Chemical differences in the non-protected carbon pool of four Hungarian soils with different vegetation types

Soil organic matter is not a homogeneous material, but can be broken down into pools with different mean residence times (MRT) ranging from days to thousands of years. Differences in the degradability of carbon pools can be explained by the different stabilization mechanisms of the carbon. Particulate organic matter (POM) is considered as a non-protected carbon pool of  organic matter, which could respond rapidly to environmental changes. To provide an insight into the changes in chemical structures of POM and the patterns of decomposition, soils from area of different types of vegetation (grass, spruce, oak and arable) were examined in a 1-year laboratory incubation at three different temperatures (15, 25 and 35 °C). The POM samples was analysed using CPMAS 13C NMR spectroscopy and it was hoped to reveal the effects of different plant cover on the chemical patterns in POM fractions. The chemical composition of the POM fraction of the soils with different vegetation differed significantly according to the results of NMR analysis. The grassland POM contains a high amount of O-alkyl compounds and relatively few alkyl-like compounds. In contrast, spruce soil POM contains high amounts of alkyl compounds. The amount of O-alkyl compounds decreased during incubation at 25 and 35 °C, whereas this was not observed at 15 °C. Similarly, the 25 °C and 35 °C incubation had a significant effect on the alkyl/O-alkyl and aryl/O-alkyl ratios, as these values increased compared to the starting conditions, while a small decrease was observed for the 15 °C incubation. This work was supported by the Development and Innovation Fund of Hungary [grant No. NKFIH 132191].