Non-native invasive species have the potential to alter riparian ecosystem nutrient cycling.  While several studies have examined nitrogen cycling changes caused by invasive species establishment, these studies examine one plant overtaking another plant rather than one plant overtaking an entire community of plants.  Riparian ecosystems are historically diverse communities that help filter runoff nitrogen.  Hence, this riparian ecosystem study compares nitrogen cycling between a monoculture of the non-native invasive, Microstegium vimineum, and a diverse community of plants.  Yates Millpond is a riparian floodplain in Raleigh, NC that has become inundated with M. vimineum.  Six pairs of side-by side plots were established at Yates Millpond in 2005; M. vimineum was continuously removed from one of the pairs, while the other pair was left as a reference control.  Plant diversity tripled after one growing season.  After one year of M. vimineum removal and natural plant recruitment, we began tracking aspects of the nitrogen cycle.  For two years, nitrogen was examined through; (1) biweekly collections of soil-water which were analyzed for nitrogen and ammonium, (2) multiple 30-day soil incubations to capture mineralization and nitrification, (3) yearly biomass harvests to determine nitrogen uptake, (4) multiple harvests of dead vegetation to determine nitrogen recycling to the soil, and (5) a year-long litterbag study to determine decomposition and nitrogen immobilization. 

Results/Conclusions

Soil water does not appear to be different in ammonium between M. vimineum removed plots and the reference controls.  Biomass N uptake differs between paired plots, depending on the type of vegetation to establish after M. vimineum removal.  Litterbags initially decomposed much more quickly for the native plants.  Yet, after one year of decomposition, M. vimineum was similar to the native vegetation in mass loss.  Overall, M. vimineum appears to affect nitrogen cycling through biomass N uptake and decomposition of decaying plant material.  This study shows that invasive plant dominance has ecosystem-level impacts to nitrogen cycling in a riparian floodplain.