using the tilting shaker-with Laminaria digitata as experimental material. The measured respiratory rate was 0.3mgO2g*^h"^ and there was no significant
difference between shaken and unshaken treatments. Photosynthesis
measured concurrently, using the oxygen technique, showed a 2-fold enhancement
when shaken.
4. The effect of current velocity on measured photosynthetic rate ( method)
In order to quantify to some extent the effect of water movement in
a way not possible by shaking experiments, the effects of incubating tissue
1
CN.
Flow rate (cm s )
Figure 3.2. Effec’, of water flow velocity upon photosynthesis in Porphyra
U u'er fluorescent ]ight source (curve fitted by eye), also:. A , photosynthesis
fI' ceho-itions under tungster ight source; P, photosynthesis in shehsr ccn'.r .as \?r tungsten light source; C, r ..otosprrc'-.esis in shaken
T9
were conducted in May using the continuous flow apparatus and fluorescent
light source described in Chapter 2. Samples of Porphyra of dimensions 6 X 0.75 cm (4.5 cm%) were incubated for 2.5 h at 13®C, In each experiment at least two replicate pieces of tissue were incubated at each current
velocity. It was not possible to replicate current velocities exactly in
each experiment. The results are plotted in Figure 3.2. Mean values and
standard errors were calculated for each "block" of results at current
velocities of 0, 0.83, 1.61 and 3.74 cm s" 1. These mean values are
significantly different and form a curve indicating that there is an enhancing effect of current velocity upon photosynthetic rate which is close to a maximum at 4 cm s"l. The rate at this velocity is approximately
two and a half times the static rate.
These experiments were carried out before the saturation intensity
of Porphyra was ascertained (chapter 7), it is possible therefore that the
low irradiance employed here (1.6 mWcm"^ ) was limiting the photosynthetic rate at the higher current velocities. The rates at zero and maximum flow
respectively are both below their shaken and unshaken counterparts in the
tungsten light source experiment (irradiance 15 mWcm^ , see Table 3.1 for
rates) as shown by A and B in Figure 3.2. This means that the "saturation
velocity" of 1 - 2 cm s'^ may be determined in the flow experiments by irradiance, and if irradiance were increased, a different relationship might develop between static and flow conditions.
The only other experiment performed using this fluorescent light
source was done on Porphyra discs of area 4 cm^ incubated in open vessels
(using ^^C) shaken gently by an oscillating-table (4 to 5 times per rain). The'incubation was carried-out in June at 15° C for 3 h. The mean photo- synthetic rate of nine discs in three separate vessels was 5.25 ± 0,48 ligCcm^
0.3 - -o .B 0.3 E 0.3 O n 0.3 (fL. D 0.1 ^ 0 .2 rrg dry waght 0.3 —1— 10 gi
riaure 3.3. Relationship between measured rate of respiration and the ratio tissue-mass ; incubation volume. A, Dumontia 7°C, r ^ = -0»59; B, D i ^ e a,
, ?.5h, ryy = -0.92; C, Laurencia. 9^C, Th, r%y = -0.65; D, Porphyra, 7O0 ,
- -0.(4 . Experiments conducted in laboratory in December under static
Pcalee on abscissa show mg dry weight per 2 8ml bottle and g dry '%on
80
which is shown at C in Figure 3.2. The effect of this gentle shaking is intermediate between the rates attained at zero and maximum flow and confirm that rates are indeed lower with this light source than the tungsten-iodide one.
5. The effect of the ratio of tissue-mass ; incubation volume on the
measured rate of respiration and photosynthesis (oxygen method)
Depletion in experimental vessels and in the sea is a function of the ratio between mass of metabolising organic matter and the volume of
medium available for uptake. Five experiments were conducted using
Laurencia, Dilsea, Dumontia and Porphyra. The incubation volume was maintained
constant, using 28 ml incubation bottles, and varying amounts of algal
tissue were selected by eye to cover a range from less than 0,01 to greater