Nutrient-use efficiency and long-term storage of nitrogen in restored wetlands in the Everglades National Park

The Hole-in-the-Donut (HID) region of the Everglades National Park (ENP) offers a unique opportunity to investigate the successional development of vegetation and the impact of macrophyte diversity on ecosystem functions, including biomass production, nutrient availability and storages.  Beginning in 1989, the ENP employed a “scraping” method to remove and control a non-native pest plant Schinus terebinthifolius which invaded the area due to disturbance from farming.  This method involves the mechanical removal of existing Schinus and underlying rock-plowed rubble and substrate leaving behind bedrock with pockets of captured substrate material.  To investigate site differences in vegetation community structure and use efficiency of nitrogen (NUE), a year long ¹⁵N stable isotope study was conducted.  In addition to investigating NUE of the vegetation, long term storages of nitrogen was evaluated in the soil, litter layer, microbial biomass communities and inorganic nitrogen pools (NH₄ and NO₃).  Soil and litter samples were collected at 24 hrs after application and 6, 12, 24, and 52 weeks and analyzed for TC, TN, TP, MBC, MBN, NO₃ and NH₄.  Live, standing dead, root, and litter vegetation samples were collected at 24 and 52 weeks; and vegetation biomass was determined at 52 weeks.  All samples collected were analyzed for ¹⁵N enrichment to determine long term storage and competition for nitrogen.  Initial analysis of the ¹⁵N data indicate that the vegetation present in the reference sites incorporate approximately 4 times more nitrogen than the vegetation present in the site restored in 2003 indicating that nitrogen is less available after restoration.