Application of derivative synchronous fluorescence spectroscopy (DSFS) to indicate salinisation processes of saline soils in semi-arid region

Derivative synchronous fluorescence spectroscopy (DSFS), a simple, rapid and sensitive spectrofluorimetric method, was used to analyse structural components of dissolved fulvic acid (FA) extracted from saline soils, and indicate humification degree and salinisation processes. Composite soil samples of different depths were collected from different halophyte communities along a saline-impact gradient, namely, Comm. Salicornia europaea (CSE), Comm. Suaeda glauca (CSG), Comm. Kalidium foliatum (CKF) and Comm. Sophora alopecuroides (CSA). The DSFS of FA showed three peaks at around 265, 312 and 355 nm, and a weak shoulder at around 395 nm. Nine humification indices (HIXs), deduced from the DSFS were very significant in indicating humification degree of FA. FA from the CSA soils contained the most complex aromatic carbon structures and had the highest humification degree, followed by the CKF, CSG and CSE. Exchangeable sodium percentage (ESP) was closely correlated with the HIXs, and humification degree increased with the decreasing ESP. These behaviors proved that HIXs not only characterized humification degree of FA, but also indicated soil salinsation processes.