Influence of extractants and filter materials in the extraction of dissolved organic matter (DOM) from subtropical agricultural soil

Abstract

The dissolved organic matter (DOM) plays an important role in ecological processes in agricultural ecosystems. However, composition of DOM extracted by different methods remains unclear. In this study, pyrolysis–gas-chromatography/mass spectrometry (Py-GCMS) was used to investigate the content and chemical composition of DOM extracted by aqueous K₂SO₄ or H₂O and filter paper (FP) or membrane (FM). The results showed that dissolved organic carbon (DOC) content extracted by K₂SO₄ was 0.83–11.2 times higher than that extracted by H₂O, while it increased by 10.1–75.0% when filtered by FP compared to that filtered by FM. Compared with the H₂O extract, the K₂SO₄ one contained lower proportions of aromatic compounds. The relative proportions of hydrophobic compounds in the K₂SO₄ extract (9.7–89.7%), were higher than in H₂O one (2.6–63.5%), whereas the proportions of hydrophilic compounds exhibited the opposite trend (p<0.05). The content and complexity of the DOM extracted by the FP-K₂SO₄ method was higher than that obtained by FM-H₂O one. Taken together, the K₂SO₄ and H₂O extractants affected both the quantity and quality of DOM, whereas the FP and FM filter materials only influenced the DOC content (p<0.05). Consequently, effect of the extraction method on DOM properties should be considered when studying DOM composition and corresponding ecological processes.