The Effect of Nitrogen Fertilization on the Production of Halophytes in an Inland Salt Marsh

Abstract

The effect of nitrogen fertilization on plant production, soil and plant nitrogen content, and species distribution in an Ohio salt marsh was analyzed. Seasonal measurements indicate that the three dominant species attained maximal production at different times during the growing season. Production of Salicornia europaea increased with nitrogen fertilization and it appears that reduced soil nitrogen concentrations may be responsible for the different growth forms of S. europaea found in this marsh. Shoot nitrogen concentrations of S. europaea were inversely related to the growth response to fertilization. High tissue nitrogen concentrations in Hordeum jubatum and Atriplex triangularis suggest that some factor other than nitrogen is limiting to these species. INTRODUCTION A number of studies concerning production of plants in coastal salt marsh ecosystems suggest that productivity may be limited by availability of nitrogen (Tyler, 1967; Pigott, 1969; Stewart et al., 1972, 1973; Valiela and Teal, 1974; Gallagher, 1975; Patrick and Delaune, 1976; Mendelssohn, 1979b; Haines, 1979). Smart and Barko (1980) showed that although biomass was ultimately determined by the availability of nitrogen, growth rate was affected by the salinity of the sediments. Other effects of nitrogen fertilization on coastal salt marsh vegetation include: increased allocation of resources to sexual reproduction (Jefferies and Perkins, 1977), increased levels of nitrogen in the plant material (Buresh et al., 1980; Pigott, 1969) and a change in the distribution of plants in the salt marsh (Valiela et al., 1975). While these studies suggest that nitrogen may be an important limiting factor in the productivity of coastal marshes, no studies have been done to ascertain if this is true in inland salt marshes. Studies of plant production from inland saline areas (Hadley and Buccos, 1967, Hadley, 1970) have either not examined it in relation to nitrogen limitation, or else have concentrated on the response to nitrogen additions of a single species when grown under greenhouse conditions (Cords, 1960). Lack of tidal action and differences in species composition preclude the assumption that coastal and inland salt marshes respond similarly tonitrogen addition. The Atlantic coastal marshes of the United States are generally characterized by a bay-to-upland sequence of zones consisting of perennial grasses in the low marsh, giving way to annual succulents in the higher portions of the marsh (Niering and Warren, 1980). In an Ohio salt marsh this vegetational pattern was reversed. The annual species Salicornia europaea and Atriplex triangularis form two zones bordering the center of the saline pan with the perennial grass Hordeumjubatum occurring on the outer edge of the marsh, in the area of lower salinity (Ungar et al., 1979). The objectives of this study were to determine seasonal change in plant production, the effect of the nitrate and ammonium forms of nitrogen fertilization on plant production in an inland salt marsh and to determine if nitrogen deficiencies are responsible for the difference in the growth forms of Salicornia. MATERIALS AND METHODS The study area is a saline pan located at the site of the Morton Salt Company, in the city of Rittman, Wayne Co., Ohio (long. 810 47' 30, lat. 400 57' 30:SW?4 Sec 12, T 18N, R 13W). Three vegetation zones characterize the site: a Hordeum jubatum zone, an Atriplex triangularis zone and a zone of Salicornia europaea that was divided into