Comparison of enzyme activities in vegetated and nonvegetated sediments

This study focuses on the effect of aquatic plants on the changes of enzyme activities in wetland sediments. Wetland plants play essential roles both as a carbon supplier for microbes which synthesize enzymes and as a regulator for enzyme activity by modifying hydrochemistry in the rhizosphere. Although numerous studies have been carried out on soil enzymes, little information is available on the vertical distribution and temporal variation of enzyme activities affected by the presence of plants in wetlands. Our results clearly show that sediments with wetland plants exhibit significantly higher enzyme activities of Β -glucosidase, arylsulfatase, phosphatase, and N-acetylglucosaminidase (P<0.05) up to a depth of 15 cm throughout the year, whereas only lower values were observed even at the surface of sediments (0-3 cm) without plants. However, in the field, there were no statistically significant changes of enzyme activities associated with the changes of season and the vertical position along the depth (P<0.05). This indicates that the organic carbon supplemented by root exudates, root debris, and plant residue played an important role in increasing enzyme activities in the sediments with plants. The mechanisms driven by aquatic plants such as oxygen diffusion and transpiration-induced advection did not induce the short-term changes in enzyme activities. Exceptionally, the changes of sulfate availability and the increase of temperature have implications in the changes of arylsulfatase activities depending on the location (vegetated versus nonvegetated sediment) (P=0.000), season (growing season versus senescence) (P=0.042), and sediment depth (P=0.002). Since wetlands treat wastewaters with variable carbon sources, it would be beneficial to maintain increased enzyme activities in the regeneration of inorganic nutrients from organic materials. In addition, the presence of plants would vertically extend the area where the higher enzyme activities are observed and the movement of wastewater takes place and, consequently, could accelerate wetland treatment efficiency.