Effect of Elevation on Phosphorus Availability In a Restored Calcareous Subtropical Wetland.

The Hole-in-the-Donut region of the Everglades National Park has undergone restoration after decades of farming and subsequent invasion by exotic species.  Prior research has determined that soil development as a result of restoration has caused a shift from nitrogen to phosphorus (P) limitation.  Little is known, however, about the involvement of hydroperiod in the process of restoration of these calcareous wetland systems. This study was designed to determine how changes in elevation affect the form and availability of P in restored sites, where lower elevations were expected to have higher levels of organic P accumulation as a result of its longer hydroperiod.  Soil P parameters (total and extractable P, P isotherms), microbial biomass P (MBP – chloroform extraction) and extracellular enzyme activities (phosphatase) were measured in surface soils (0-5 cm) during contrasting seasons (wet and dry) at sites spanning an elevation gradient in a reference wetland and at two sites in the process of restoration for 7 and 10 years.  Measured TP values were highest at the 7-year old site, followed by the 10-year old site and lowest at the reference site.  Both the reference and restored sites had a P gradient, with higher values of both TP and MBP being found in soils of the lower elevation sites.  Soil EPC₀ showed inconsistent trends with elevation and season, with contrasting patterns being found along the elevation gradient between the wet and dry seasons.  When the seasonal data were combined, there was a consistent trend of higher EPC₀ in high elevations, but this was primarily observed in the restored site soils.  Extracellular enzyme activity responded to P availability with an inverse relationship between soil P levels (TP, extractable P, MBP) and phosphatase activity.  Restoration in this ecosystem is highly dependent on development of P limitation; therefore, these results indicate elevation is also an important factor to consider when determining restoration strategies in these systems.