Spatial and Temporal Variations of Sulfur in Plant-Soil Systems of Phragmites australis and Cyperus malaccensis Marshes in a Typical Subtropical Estuary (Min River), China

To investigate the spatial and temporal variations of sulfur (S) in plant-soil systems of Phragmites australis (PA, native invasive species) and Cyperus malaccensis (CM, common native species) marshes, in situ filed sampling was conducted in the two marshes at different seasons. Results showed that the variations of total sulfur (TS) contents in soils differed among seasons or marshes. Higher levels of TS in soils of PA marsh generally occurred in winter and summer, while those of CM marsh were observed in spring and autumn. Except for winter, the levels of TS in topsoil of CM marsh in other seasons were much higher than those of PA marsh. The variations of TS contents in soils of PA and CM marshes were dependent on the differences in physical and chemical properties (particularly electrical conductivity) of the two marshes and the differences in S absorption and utilization of the two plants. The levels of TS and the accumulation factors of S (AFS) in PA or CM differed within seasons or tissues, which could be interpreted by the differences in growth rhythm and ecological traits between the two plants. The roots/stems (R/S) and roots/leaves (R/L) ratios in PA or CM were mostly than 1, while the stems/leaves (S/L) ratios in both plants were less than 1. Allocations of S in roots of PA were generally higher than those of CM, while the values in aboveground parts of PA were much lower than those of CM. This paper found that the two plants might adopt different strategies for S accumulation and allocation to maintain their competitiveness. The PA might compete primarily by increasing the S accumulation capacities of its roots, whereas the CM might resist the spatial expansion of PA by enhancing the S accumulation capacities of its aboveground tissues.