A Model of Growth Responses by Spartina Alterniflora to Nitrogen Limitation

that the temporal changes in SGR were largely dependent on climatic factors. Although significant differences between treatments in SGR were not observed, total net dry matter production (?1 S.E.) during the growing season ranged from 10-1 + 1.9 to 41 6 + 7.2 g plant-1. (4) Differences in total plant production were attributed to differences in the ratio of growth rate of photosynthetic :nonphotosynthetic tissue rather than to changes in SGR. Quotients of root/shoot production ranged between 0.35 + 0.03 at the high rate of supply to 0.93 + 0.16 at the lowest rate of nitrogen supply. The quotient of growth rate of aerial/growth rate of below-ground biomass also showed a seasonal pattern. The growth rate of aerial biomass was initially 1.7-2.8 times that of below-ground biomass, depending on the treatment, while eventually this quotient decreased to less than 1 0. Although aerial and rhizome production were stimulated by increased nitrogen supply, total root production did not differ significantly between treatments.