Nitrate uptake and duration of internal nitrogen reserves in the kelp Eisenia arborea

Abstract

Abstract Eisenia arborea is the kelp species that is distributed furthest south in the northern hemisphere. Although much is known about how the giant kelp, Macrocystis pyrifera, responds to nutrient-poor conditions, very little is known about Eisenia, even though these two kelps share much of their habitat. The response of E. arborea to environmental nitrogen shortage was explored by determining short-term nitrogen uptake in the laboratory, duration of internal nitrogen reserves in nutrient-poor tanks, and recovery of reserves during weekly pulse fertilization with nitrate. Nitrate uptake was linear for at least 3 h at all concentrations and did not exhaust nitrate in the media. In both experiments in nutrient-poor outdoor tank cultures, regardless of initial tissue nitrogen concentrations, tank nitrate fell to undetectable levels after 4 weeks, and internal tissue nitrogen reserves fell to 1.0% of dry weight within 5 weeks. Low internal reserves were replenished in fertilized treatments, which had significantly greater dry weight tissue nitrogen (up to 1.3%) than thalli in non-fertilized tanks, in which algae tissue nitrogen fell to and remained constant at 1%. We conclude that the nitrogen physiology of E. arborea is adapted to survive a maximum of 5 weeks in the field under nutrient-poor conditions, similar to the giant kelp M. pyrifera.