Soil nutrient changes following a Typha x glauca invasion in a Great Lakes coastal wetland.

摘要

Invasive species are one of the major threats to the integrity and health of Great Lakes coastal wetlands. Plant invaders, such as the hybrid cattail Typha x glauca, threaten wetlands, as they can cause shifts in ecosystem structure and function and modify biogeochemical cycles and nutrient availability. Cheboygan Marsh on the coast of Lake Huron is currently undergoing invasion by T. x glauca, and soils in T. x glauca-dominated areas of the marsh have greater soil carbon and nitrogen concentrations than in areas dominated by native vegetation. This study investigated whether T. x glauca is affecting the accumulation of carbon and nitrogen in Cheboygan Marsh soils. A pollen study revealed that T. x glauca became the dominant species in Cheboygan Marsh by the late 1950s, and approximately two decades later, soil organic matter rose dramatically and reached current levels by the 1980s. A field study to test whether increased nitrogen fixation was responsible for increases in soil nitrogen found significantly higher nitrogen fixation rates in T. x glauca soils than in native or newly-invaded soils. A controlled mesocosm experiment designed to test the effects of water level on nitrogen fixation rates were inconclusive, because soil carbon, which fuels microbial-mediated nitrogen fixation, remains relatively low in the mesocosms and may take several years to decades to accumulate to field levels.