Is Growth of Eelgrass Nitrogen Limited? A Numerical Simulation of the Effects of Light and Nitrogen on the Growth Dynamics of Zostera marina

A numerical model of nitrogen uptake and growth was developed for the temperate seagrass Zostera marina L. Goals were to evaluate the relative effects of light and nitrogen availability on nitrogen uptake and partitioning between leaf and root tissue. and to estimate nitrogen concentrations in the sedmen t and water column required to saturate growth. Steady-state predichons are quite robust with respect to a range of parameter values justified by available data The calculations indicated that roots are probably more important in overall nitrogen acquisition in most light and nitrogen environments encountered in situ, but may contribute less than 50 '/o of the total uptake in low light. The model also predcted amnlonium to be a much more important source of nitrogen than nitrate Nitrogen concentrahons required to saturate growth (even for nitrate) were estimated to be at least 50 % below concentrations commonly reported in situ, an indicat~on that nitrogen limitation of 2. marina is probably very rare in nature.