Aboveground production and nutrient circulation along a flooding gradient in a South Carolina Coastal Plain forest

Relative to effects of flooding, little is known about the influence of hyd rology-nutrient interactions on aboveground net primary production (NPP) in forested wetlands. We found that nutrient circulation and NPP were closely related along a complex physical, chemical, and hydrologic gradient in a b ottomland hardwood forest with four distinct communities. Aboveground bioma ss, NPP, biomass partitioning to stem production, growth efficiency, and so il macronutrient availability were greatest in the flooded zone, possibly b ecause of the stable hydrologic regime. In the wet transition zone, trees w ere least productive, nutrient use efficiency was highest, and N retransloc ation from foliage before abscission was "complete." Wet and dry transition zones had the lowest litterfall quality. Soil organic matter was negativel y correlated with extractable NH4-N plus NO3-N before in situ incubations a nd positively correlated with litterfall lignin/N ratios. Lignin/P and C/N ratios were positively correlated with exchangeable soil Ca and Mg, cation exchange capacity, and clay content and negatively correlated with extracta ble soil P. We concluded that periodic flooding and associated widely fluct uating soil chemistry resulted in disequilibrium between the plant communit y and environmental conditions, which led to nutrient deficiency and low NP P in the transition zones compared with the continuously flooded and mesic zones.