Nitrogen dynamics of the surfgrass Phyllospadix iwatensis

Abstract

Nitrogen uptake by leaves and roots of the surfgrass Phyllospadix iwatensis Makino, growing on the subtidal rocky shore of Akkeshi Bay, Japan, was assessed by experimental measure- ments for dissolved inorganic nitrogen (DIN) uptake and field measurements for plant biomass and DIN concentrations in both the water column and sediments. Mainly, leaves of P. iwatensis con- tributed to total nitrogen uptake in fall and winter when DIN concentration in the water column was high. Otherwise, contributions of roots were higher than those of leaves in spring and summer when DIN in the water column was low. Both leaves and roots contributed to the nitrogen acquisition. How- ever, the nitrogen uptake from external media would not be enough for nitrogen incorporation in the highly productive season. Internally recycled nitrogen may play an important role in this season.