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Growth and photosynthesis responses of two co-occurring marsh grasses to inundation and varied nutrients
Citation:
Watson, E., H. Andrews, A. Fisher, M. Cencer, L. Coiro, S. Kelley, AND C. Wigand. Growth and photosynthesis responses of two co-occurring marsh grasses to inundation and varied nutrients. Botany. NRC Research Press, Ottawa, Canada, 93(10):671-683, (2015).
Impact/Purpose:
Our motivation for investigating these species and their responses to environmental conditions is the ongoing disappearance of one of the species (Spartina patens) from tidal wetlands in the U.S. Northeast. This decline in Spartina patens has been attributed to increased inundation with sea level rise, and high nutrient loads resulting from coastal development. More than half a dozen recent scientific articles have reported on this decline, and attention to this issue has intensified with increasing awareness of high regional rates of sea level. Between 1950 and 2009, sea level rise rates between Boston and Cape Hatteras were three to four times the global average, a pattern that arises from changes in the position, intensity, and width of the Gulf Stream. Another reason for increased scientific attention to S. patens declines is the potential consequences for obligate marsh-nesting birds, such as the IUCN red-listed saltmarsh sparrow, which nests almost exclusively in S. patens.
Description:
For southern New England tidal marshes, the late twentieth century decline of Spartina patens has been attributed to increased flooding associated with accelerated sea level rise and nitrogen over-enrichment from cultural eutrophication, either singly or in combination. The objective of this study was to examine the impacts of inundation and nutrient availability on growth, photosynthesis, and competitive interactions of Spartina patens and Distichlis spicata, which co-occur and are common high marsh species. While growth for both species was reduced by daily inundation, nutrient additions enhanced growth of Distichlis spicata across inundation treatments, as measured by end-of-season aboveground biomass, tiller height, and density. For Spartina patens grown in monoculture, nutrient additions did not enhance growth for the high inundation treatment. In addition, this nutrient and inundation combination adversely affected S. patens tiller density, photosynthetic efficiency and leaf CO2 uptake. For bi-species pairings, S. patens expanded relative to D. spicata under low inundation, low nutrient availability conditions, but declined relative to D. spicata under daily inundation with nutrient amendments. These findings are additionally supported by field data, which suggest that both inundation and nutrient availability play roles on structuring plant distributions. These results add evidence that S. patens stability is favored by low nutrient inputs and well-drained conditions, and supports the interpretation that this species is vulnerable to loss where high nutrient loads coincide with accelerated sea level rise. This study indicates that the interactive effects of increased inundation associated with global climate change and nutrient loading associated with coastal development may be driving well-documented historic and contemporary plant community composition changes for Long Island and southern New England coastal marshes.
