Transient Photosynthetic Responses of Nitrogen‐deprived Petalonia Fascia and Laminaria Saccharina (Phaeophyta) to Ammonium Resupply1

Petalonia fascia (Müller) Küntze and Laminaria saccharina (L.) Lamouroux cultured in N‐free medium exhibited transient depressions in light‐limited and light‐saturated gross O2 evolution within 0.3 h following ammonium resupply. Recovery of photosynthesis to pre‐resupply rates required 24 h. After 6‐9 d of ammonium resupply, photo synthetic rates of N‐deprived algae were similar to those of control plants grown with nitrogen. This study demonstrates that N‐deprived macroalgae exhibit suppressed photosynthesis upon nitrogen resupply similar to many microalgal species. The apparent slowness of short‐term recovery from nitrogen‐elicited photo synthetic suppression may have ecological consequences for macroalgae under conditions of patchy nutrient supply.