Impacts of nitrogen addition on variations of inorganic sulfur forms in soils of marsh in the Minjiang estuary during summer.

We investigated the distribution of inorganic sulfur forms in the typical marsh in the Minjiang estuary by conducting a field nitrogen (N) addition experiment with four N addition levels (no N treatment, N, 0 g N·m·a; low N treatment, N, 12.5 g N·m·a; medium N treatment, N, 25.0 g N·m·a; and high N treatment, N, 75.0 g N·m·a) . Results showed that the contents of water-soluble-sulfur (HO-S) and HCl-soluble-sulfur (HCl-soluble-S) in marsh soil increased with N addition levels, and the values in the N, N and N treatments increased by 36.0%, 11.6%, 7.5% (HO-S) and 12.8%, 4.8%, 9.0% (HCl-soluble-S), respectively. The contents of adsorbed-sulfur (Adsorbed-S) and HCl-volatile-sulfur (HCl-volatile-S) decreased by 45.8%, 37.0%, 4.0% and 6.1%, 1.7% and 3.3%. N addition generally increased the contents and stocks of total inorganic sulfur (TIS). Compared with the N treatment, the TIS content in the N, N and N treatments increased by 29.1%, 8.2% and 25.6%, while its stock increased by 23.1%, 13.7% and 25.6%, respectively. The elevation of TIS stock mainly rested with the contributions of HO-S and HCl-soluble-S. The variations of inorganic sulfur forms were mainly dependent on the alterations of N nutrient (especially NH-N/NO-N) and pH, and the relationships of S nutrient between plants and soils. Under N enrichment, the content and stock of TIS showed an increasing trend, indicating that the available S absorbed and utilized by plants was elevated and the increasing trend was particularly evident in the high N addition treatment (N).