Discussion

 The nitrogen mineralization (Nmin) process in high soil moisture conditions was dominated

by ammonium production (NH4 ), with low concentrations of nitrate being measured. The net

nitrification rates represented 50% of the production during 2002 and less than 25% during 2005.

The net nitrogen mineralization rates were 10 magnitudes greater during 2002 compared to 2005

(Table 3-3). Similar results between NO3- and NH4' Were meaSured in a study comparing xeric,

mesic, and wet longleaf pine sites in southern Georgia (Wilson et al. 2002).

 When Nmin became positively correlated with soil moisture and SOM during the mid-age

and mature age classes, nitrate levels (NO3-) became negatively correlated to ammonium (NH4 )

production. The dynamics indicates a portion of the NO3~ WAS converting to NH4' during

saturated conditi ons. Thi s conditi on might b e indicating the di ssimilatory nitrate-reducti on-to-

ammonium (DNRA) process is taking place during flooded conditions. Little dinitrogen (N2) gaS

is lost to the atmosphere or NO3- by leaching when the DNRA pathway is dominant.

 Flooding causes a lower redox potential (Eh < 0.6), and with a sufficient supply ofNO3

and labile carbon, DNRA became the preferred pathway over denitrification, resulting in the

enriched pool of NH4' (Stevens et al. 1998). Investigators examined the changes in nitrogen and

phosphorus availability in longleaf pine sites from wetlands through an ecotone to upland sites,

and they measured higher levels of nitrate and phosphorus taken from soils in the middle of

wetland sites than found in the ecotone or upland sites. However, the upland sites had higher

amounts of labile nitrate than the wetter sites (Craft and Chiang, 2002).

 The anaerobic conditions and a high supply of non-labile nitrate in wet longleaf pine sites

are conducive to DNRA. During anaerobic conditions, the DNRA pathway provides NH4' to

plants and microbes, requiring less energy to assimilate than NO3~ aSSimilation (Silver et al.

2001). The characteristics favoring DNRA over denitrification are high rainfall, a high C:N ratio,