DESICCATION ENHANCED NITROGEN UPTAKE RATES IN INTERTIDAL SEAWEEDS

Desiccation increased nitrate and ammonium uptake rates upon resubmergence in late summer populations of the intertidal macroalgae Gigartina papillata (C.Ag.) J.Ag., Enteromorpha intestinalis (L.) Grev., Fucus distichus L., and Pelvetiopsis limitata (Setch) Gardn. The ratio of nitrogen uptake rates in desiccated plants to rates in hydrated plants (controls) was correlated with the position of the species in the intertidal zone. Gracilaria pacifica Abbott., the species occurring at the lowest shore level, showed no enhancement of nitrogen uptake following dessication. The high intertidal species such as P. limitata and F. distichus showed a two-fold enhancement of nitrate and ammonium uptake following more extensive dessication (> 30%) and continued uptake even following severe desiccation (50 to 60%). After the plants had been dessicated, the increase in nitrate uptake rates upon submergence lasted much longer than a similar enhancement of ammonium uptake. The duration of the enhanced nitrate uptake was similar to the time required for total rehydration but the uptake rates were not related to the state of rehydation. The potential contribution that this enhanced nitrogen uptake following desiccation could make to total nitrogen procurement for growth is discussed. The experiments were carried out in 1979 or 1980 and repeated in 1981.