Low nutrient availability in salt marsh ecosystems can potentially limit primary productivity and subsequent carbon export to coastal waters. In temperate marshes with low external nitrogen inputs, nitrogen (N2) fixation may enhance availability of usable nitrogen to marsh plant communities and increase their growth. The effects of sub-surface soil amendment of polysaccharides on rhizosphere N2 fixation, and on plant growth and tissue characteristics of the California cordgrass, Spartina foliosa, were tested in microcosms in a tidal simulator. Polysaccharide was added as alginate extract, and rhizosphere N2 fixation and plant characteristics were measured over 9 weeks. N2 fixation rates increased 10-fold in the alginate treatment compared to controls after 1 week of exposure as a result of increased availability of a readily usable form of carbon. N2 fixation rates in amended sediment were significantly higher than rates in control sediments at weeks 1 and 3. Although plant characteristics did not differ between treatments, trends of increased number of leaves and shoots in amended plants compared to controls appeared between weeks 7 and 9. The potential for increased plant growth following an increase in N2 fixation rates warrants further investigation as it may have implications for recovery of N-limited disturbed and restored salt marshes.
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Vol. 29 • No. 3