Nitrogen dynamics of eelgrass Zostera marina during a late summer period of high growth and low nutrient availability

Abstract

Total eelgrass biomass was 700 g (dry wt) m-2. Relative growth rate was 0.022 d-1 and eelgrass production was 5.6 g C m-2 d-1. Production was high in spite of low N availability in the water column and low internal N contents of plants. Nitrogen incorporation in growing tissues was 0.155 g N m-2 d-1, and the molar ratio of incorporated C to N (C:N) was 42 to six-fold higher than the average ratio reported for phytoplankton. However, due to efficient N translocation from old to young tissues, C:N in the most actively growing leaf was only two-fold higher than that of phytoplankton. Reclamation of N from old tissues supplied 12% of total N incorporation and 88% was supplied by external media uptake. Leaf and root uptake were equally important in spite of much higher N availability in the sediment porewater compared to that of the water column. Eeelgrass seems well adapted to N-poor environments because it conserves N within the plant, efficiently takes up N from both the water column and sediment, maintains high growth rates in spite of low internal N contents. -from Authors