Hydrologic, Plant and Soil Controls on Microbial Biomass and Enzyme Activities in a Natural and a Restored Freshwater Marsh of Eastern Ontario, Canada

The hydrology and drainage history of freshwater marshes influence their soil properties and plant communities, which in turn affect microbial biomass and extracellular enzyme activities that regulate the biogeochemistry and functioning of the marsh. However, field reports examining the spatial differences and controls of microbial biomass and enzyme activities over intact and restored freshwater marsh landscapes are scarce.

In this study, we examined nine sampling locations spanning varied hydrologic (permanent, intermittent and no inundation), vegetative and edaphic conditions over two freshwater marshes in eastern Ontario, Canada, one intact and one restored. Aboveground plant biomass, belowground root density, soil properties, microbial biomass carbon (C _microbe ) and nitrogen (N _microbe ), and the activities of four hydrolytic extracellular enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) mineralization were determined. Correlation and redundancy analyses were conducted to identify relationships between microbial features and the environmental variables.

We show that soil extracellular enzyme activities, N _microbe and ratios of C _microbe to soil total C (C _microbe /C _soil ) and N _microbe to soil total N (N _microbe /N _soil ) were significantly lower under permanently inundated conditions in both marshes compared to intermittently and never inundated conditions. The lower enzyme activities under permanent inundation appeared to be a function of reduced microbial abundance rather than differences in soil or plant properties. Under permanent inundation, the C _microbe and microbial C/N ratio were notably higher in the intact marsh where Typha latifolia dominated than in the restored marsh dominated by Potamogeton epihydrus and Sagittaria latifolia , possibly reflecting differences in belowground plant effects on microbial properties. Phosphatase activity was positively correlated with root density ( r  = 0.57; p  < 0.01) with Carex spp. and Phalaris arundinacea having the highest. Although the soil C concentration of the restored marsh was only half of the intact one, their microbial biomass and enzyme activities were similar.

Our study revealed a strong negative impact of permanent inundation on microbial biomass and enzyme activities and noticeable vegetation‐associated effects on the microbial properties in an intact and a restored freshwater marsh. The similar microbial biomass and enzyme activities of the restored marsh indicate that restoration may effectively re‐establish microbial processes despite lower soil total carbon stocks. However, whether the higher microbial activities play a positive or negative role on the continuous burial of C requires further investigation.