Abstract:To investigate the effects of ecological restoration project on variations of inorganic sulfur fractions in marsh soils during the growing season, the Phragmites australis marshes in un-restoration plot (R0), restoration plot since 2007 (R2007), and restoration plot since 2002 (R2002) of the Yellow River estuary were studied. Results showed that the contents of inorganic sulfur fractions in marsh soils were greatly altered by the ecological restoration project. Compared with R0, the levels of Water—soluble—sulfur (H2O—S) in soils of R2002 and R2007 decreased by 46.7% and 44.7%, whereas those of Adsorbed—sulfur (Adsorbed—S) and HCl—Soluble—sulfur (HCl—Soluble—S) increased by 0.4%, 116.0% and 50.1%, 29.1%, respectively. By comparison, the contents of HCl—Volatile—sulfur (HCl—Volatile—S) in soils of R2002 decreased by 8.0% while those of R2007 increased by 19.7% compared to R0. The contents of inorganic sulfur fractions in marsh soils of different restoration stages showed different variations during the growing season. There were two probable reasons. First, it was closely related to the growth rhythm of different marsh plants and the sulfur supply relationships between aboveground and belowground parts; Second, it was dependent on the variations of environmental factors (especially pH, EC, and nitrogen nutrient) caused by different ecological water supplement patterns. With increasing restoration years, both the total inorganic sulfur (TIS) content and its proportion in total sulfur (TS) content in marsh soils decreased greatly. Also, the TIS stocks in marsh soils generally decreased with increasing restoration years. The decline of TIS stock in marsh soils mainly rested with the contributions of H2O—S, Adsorbed—S and HCl—Soluble—S, and H2O—S was dominant (78%~80%). This study found that, with the gradual restoration of marshes in the Yellow River estuary and the implementation of reed harvest in winter every year, the inorganic sulfur nutrient in restoration marsh soils would gradually tend to be deficient, which might be unfavorable for the maintenance of stability and health of marshes in the long term.