Spatial variations in the molecular diversity of dissolved organic matter in water moving through a boreal forest in eastern Finland

Jun’Ichiro Ide,Yuko Sugiyama,Miyako Hara,Leena Finér,Mizue Ohashi,Katsutoshi Takahashi,Sirpa Piirainen,Nobuhide Fujitake,Keitaro Yamase,Nobuhito Ohte,Pirkko Kortelainen,Mina Moritani

doi:10.1038/srep42102

Abstract

Dissolved organic matter (DOM) strongly affects water quality within boreal forest ecosystems. However, how the quality of DOM itself changes spatially is not well understood. In this study, to examine how the diversity of DOM molecules varies in water moving through a boreal forest, the number of DOM molecules in different water samples, i.e., rainwater, throughfall, soil water, groundwater, and stream water was determined using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in Norway spruce and Scots pine stands in eastern Finland during May and June 2010. The number of molecular compounds identified by FT-ICR MS (molecular diversity) ranged from 865 to 2,194, revealing large DOM molecular diversity in the water samples. Additionally, some of the molecular compounds were shared between different water samples. The DOM molecular diversity linearly correlated with the number of low-biodegradable molecules, such as, lignin-like molecules (lignins), but not with dissolved organic carbon concentration. The number of lignins shared between different sampling locations was larger than that of any other biomolecular class. Our results suggest that low-biodegradable molecules, especially lignins, regulate spatial variations in DOM molecular diversity in boreal forests.

Highlights

Clear-cutting was reported, suggesting that forestry operations affect the chemical composition of DOM19
Each Dissolved organic matter (DOM) molecular compound was assigned to one of seven biomolecular classes (i.e., lipids, proteins, aminosugars/carbohydrates (As/Ch), unsaturated hydrocarbons (UH), lignin-like molecules, tannin-like molecules, or condensed aromatic structures (CAS)), or it was noted that it could not be assigned to any class
The results of the FT-ICR MS analysis revealed that thousands of different DOM molecules existed in each water sample collected from our study site, i.e., Kangasvaara catchment (Fig. 1a)

Summary

Introduction

Clear-cutting was reported, suggesting that forestry operations affect the chemical composition of DOM19. Kalbitz et al.[29] investigated changes in the chemical composition of DOM samples extracted from different materials, including maize straw, forest floors, peat, and agricultural soils, during a 90-day incubation using several methods, such as ultraviolet absorbance, fluorescence emission spectroscopy, and Fourier transform infrared spectroscopy. Their results indicated that the partial degradation of higher molecular weight compounds, such as lignin dimers and alkylaromatics, increases the proportion of lower molecular weight compounds, such as lignin monomers and phenols, which are biodegradation products. Our hypotheses were as follows: 1. The number of molecular compounds detectable by FT-ICR MS (i.e., molecular diversity) and subsequently the number of each biomolecular class vary with water movement (i.e., rainwater to stream water via throughfall, soil water, and groundwater)

Objectives

Methods

Results

Conclusion