Growth and Resource Allocation Responses of Spartina alterniflora Loisel. to Three Levels of NH4-N, Fe, and NaCl in Solution Culture

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Abstract
Along tidal creek banks of East Coast salt marshes, stands of S. alterniflora Loisel., cordgrass, are taller, greener, and have greater standing crops than stands at higher elevations in the marsh. Gradients of salinity, Fe, and NH3 were suggested as underlying causes. Seedlings were grown for 11 wk in a solution culture factorial experiment at 3 levels each of NH4-N (0.14, 1.4, and 14 mg N/l), Fe (0.1, 1.0, and 10 mg/l) and NaCl (5, 20, and 40 g/l). Plant height, total dry weight, rhizome length, rhizome weight, and root weight were significantly affected by NH4-N and by NaCl but not by Fe concentrations. In general, increasing NH4-N promoted growth except at the highest salinity. Shoot-to-root ratios indicated decreased resource allocation to root production with increase of both NH4-N and NaCl. Shoot-to-rhizome weight ratios showed allocation to rhizomes was little affected by salinity but was favored by increased amounts of NH4-N and Fe. For the 3 factors studied, results suggested that future field studies of S. alterniflora should focus on relations of process rates to variations in concentrations of N and of salt rather than of Fe.