Molecular changes of DOM cycling in forest ecosystem

Fresh water is essential for sustaining all the life on the earth. Most of the fresh water available for human is stored in forest ecosystem in the forms of soil and ground water. Therefore, the chemical compositions of fresh water could be controlled by the forest ecosystem. Dissolved Organic Matter (DOM) is one of the main dissolved components of water. Since it controls the cycling processes of both organic and inorganic matters in water by variety of physical, chemical, and biochemical interactions, chatacterization of DOM in both qualitatively and quantitatively is very important. However, molecular-level study in DOM has been behind due to technological difficulties. Over the past years, high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) which enables us to identify individual molecular species of DOM had been hugely developed and brought radical changes to the analysis of many different substances in molecular level. The purpose of this study is to observe the cycling and alteration process of DOM in the forest ecosystem substantially using FT-ICR MS. We analyzed DOM samples by FT-ICR MS to determine the molecular-level characteristics of DOM. We also analyzed dissolved organic carbon (DOC) and characteristics of fluorescence spectra to elucidate the bulk characteristics of DOM in the forest ecosystem. In forest ecosystem, DOC increased from bulk deposition (1.0~3.3 mgC/L) and throughfall (0.8~3.6 mgC/L) to soil water of the A- (4.7~28.6 mgC/L) and B-horizon (4.5~29.2 mgC/L). DOC decreased as the water percolated through the soil deeper to ground water (0.3~1.7 mgC/L). In the whole forest ecosystem, fluorescence spectra showed strong humic-like fluorescence peaks rather than protein-like peaks. Each sample's result of FT-ICR MS including bulk deposition, throughfall, soil waters in different depths, and groundwater showed different molecular characteristics between one another. These results suggest that DOM in water is changing its compositions as water passes through forest ecosystem.