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

Abstract

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.