Growth Responses of Coastal Halophytes to Inorganic Nitrogen

Intraand interspecific variation in growth responses to inorganic nitrogen (NH+ or NO-) has been studied in halophytic species grown in sand culture. Populations of Aster tripolium, Plantago maritima, Salicornia europaea agg. and Triglochin maritimna from the upper levels of a salt marsh at Stiffkey, Norfolk, have slower growth rates than corresponding populations from a low marsh at the same locality. Populations of Aster tripolium and Plantago maritima from the upper marsh away from drainage channels grow slower than populations close to channels. Species characteristic of the low marsh such as Halimione portulacoides, Aster tripolium and Suaeda maritima have fast growth rates compared with the rates of species abundant in the upper marsh such as Armeria maritima and Limonium vulgare. Although there is seasonal variation in the concentrations of soluble inorganic nitrogen in the sediments of the two marshes, the values obtained are similar for both marshes, but the upper marsh, unlike the lower marsh, becomes hypersaline in summer. It is suggested that the slower growth response to nitrogen of plants from the upper marsh away from drainage channels is the result of selection for plants with relatively low growth rates, which are able to survive the period of stress during the summer months when the soil is hypersaline.