Abstract
We explored the nature and impact of competitive interactions between the salt marsh foundational plant Spartina alterniflora and invasive Phragmites australis in New England under varying levels of anthropogenic influence from nutrient loading and temperature warming. Plants were grown with and without competition in mesocosms over a four-month growing season. Mesocosms were split evenly among three levels of nutrient additions and two temperatures varying by an average of ~3° C, manipulated using small greenhouses. We measured aboveground productivity as total biomass, numbers of new stems, and mean stem height. Nutrient enrichment increased all growth parameters, while competition generally reduced aboveground biomass and the production of new stems in both species. Most importantly, smooth cordgrass suffered no negative consequences of competition when no nutrients were added and temperature was elevated. The results of this study suggest that minimizing nutrient loading into coastal marshes could be an important factor in slowing the spread of common reed into the low marsh zone of New England salt marshes as global temperatures continue to warm.
Highlights
Anthropogenic disturbances have been shown to influence successful biological invasions of many ecosystems by non-native plant species [1]; [2]; [3]
Regardless of temperature, the addition of nutrients had a positive effect on the aboveground biomass of S. alterniflora, Table 1
The results of this study suggest that the competitive relationship between P. australis and S. alterniflora may be altered under anthropogenically disturbed conditions of increased nutrient availability and temperature
Summary
Anthropogenic disturbances have been shown to influence successful biological invasions of many ecosystems by non-native plant species [1]; [2]; [3]. Important among these disturbances are increased temperatures due to global climate change and nutrient loading from upland runoff, which combine to alter the competitive dynamic between native and exotic species. Coastal wetlands are disproportionately affected by both nutrients, acting as “landscape sinks” for upland runoff [4], and elevated temperatures, which may increase rates of microbial decomposition resulting in elevation loss in the face of rising sea levels [5].
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