LB 27-230 - Effect of global change factors on Phragmites fecundity and seedling performance

Biological invasions have accelerated with globalization, meanwhile industrialization has triggered an increase in atmospheric CO2 and nitrogen pollution. Global change factors like elevated CO2 and nitrogen disproportionately benefit invasive plants in environments ranging from arid upland systems to coastal wetlands. Phragmites australis is a wetland grass native to Eurasia that has become invasive in North American wetlands due in part to elevated CO2 and nitrogen. While elevated CO2 and nitrogen increase Phragmites growth, knowledge gaps regarding their effects on seedling recruitment exist. Most new populations of Phragmites are established through seedling recruitment, thus understanding how global change factors affect Phragmites seedling recruitment is integral in predicting invasion dynamics in a changing world. Thus, we ask: Does parental exposure to elevated CO2 and nitrogen affect seedling growth under subsequent exposure?The Phragmites invasion project at the Global Change Research Wetland (GCReW), a LTER network site at the Smithsonian Environmental Research Center, was initiated in 2010?? and consists of twelve open-top chambers (OTCs) subject to a combination of elevated (nitrogen: +25g/m2/year; CO2: + 300ppm) and ambient nitrogen and CO2. We collected seeds from these OTCs to propagate a seedling growth experiment where we exposed the seedlings to a fully factorial combination of elevated and ambient CO2 and nitrogen. We collected growth traits such as shoot number and shoot height throughout the 2-month growth phase, at the end of which above and belowground biomass, SLA, SRL, and root volume were collected.Variation in shoot height of seedlings from parent plants exposed to ambient, elevated CO2+ambient nitrogen, and elevated CO2+nitrogen was significantly affected by subsequent exposure to global change factors. We observed a CO2 fertilization effect in all seedlings, but this effect was strongest in seedlings from parent plants previously exposed to elevated CO2. The effect of nitrogen fertilization was more modest, however, seedlings from parents exposed to elevated nitrogen grew more. Seedlings from ambient and elevated CO2+ambient nitrogen parent plant produced significantly less shoots in ambient CO2+elevated nitrogen condition. Our results indicate that seedlings from parent plants with long-term exposure to elevated CO2 will produce taller shoots under elevated CO2 than seedlings from naïve parents. This suggests that as atmospheric CO2 rises into the future, selection for Phragmites genotypes that benefit more from the CO2 fertilization effect could become more dominant and with-it increase Phragmites invasive pressure.