Nitrite Uptake Transients and Consequences for in Vivo Algal Nitrate Reductase Assays

We conducted in vivo nitrate reductase (NR) assays with the commercially important brown seaweed, Laminaria japonica Aresch., and present evidence that significant, sustained nitrite uptake can occur under typical assay conditions. Thus, we caution investigators to determine the importance of nitrite uptake prior to conducting similar in vivo NR assays in this and other algal species. Further, we observed high initial nitrite uptake from sea‐water medium supplemented with nitrite at concentrations found in coastal seawater of Qingdao, People's Republic of China. The pattern of initial uptake was unlike that described previously as “surge uptake” or “rapid uptake” in seaweeds, but it was similar to that recently reported for rapid ammonium uptake in phytoplankton. A high initial uptake rate lasted for a few minutes, followed by a rapid decline, a transient increase and a subsequent decline to stable uptake rates after ca. 1 h. This is the first report of such initially high inorganic nitrogen uptake in seaweeds. The significance of nitrite uptake in seaweeds may have been underestimated. Seaweeds may be able to exploit short‐duration nitrite pulses, as has been observed for ammonium in phytoplankton populations.