Effect of the temperature on the degradation of dissolved organic matter originated from different land use – an incubation experiment

The DOM cycle in terrestrial ecosystems is of particular interest in light of climate change, as DOM is one of the largest sources of available organic carbon for microorganisms and also has numerous other ecological functions. Therefore, this study investigated the effects of temperature on the composition, transformation, and decomposition of soil dissolved organic matter (DOM) originated from different land use areas (grassland, spruce, oak, arable) in a temperate region of Hungary using a 45-day laboratory incubation experiment. The chemical composition of DOM was evaluated using PARAFAC modelling, and the changes occurring during incubation were evaluated using two-dimensional correlation spectroscopy (2D COS). Significant differences were found in the chemical composition of DOM fractions in soils with different land uses. The PARAFAC model showed that although the relative amount of the low molecular weight compounds was similar in all four soils, the DOM fraction of arable soil also contained a large amount of the C2 component (high molecular weight, aromatic compounds). In contrast, the C5 component, identified as aromatic proteins/soluble microbial product (AP/SMP), was the smallest in the DOM fraction of arable soil. According to the 2D COS analysis, biogeochemical coupling was detected as negative correlations in the synchronous spectra, with correlations between the ∼320-258, 320-278, 385-258, and 350-280 nm regions at both temperatures indicating biogeochemical coupling between low molecular weight and higher molecular weight compounds. The decomposition of spruce soil DOM differed significantly for incubation at 25 and 35 °C: at the higher temperature, DOM shifted towards organic compounds with lower molecular weights than those observed at the lower temperature.