North Carolina Sea Grant<\/a>.<\/p>\n\n\n\nWhy should needlerush be in a rush to set down roots when it is accustomed to an area with relatively few vegetative competitors for space?<\/p>\n\n\n\n
If the Juncus<\/em> growth rate in the lab has been slow, the same cannot be said for the student researchers contributing to the study. Their academic growth has found fertile ground in Elon’s “engaged learning” philosophy and Sea Grant’s commitment to educating scientists at all academic levels. Thus, undergraduates Mariana Poole, Kirsten Rhodes, Scott Russell and Gracen Smith have research experience usually reserved for graduate students.<\/p>\n\n\n\nElon University students enjoy fieldwork. Photo by Brant Touchette.<\/figcaption><\/figure>\n\n\n\nSince last spring, Poole, Rhodes and Smith have maintained the Juncus<\/em> seedlings. Initially, the study was to have looked at how increased levels of carbon dioxide affected growth rates and salt tolerance of Juncus<\/em>. But the students quickly learned that experiments don’t always go as planned. The slow growth of the brown, needle-like marsh grass meant that once-weekly measurements became monthly. The study expanded to include Spartina alternijlora<\/em> (salt marsh cordgrass) and Scirpus robustus<\/em> (salt marsh bulrush) and those species’ responses to various freshwater and saltwater conditions.<\/p>\n\n\n\nA better understanding of how marsh plants respond to climatic and environmental change, such as fluctuations in salinity and increased carbon dioxide in the atmosphere, can have implications for coastal management and wetland restoration, Touchette explains. These plants provide a variety of ecological benefits \u2014 from stabilizing the shoreline to being the base of the food chain for numerous estuarine organisms.<\/p>\n\n\n\n
Commercial nurseries already use carbon dioxide to boost plant growth, but scientists still don’t understand how sustained atmospheric increases in the gas might affect plant growth over time, Touchette says. If growth of marsh grasses increases, will the elevation in peat that builds as the plants decay keep up with rising sea levels?<\/p>\n\n\n\n
The original question of the study remains as to how higher carbon dioxide levels associated with global warming might affect salt tolerance of Juncus<\/em>.<\/p>\n\n\n\n“Some people suspect that storms will increase in number and intensity, and that will change the landscape of coastal areas,” Touchette explains. “Marshes are likely to shift quite a lot, and salt may enter areas where water is fresh.”<\/p>\n\n\n\n
ADAPTING TO CHANGE<\/strong><\/h2>\n\n\n\nRecent die-offs of Spartina alterniflora<\/em> in southeastern and Gulf states have coincided with prolonged drought in those areas, Smith explains. Increased salinity levels have been blamed for the so-called “brown marsh syndrome” because marshland salinity rises with the diminished inflow of fresh water.<\/p>\n\n\n\nSpartina<\/em> is the lush, green marsh grass that can handle the salinity from the sea, Smith and Poole explain, while brown Juncus<\/em> hangs back in areas where water is less salty.<\/p>\n\n\n\nJuncus roemerianus<\/i> seedlings grow slowly in environmentally controlled growth chambers. Photo by Cynthia Henderson.<\/figcaption><\/figure>\n\n\n\n Because Juncus<\/em> is occasionally subjected to higher salinity levels, whereas salinity levels are more constant for Spartina<\/em>, it could be assumed that Juncus<\/em> is physiologically more adept at tolerating salinity changes. But that’s not what Smith and Poole found in their study.<\/p>\n\n\n\nSmith points to bar graphs on a research poster to show how Juncus<\/em> shuts down when exposed to salt water, while Spartina<\/em> tends to go with the flow.<\/p>\n\n\n\nPoole, a biology and music major, waxes metaphorical.<\/p>\n\n\n\n
“Spartina<\/em> is the boy scout of the coastal plants,” prepared for whatever salinity changes come its way, she says.<\/p>\n\n\n\nSmith explains that a leaf’s xylem functions like veins that pull water into the plant. But because water tends to follow areas with greater dissolved substances, water will be pulled out<\/em> of an ordinary plant suddenly subjected to salt water. Coastal plants compensate by regulating their cellular solutes so that they can stay hydrated, exchange gases and continue photosynthesis.<\/p>\n\n\n\nIn the greenhouse at Elon, Touchette demonstrates how Spartina<\/em> adjusts to salinity changes. He runs a fingernail along a green leaf and scrapes off a salty substance excreted by the plant when subjected to salt water.<\/p>\n\n\n\nIn contrast to Spartina<\/em>‘s ability to adjust to salt exposure, Juncus<\/em> has an opposite stress response, Poole notes.<\/p>\n\n\n\nSmith and Poole explain that Juncus<\/em> seems unable to “sweat out” solutes through its minute pores, or stomata. Instead, the plant decreases the amount of water vapor it gives off through its stomata to hold onto moisture. The response limits photosynthesis and productivity.<\/p>\n\n\n\nFor Juncus<\/em> that response is like, “going into its bomb shelter and eating its canned food,” Poole says.<\/p>\n\n\n\nUltimately, the study suggests high vulnerability of a valuable marsh plant to climatic or human-caused alterations of freshwater flow into the wetland ecosystem.<\/p>\n\n\n\n