Study on the Restoration Effects of Cyperus malaccensis and Phragmites australis on Wetland Soil Invaded by Spartina alterniflora

Spartina alterniflora invasion significantly changes the physicochemical properties of wetland soils, resulting in the degradation of ecosystem functions. Taking the plots restored by different methods after the elimination of S. alterniflora invasion in the Minjiang River Estuary as the research object, the soil chemical properties and enzyme activities in the 0–60 cm soil layer of 5 plots, including Cyperus malaccensis and Phragmites australis restored for 8 and 16 years, respectively, and a bare tidal flat without vegetation restoration for 16 years, were compared and analyzed. The results indicated that: with the prolongation of restoration years, the contents of available potassium, available phosphorus, nitrate nitrogen, and total phosphorus, and the activities of acid phosphatase and urease in the soil at the same depth of 2 vegetation restoration plots all increased significantly, while the content of available sulfur and the activity of leucine aminopeptidase decreased significantly; the restoration effects of 2 vegetation types on the 20–40 cm soil were both superior to those on the 0–20 cm and 40–60 cm soils. In the soil samples restored by 2 vegetation types, soil acid phosphatase activity was significantly positively correlated with available potassium, available phosphorus, and total phosphorus; soil urease activity was significantly positively correlated with available phosphorus, nitrate nitrogen, and total phosphorus; and soil leucine aminopeptidase activity was significantly positively correlated with available sulfur. The interaction of vegetation type×soil depth×restoration years had a significant effect on soil chemical properties and soil enzyme activities. When compared to mud flat soil, both the vegetation plantings were found to significantly facilitate the ecological restoration of wetland soil, among which C. malaccensis restored for 16 a had the optimal effect.