Al(III)-binding properties at the molecular level of soil DOM subjected to long-term manuring

Abstract

Advanced knowledge of the binding of dissolved organic matter (DOM) with aluminum (Al) ions is essential for understanding the toxicity, mobilization, and fate of Al in acidic soils. In this study, parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) were combined to characterize the Al(III)-binding properties of DOM extracted from farmland topsoil (0–20 cm) subjected to long-term application of chemical fertilizers (CF) or manure (M). The total Al concentration of solid soil in the M treatment (7.57%) was lower than that in the CF treatment (8.56%). In contrast, the organic-complexed Al concentration of the aqueous DOM extract in the M treatment (79 μmol/L) was dramatically higher than that in the CF treatment (0.9 μmol/L). Compared with CF treatment, PARAFAC-derived components in soil DOM from the M treatment had stronger Al(III)-binding affinities (log KM value), suggesting that soil DOM from long-term manuring has stronger potential to mobilize Al in acidic soils than that from chemical fertilizer applications. Fourier transform infrared (FTIR) spectroscopy coupled with 2D-COS revealed that soil DOM from the M treatment exhibited more Al(III)-binding sites than that from the CF treatment. In addition, aliphatic –OH groups showed the fastest response to Al(III) binding. These results provide a more detailed theoretical basis, at the molecular level, of the interaction mechanism of Al(III) with soil DOM, which is helpful for a deeper understanding of DOM-influenced biogeochemical cycling in farmland subjected to long-term manuring.