Changes in production and nutrient cycling across a wetness gradient within a floodplain forest

Floodplain forest ecosystems are highly valuable to society because of thei r potential for water quality improvement and vegetation productivity, amon g many other functions. Previous studies have indicated that hydrology infl uences productivity but that the relationship between hydroperiod and produ ctivity is a complex one. Consequently, we compared multiple indexes of pro ductivity, nutrient circulation, and hydroperiod among three communities on the Flint River floodplain, Georgia, that differed in terms of inundation frequency. We hypothesized that (a) the wettest community would have the lo west total net primary production (NPP) values because of saturated soil co nditions; (b) as wetness increases, nutrient circulation ill litterfall wou ld decrease because of the hypothesized lower productivity in the wetter co mmunity; and (c) as wetness increases, internal translocation would become more efficient. The study site was partitioned into three wetness types-som ewhat poorly drained (SPD), intermediate (I) and poorly drained (PD). We fo und that belowground biomass was greatest on the SPD, litterfall was simila r for all three sites, and that woody biomass current annual increment (CAI ) was greatest in the PD community. However, when the three variables were totaled for each site, the PB had the greatest NPP, thus disproving hypothe sis (a). For hypothesis (b), we observed that P content in litterfall, alth ough not significant, followed the predicted trend; nitrogen (N) content di splayed the opposite pattern (PD > I > SPD). As wetness increased, internal translocation became more efficient for phosphorus (support for hypothesis [c]), but the SPD community was more efficient at retranslocating N (contr adict ion of hypothesis [c]).