Effect of the Spartina alterniflora Root-Rhizome System on Salt Marsh Soil Denitrifying Bacteria

Nitrous oxide (N(2)O) reductase activity was used as an index of the denitrification potential in salt marsh soils. In a short Spartina alterniflora marsh, the seasonal distribution of N(2)O reductase activity indicated a causal relationship between S. alterniflora root-rhizome production and the denitrification potential of the soil system. The relationship was not discerned in samples from a tall S. alterniflora marsh. To further examine the in situ plant-denitrifier interaction in the short S. alterniflora marsh, plots with and without living S. alterniflora were established and analyzed for N(2)O reductase activity 5 and 18 months later. In the plots without living Spartina there was a significant reduction in the soil denitrification potential after 18 months, indicating that in the SS marsh the denitrifiers are tightly coupled to the seasonal production of below-ground Spartina macroorganic matter. In plots with intact Spartina, the soil denitrification potential was not altered by NH(4)NO(3) or glucose enrichment. However, in plots without living Spartina, there were significant changes in soil N(2)O reductase activity, thus indicating that the plants can serve as a "buffer" against this form of pulse perturbation.