Pigment levels, photosynthetic performance, and tissue nitrogen levels of three age-class blade disks of Nereocystis luetkeana were followed over one complete and two partial growth seasons. Chlorophyll (chl) a, fucoxanthin, and chlorophyll c all showed high levels in fall–winter and low levels in late summer. The molar ratios also varied with much higher fucoxanthin: chl a and chl c: chl a ratios in early spring than in late summer–fall. Plots of maximum photosynthetic rates (Pmax) at saturating light intensities and initial slopes (α) derived from photosynthetic rates at subsaturating light intensities also showed seasonal variations, with maxima in August and September and minima in April. The saturating light irradiance, IR, also showed a maximum in late summer and a minimum in winter. Tissue nitrate levels were high in winter, declined to near zero levels in May–August, and increased again in fall–winter. Amino acids and total N followed a similar pattern. The older tissues farthest from the bulb had higher Pmax and pigment levels as well as internal nitrate levels than young proximal tissues. Environmental data on sea-water nitrate, photon flux density, and temperature and data on mannitol and total C are presented. It appears that there is a significant negative correlation between photon flux density and initial slope of photosynthesis and between Pmax and temperature below 15 °C. At temperatures above 15 °C, internal N concentrations, which in turn are governed by the ambient nitrate concentration, appear to become limiting. Pigment levels, especially chlorophyll a, showed a direct correlation with ambient nitrate. These data are discussed in relation to the possible biennial nature and growth strategy of Nereocystis.
Effect of Photon Flux Density and Exogenous Sucrose on the Photosynthetic Performance during <i>In Vitro</i> Culture of <i>Castanea sativa</i>