Chemical composition of labile carbon fractions in Hungarian forest soils: Insight into biogeochemical coupling between DOM and POM

Understanding how the chemical composition of dissolved and particulate organic matter (DOM and POM) is affected by environment factors is critical because these labile pools of carbon are involved in an array of bio-logical, chemical and physical processes. In this study, the chemical composition of DOM and POM was measured in 13 forest soils using UV-Vis spectroscopy, fluorescence spectroscopy with parallel factor analysis (PARAFAC modelling) and FT-IR spectroscopy. There were significant differences between the soils for the SUVA indexes, PARAFAC components and relative intensities of different IR bands. Redundancy analysis (RDA) revealed that soil parameters had a strong influence on the chemical composition of DOM and POM with high constrained variability (77.9 and 77.1 %, respectively). The pH of the soils proved to be an important controlling factor for both DOM and POM, regulating the con-centration of the C3 PARAFAC component (low-molecular-weight compounds associated with biological activity) and the aromatic compounds of POM (aromaticity, rA(1630) and rA(1515)). The silt content was the other main regulating factor controlling the chemical characteristics of the labile pool, having a strong negative correlation with the specific UV absorbance (SUVA) values of DOM due to the preferential adsorption of hydrophobic moieties. RDA analysis also revealed that there is a strong correlation between the chemical composition of POM and DOM: the relative amount of aromatic compounds (rA1515, rA1630 for aromatic rings and rA1270 for phenolic compounds) in the POM fraction was closely correlated with the SUVA values of the DOM. This clearly indicates a strong biogeochemical link between the two labile organic carbon fractions; the high molecular weight com-pounds of the DOM fraction may be derived from lignin-like structures of the POM fraction.

Automated summary

This study investigated the chemical composition of dissolved and particulate organic matter (DOM and POM) in forest soils using various spectroscopy techniques. The results showed that soil parameters, such as pH and silt content, have a significant impact on the chemical composition of DOM and POM. Additionally, a strong correlation was found between the chemical composition of POM and DOM.