EFFECTS OF NITRATE CONCENTRATION ON THE GROWTH AND PHYSIOLOGY OF LAMINARIA SACCHARINA (PHAEOPHYTA) IN CULTURE 1, 2

Observations have been made on photosynthesis (oxygen evolution) and seasonal fluctuations in antenna pigments in 2 seaweeds which CO-occur in the vicinity of Beaufort, North Carolina, USA. Gracilaria foljifera (Rhodophyceae) and Ulva sp. (Chlorophyceae) were grown in outdoor continuous-flow cultures a t ambient incident light (I,) and .13I,. Pigment contents and accessory pigment: chlorophyll a ratios were higher at ,131, than at I,. Total pigment levels were correlated with soluble N in seaweed tissue. During the spring/summer growing season, pigment levels were low and peaks i n pigment content followed nutrient pulses in the ambient seawater. Pigment contents in both Species were higher in winter In G. foliifera, the R-phycoerythrin: chl a ratio was highest in fall-winter and lowest in summer. The higher growth rates achieved by Ulva sp. reflected the higher rates of photosynthesis measured in this species. Photosynthesis-light curves showed that Ulva sp. had a higher photosynthetic capacity (P,, = 430 ymol O2 evolved g dry wt-' h-') and initial slope (in shadeacclimated plants) than G. folijfera (P,, = 160 pm01 0, evolved g dry wt-' h-'). Increased pigment contents in shade plants of both species resulted in enhanced photosynthetic performance at subsaturating light intensities. It appears that the effect of transient pigment increases in the summer was to increase P, , , temporarily while, in winter, the effect was to limit the decrease in integrated net photosynthesis in the face of decreased light and temperature.

Section: Discussionmentioning

confidence: 99%

Ecological Growth Strategies in the Seaweeds Gracilaria foliifera (Rhodophyceae) and Ulva sp. (Chlorophyceae): Photosynthesis and Antenna Composition

Rosenberg¹,

Ramus²

1982

“…In Fucus virsoides (Zavodnik 1973) and in the red alga Hypnea musciformis (Durako & Dawes 1980) thallus degradation occurred when pigment and protein levels were low. It has been suggested that a high pigment content provides a large reservoir of amino-N that can be used to buffer the seaweed against a temporary reduction in N supply (Chapman et al 1978, Probyn 1982, Smith et al 1983) and that accessory pigment concentrations are responsive to light as well as to ambient nitrogen (Shivji 1985). In Pleurophycus gardneri, however, the senescent blade contains a higher amount of photontrapping chlorophyll a per unit area than the young blade, but produces only half the amount of mannitol (Fig.…”

Section: Discussionmentioning

confidence: 99%

Aspects of carbon metabolism in relation to autumnal blade abscission in the kelp Pleurophycus gardneri (Phaeophyceae, Laminariales

Germann¹

1989

Pre-abscission changes in the deciduous kelp Pleurophycus gardneri involve a gradual decrease in dry weight, mannitol and laminaran content. These carbon compounds decreased from about 18% (dry weight) to 4 % prior to blade abscission, while the perennial structures, stipe and holdfast, showed a concomitant increase in mannitol and dry weight towards autumn. In November, at the time of new blade outgrowth, mannitol content peaked in stipe and holdfast with 12 and 1 8 % , respectively. Laminaran accounted for less than 2 % in all thallus parts and showed no measurable seasonal variation. Pigment levels of the blade increased with progressing senescence and were at maximum just prior to blade abscission. The photosynthetic performance of the blade revealed saturating irradiances of about 50pE m-2 S-' and a compensation irradiance of 2.5 to 3~t E m-2 S-' measured in April. h g h t saturation of the stipe was at 38 pE m-2 S-' and of the haptera at 23 pE m-2 S-' while compensation irradiances were at roughly 8 FE m-2 S-' for both perennial parts. It is suggested that new blade outgrowth requires 11ght-carbon fixation. No acropetal translocation of the abundant carbon store of the perennial structures was observed The deciduous habit of P. gardneri reflects a shade-adapted growth strategy. The perennial parts are involved In the overall physiology of the plant and have similar seasonal fluctuations in their constituents to those of the blade. The described growth strategy is novel among perennial kelp species.

“…Nitrate pools do occur in some kelps. The size of the pool seems to fluctuate seasonally with the ambient nitrate concentration and is utilized after ambient nitrate levels decline (Chapman & Craigie 1977, Chapman et al 1978, Wheeler & North 1981. The negative growth rates of northern plants at southern sites with low nutrient concentrations and their high sensitivity to subsaturating nitrate conditions might be expected, because plants at the northern sites rarely experience these conditions.…”

Section: Factors Influencing Growthmentioning

confidence: 99%

Geographic variability in form, size and survival of Egregia menziesii around Point Conception, California

Blanchette¹,

Miner²,

Gaines³

2002

Intra-specific morphological variability is common among many species of plants, and is particularly common among marine algae. Populations of the kelp Egregia menziesii (Turner) Areschoug are known to be extremely variable in form, and variability in this species is well-correlated with geographical distribution. Populations north of Point Conception, California, are characterized by individuals having thick, tough, wide stipes and small blades, whereas populations south of Point Conception are characterized by individuals having thin, smooth stipes and large blades. Point Conception (hereafter PC) is a well-known biogeographic boundary for many marine species. The region north of PC is typified by cold, nutrient-rich water favorable to plant growth, but also by high wave exposure, increasing the likelihood of plant breakage or dislodgement. The region south of PC is characterized by warmer, oligotrophic water (less favorable for plant growth), but the potential for plant breakage or dislodgment is low due to the calm seas in this region. Using reciprocal transplant experiments, we examined the potential adaptive value of the morphologies of both populations (northern and southern) in the light of these physical gradients among sites north and south of PC, and the tradeoff between rapid growth and increased risk of breakage. We reciprocally transplanted northern-and southern-form E. menziesii among several sites north and south of PC and monitored size and survival of each individual over a 5 mo period. In general, both survival and growth of the northern form was greatest at the northern sites, and southern form survival and growth was greatest at the southern sites. Overall, growth was greatest at the northern sites, and the greatest increase in size was achieved by a southern-form individual at a northern site. These results indicate that regionally specific morphological forms of E. menziesii seem to be uniquely adapted to maximize growth and survival under conditions typical of their native region. However, in the absence of breakage, southern-form E. menziesii have the potential to grow large under northern conditions. Northern-form E. menziesii have a reduced probability of breakage or dislodgment due to their high-strength, low-drag morphology. Southern-form E. menziesii have much lower breaking strengths and higher drag than northern forms, but have a higher surface area per unit of stipe, potentially advantageous for nutrient uptake in the low-nutrient environment south of Point Conception. Although these morphological forms appear to be advantageous within each of these regions, it remains to be explored whether their morphology can be altered at an early life stage or whether it is genetically fixed.