The exudation of nitrate by the kelp Laminaria hyperborea, an observation during in situ incubation experiments

Abstract

During the growing season from February to May, a release of stored nitrate into the seawater medium was observed in a night and day incubation of 2–3-year-old plants of Laminaria hyperborea. A large part of the nitrate that was released appears to be assimilated by photosynthesis during the day. This is at variance with the common consensus that stored nitrate in kelp is translocated to the growing tissues at the meristem. During the non-growth season, however, there was active uptake of nitrate during both day and night irrespective of the nitrate level in the seawater medium. The uptake rate (nmole g⁻¹ h⁻¹) was found to depend on the initial nitrate level.

Key words:

• Growth cycle
• incubation
• kelp
• Laminaria hyperborea
• nitrate release
• nitrate uptake

Editorial responsibility: Mirta Teichberg