An evaluation of surge uptake capability in the giant kelp (Macrocystis pyrifera) in response to pulses of three different forms of nitrogen

This study examined the capacity of the giant kelp, Macrocystis pyrifera, to exhibit surge uptake as a mechanism to enhance nitrogen assimilation during seasons when nitrate is depleted. Surge uptake of nitrate, ammonium, and urea was assessed in the spring and summer with whole-blade incubation experiments using (15) N tracers. The incubation experiments showed evidence of surge uptake lasting up to 5 min for ammonium and 1 min for nitrate during the summer only. Giant kelp showed little capacity for surge uptake of urea regardless of season. The ecological importance of the patterns of surge uptake observed for ammonium and nitrate, however, is questionable, given the small scale and ephemeral nature of ammonium pulses most likely experienced by giant kelp, and the longer duration pulses of nitrate associated with internal waves and upwelling. Rather it seems more likely that uptake of ammonium and urea at ambient concentrations, combined with normal uptake of nitrate during longer duration pulses of high concentrations, sustains giant kelp growth during seasons when ambient concentrations of nitrate are low.

Automated summary

Giant kelp exhibited surge uptake of ammonium and nitrate in summer, but had limited capacity for surge uptake of urea. The ecological importance of surge uptake patterns for ammonium and nitrate is questionable, as the small scale and ephemeral nature of ammonium pulses, together with longer duration pulses of nitrate, may sustain giant kelp growth during seasons with low nitrate concentrations.