New Insights into the Role of Soil Properties in Driving Cadmium-Induced Hormesis in Soil Alkaline Phosphatase under Vegetation Cover Change.

This study investigated the hormetic responses of soil alkaline phosphatase (ALP) to exogenous Cd under five different vegetation cover types in a typical coastal wetland, including mudfiat (Mud), Phragmites australis (PA), Spartina alterniflora (SA), Metasequoia glyptostroboides (MG), and Cinnamomum camphora (CC). The results showed that the activity of soil ALP was significantly enhanced by exogenous 0.3-1.0, 0.2-0.8, 0.05-0.3, 0.05-0.6, and 0.05-0.60 mg Cd /kg in Mud, PA, SA, MG, and CC, respectively. Moreover, the Horzone (an integrated indicator of the stimulation phase) of Mud and PA was significantly higher than that of SA, MG, and CC. Multiple factor analysis revealed that soil chemical properties and soil bacteria community play an important role in the hormetic effect of soil ALP to Cd stress. Soil electric conductivity (EC) and the relative abundance of Gammaproteobacteria were also identified as key drivers of the hormetic effects of Cd on soil ALP under five vegetation cover types. These findings suggest that the soil ecosystem had better resistance to exogenous Cd stress under mudfiat and native species (PA) than invasive species (SA), and artificial forests (MG and CC) when soil ALP activity was the test endpoint. Consequently, this study is beneficial for future ecological risk assessment of soil Cd contamination under divergent vegetation covers.