C-14 UPTAKE BY THE MARINE ANGIOSPERM PHYLLOSPADIX-SCOULERI

Rhizomes and attached leaves of P. scouleri Hook. were collected in the intertidal zone along the central California USA coast and exposed to a solution of NaH14CO3 in seawater under controlled laboratory conditions. Over a 90 min period roots and rhizomes absorbed very little 14C compared to leaves. Translocation during that time was minor. Plants pretreated with the photosynthetic inhibitor DCMU [(3,4-dichlorophenyl)-1,1-dimethylurea] showed no 14C uptake, indicating that under normal circumstances the C which is absorbed by leaves is fixed and accumulates as photosynthate. The rate of gross photosynthesis was about 13 mg CO2 g dry wt-1 h-1. Gross photosynthesis of wet leaves exposed to 14CO2 in air was significantly less than leaves exposed to NaH14CO3. The effect of a leaf-grazing limpet (Notoacemea paleacea) on leaf anatomy and 14C uptake is discussed.