Temperature sensitivity of labile and stabilised organic carbon decomposition in different land uses

Abstract The temperature sensitivity of the decomposition of organic carbon pools is of key importance for modelling carbon turnover in soils. Therefore, examining the factors that determine and influence temperature sensitivity is extremely important. The decomposition of organic matter taken from three soil fractions in four land use areas (grass, spruce, oak and arable) was investigated in a 1-year incubation at 15, 25 and 35 °C. The particulate organic matter (POM) fraction corresponds to the labile C stock, the sand + aggregate fraction (S + A) to aggregate-stabilized OM, and the silt + clay fraction (s + c) to mineral-associated OM. The rate of organic matter decomposition (k) in the labile fraction significantly exceeded that of the stabilised fractions (S + A and s + c) by 23–167%. However, no significant differences were found in the decomposition temperature sensitivity (Q 10 ) values, which ranged from 2.96 to 3.71. In the cultivated soil, very high Q 10 values were detected in the aggregate fraction: 5.38. In contradiction to the kinetic theory, there were no significant differences in Q 10 between the labile and stabilised pools. The chemical composition of the organic matter was found to regulate the temperature sensitivity of OM decay: the aryl C, methoxy C and carbonyl C content was positively correlated with Q 10 , while the C/N ratio and O-alkyl C content proved to be negatively correlated with Q 10 . The results highlight the vulnerability of the aggregate fraction of cultivated soils, a significant increase in the rate of organic matter decomposition and its temperature sensitivity.