of 1.0 umole photons. m' 2 .day" 1 , with Ammen plants achieving net 

 photosynthesis at a photon flux density (0.576 mole photons. m" 

 2 .day 1 , 10 umole photons. m' 2 .s" 1 ) at which coastal plants 

 experienced a net carbon loss. Above 1 mole photons. m" 2 .day 1 the 

 coastal plants achieved higher rates of net carbon assimilation 

 than Ammen Laminar ia . Similar patterns were obtained from the P 

 vs I data of the 1, 15, and 30 m transplanted plants (data not 

 shown) . 



Figures 13, 14, and 15 respectively show the cellular 

 contents of mannitol, amino-N and nitrate in the Ammen and coastal 

 Laminaria initially and following growth at the transplant sites. 

 Initial mannitol levels in the Ammen plants were low (13.58 

 umole. g f wt' 1 ) , whereas those for the coastal Laminaria were high 

 (281.0 umole. g f wt " 1 ). Ammen plants transplanted to the 1 and 

 15 m coastal sites exhibited considerable increases in cellular 

 mannitol levels to between 350 and 410 umole. g f wt' 1 , whereas 

 those at the 30 m Ammen site had much smaller increases in 

 mannitol (62.4 umole. g f wt" 1 ) . Mannitol levels in the coastal 

 plants remained high at all transplant sites and did not differ 

 significantly from the initial value. Initial amino-N levels were 

 much higher in the coastal than Ammen Laminaria (40.96 cf. 10.92 

 umole. g f wt" 1 , respectively) (Figure 14). Amino-N levels were 

 lower in the 1 and 15 m coastal sites and did not differ 

 significantly between the groups. At the 30 m site the Ammen 

 plants had higher levels of amino-N than the coastal group (14.35 

 cf. 8.61 umole. g f wt" 1 , respectively). Nitrate contents were 

 undetectable in the coastal Laminaria population at all sites 

 except for the 30 m transplants which had 1.95 umole. g f wt" 1 . In 

 contrast the initial Ammen plants had an initial cellular nitrate 

 pool of 3.12 umole. g f wt" 1 which increased to 59.11 umole. g f 

 wt" 1 at the 30 m site but which was lost at the 1 and 15 m coastal 

 transplant sites. 



Cellular nitrate reductase activities of the Laminaria plants 

 are shown in Figure 16. Initially, coastal plants had 

 significantly higher activities of this enzyme than Ammen plants 

 (0.348 cf. 0.043 umole. g f wt' 1 .hr' 1 , respectively). Activities 

 were similar at the 1 and 30 m transplant sites (0.126-0.156 and 

 0.025-0.031 umole. g f wt" 1 .hr" 1 at 1 and 30 m, respectively) but 

 were different at the 15 m site where Ammen plants had very low 

 activities (0.007 umole. g f wt" 1 .hr" 1 ) compared to the coastal 

 group (0.092 umole. g f wt" 1 .hr' 1 ) . 



DISCUSSION 



The results presented here suggest that genetic differences 

 do exist in the photosynthetic physiology of Ammen and coastal 

 Laminaria plants. Overall, Ammen plants have lower maximum rates 

 of photosynthesis (Fig. 3), lower respiration rates (Fig. 7) and 

 lower light compensation points (Fig. 6) than the coastal L. 

 diqitata population. These differences persisted in transplanted 

 plants, grown under similar light conditions, suggesting either 



38 



