Fluorescence Spectroscopic Characteristics and Cu2+-complexing Ability of Soil Dissolved Organic Matter

Abstract

Extracted and dialyzed from four kinds of soil and chicken manure, DOM samples were analyzed to investigate their molecular weight distribution, chemical structure characteristics and the metal binding capacity. The results showed that the integral area of the molecular weight of chicken manure DOM was much higher than those of other samples, which indicated the high content of organic matter. And the peat soil followed it. The integral areas of dark brown soil, cinnamon soil and black soil were low, accounting for only 4.5%-5% of chicken manure integral area. The integral area of chicken manure DOM in middle molecular weight fraction accounted for about 34.1% of the total material, while those in low molecular weight and high molecular weight fractions accounted for about 41.7% and 24.2%, respectively. The protein-like fluorescence peaks (Ex/Em=240-270/300-350 nm) were present in all samples, and absent in middle and high molecular fractions (Mr>500) for dark brown soil. The visible fulvic acid-like florescence peaks (Ex/Em=325/420 nm) observed in peat soil, and the florescence peaks of black soil in the middle and high molecular fractions (Mr>500) both had a red shift phenomenon. The DOM of chicken manure had the UV-fulvic acid-like florescence peaks similar to black soil, and the visible fulvic acid-like florescence peaks similar to peat soil. Furthermore, it had a kind of protein-like fluorescence peak (Ex/Em=280/350 nm) that was absent in the middle molecular weight fraction (500< Mr< 12000). The Cu2+ complexation constant was 4.13 for peat soil, and smaller for other three kinds of soil (between 2.10 and 3.10). Chicken manure showed the greatest ability to bind Cu2+ with a resulting complexation constant of 6.66, indicating the importance of the unique peak, protein-like fluorescence peak, in the chicken manure of the low and high molecular weight fractions.