Ph.D. Candidate, Texas Tech University
Conference Travel Grant Type 2 (Society of Wetland Scientists)
Impact of seasonal changes on photosynthesis, nitrogen metabolism and soil nitrogen in competing invasive Phalaris arundinacea and native Carex stricta
“The invasion of Phalaris arundinacea in wetlands inhabited by the native sedge, Carex stricta, is an ideal model system to study the physiological effects of eutrophication on invasion. Present research is addressing the following questions: (1) Do seasonal changes affect nitrogen assimilatory and photosynthetic processes of each species?; (2) Is there a relationship between seasonal changes in physiological processes and soil nitrogen? Data were collected from a Carex-dominated sedge meadow and an adjacent Phalaris-dominated site in north-central Indiana during spring, summer, and autumn in 2011 and 2012. Leaf-, root- and soil-samples were collected seasonally from each site. Leaf-, root- and soil-samples were collected seasonally from each site. Phalaris exhibited more leaf nitrate reductase activity in both sites. Leaf nitrogen was higher in Phalaris compared to Carex in both sites and did not vary seasonally in Phalaris, but decreased Carex. Photosynthetic capacity for Phalaris was higher than Carex in both sites. Photosynthetic rates did not vary seasonally in Phalaris while decreasing seasonally in Carex. Soil in the Phalaris-dominated site had more nitrate than the Carex-dominated site while the Carex-dominated site had more ammonium seasonally. By autumn, the Phalaris site had more nitrate than the Carex site, consistent with greater leaf nitrate reductase activity in Phalaris. These data indicate that Carex slows down its incorporation of nitrogen into its leaves earlier in the year than Phalaris, potentially giving Phalaris an advantage to invade more space from summer into autumn. Also, the nitrate reductase and soil nitrogen data suggest that Phalaris responds better to high nitrate levels than Carex. ”