Study on the restoration effects of native vegetation Cyperus malaccensis and Phragmites australis on wetland soil invaded by Spartina alterniflora

In order to investigate the restoration process of wetland soils following invasion by Spartina alterniflora, plantings of Cyperus malaccensis and Phragmites australis were applied and the subsequent soil changes were monitored over the restoration period. Specifically, we measured a variety of soil chemical properties and soil enzyme activities within the 0 - 60 cm soil profile of five experimental plots in the Minjiang River Estuary after the eradication of Spartina alterniflora invasion. The study was designed to systematically evaluate and compare the effects of different vegetation restoration types and different restoration durations on soil characteristics. Over this monitored restoration period, several key soil parameters exhibited statistically significant changes. Specifically, the concentrations of available potassium, available phosphorus, nitrate nitrogen, and total phosphorus all marked increased at corresponding depths in both the Cyperus malaccensis plots and the Phragmites australis plots. Likewise, the activities of the enzymes acid phosphatase and urease increased significantly. In contrast, during the same restoration period and within the same soil layers, the concentration of available sulfur and the activity of the enzyme leucine aminopeptidase both showed significant decreases. These finding suggest that long-term vegetation restoration can alter nutrient availability and microbial enzyme functions in complex and distinct ways. Furthermore, in both types of vegetation plots the observed restoration effectiveness were more pronounced in the mid-depth soil layer (20 - 40 cm) compared to the top layer (0 - 20 cm) or the deeper layer (40 - 60 cm). The statistical correlation analysis of soil samples from two vegetation restoration sites further revealed significant correlations (P < 0.05) between specific enzyme activities and nutrient levels. For example, soil acid phosphatase activity was significantly correlated with the concentrations of available potassium, available phosphorus, and total phosphorus. In addition, soil urease activity was significantly correlated with available phosphorus, nitrate nitrogen, and total phosphorus. Soil leucine aminopeptidase activity was significantly correlated with available sulfur. These significant correlations suggest a close linkage between enzyme activities and soil nutrient status under restoration conditions. The interaction of vegetation type*soil depth*restoration years had a significant effect on soil chemical properties and soil enzyme activities (P<0.05). When compared to mud flat soil, both the Cyperus malaccensis and the Phragmites australis plantings were found to significantly facilitate the ecological restoration of wetland soil. Overall, after 16 years of restoration, the plots planted with Cyperus malaccensis exhibited a greater overall restoration effectiveness than those planted with Phragmites australis, with Cyperus malaccensis demonstrating a stronger soil restoration effectiveness under the long-term restoration regime.