent and the MinOM at the least as a result of global warming.