130
O. Pulz and K. Seheibenbogen
below 30 laEm-2s -1 and reaches maximum growth only at 130 HEm-2s -1.
Richardson generally predicts good growth of diatoms, dinoflagellates and
cyanobacteria at low quantum flux densities, while green algae clearly belong to
the high light intensity group, for some Chlorella strains optimum radiation
intensities of not below 300 ~tE m- 2 s- 1 being recorded. In the data collection
Richardson has respected the light/dark cycle (15/9 h), because at continuous
illumination some varieties will change the original growth behaviour [39].
That means that the range of photosynthetically relevant radiation intensities at
permanent light is generally even more restricted.
3.4 Effects of Changing Light Conditions on Algal Growth
Algae are able to adapt to significantly higher radiation intensities for a
short period. The midday sun emits radiation densities of more than
2000 ~tE m- 2 s- ~ PAR. In dynamic cultures, the radiation load is compensated
for by reflection and absorption as well as by mixing effects [40]. Grobbelaar
[41] observed an increase of productivity at high turbulences and suggested
a possible synergistic relation between the light/dark cycle in the seconds-range
and mechanisms of material transport. Laws [42] has cited seven publications in
which an increased rate of photosynthesis at flash-light is described. He and his
coworkers [43] have developed a simple device for the generation of highly
turbulent fluxes where algal cells are exposed to the ambient light at a frequency
of 60 Hz; the production rate of the alga Phaeodaetylum was almost doubled.
This corresponds to the flash-light effect postulated as growth promoter by
Warburg as early as 1919 [44] and later by Kok [45]. Terry [46] has calculated
an increase of the photosynthetic efficiency at a low frequency. Weller and
Frank [47] and Phillips and Myers [48], however, did not establish any increase
of the rate of photosynthesis, which was rather significantly lower at low
frequencies and approached the continous light course only at higher flash-light
rates. Recent work with LEDs as pulsed light sources in the range 0.1-100 Hz
have confirmed this course. In this connection, Grobbelaar and Neddal [49]
mention that it became apparent that algae would not acclimatize to certain
frequencies, as theory of electron transport mechanism suggested. However,
using the same intermittant light regime will result in growth rates higher and
photoinhibition rates lower than in equivalent continuous light in some strains
of Chlorophyceae [50]. As a result of the analysis of several references, Giger
and Sager [51] support the hypothesis of Rabinowitch [52] that enzymes of
photosynthesis are limited in concentration only because of their size to a maximum of 1 per 300 chlorophyll molecules; as a consequence the maximum
productivity rate of light-collecting pigments inevitably will be higher than that
of the subsequent enzyme reactions. The quantum utilization at intermittant
light will thus not be improved. According to an extensive theory [-53], the cyclic
excitation of arbitrary reactions will lead to an increase of productivity rates by
a maximum of 10-20%. Finally, the question for the flash-light effect now as
O. Pulz and K. Seheibenbogen
below 30 laEm-2s -1 and reaches maximum growth only at 130 HEm-2s -1.
Richardson generally predicts good growth of diatoms, dinoflagellates and
cyanobacteria at low quantum flux densities, while green algae clearly belong to
the high light intensity group, for some Chlorella strains optimum radiation
intensities of not below 300 ~tE m- 2 s- 1 being recorded. In the data collection
Richardson has respected the light/dark cycle (15/9 h), because at continuous
illumination some varieties will change the original growth behaviour [39].
That means that the range of photosynthetically relevant radiation intensities at
permanent light is generally even more restricted.
3.4 Effects of Changing Light Conditions on Algal Growth
Algae are able to adapt to significantly higher radiation intensities for a
short period. The midday sun emits radiation densities of more than
2000 ~tE m- 2 s- ~ PAR. In dynamic cultures, the radiation load is compensated
for by reflection and absorption as well as by mixing effects [40]. Grobbelaar
[41] observed an increase of productivity at high turbulences and suggested
a possible synergistic relation between the light/dark cycle in the seconds-range
and mechanisms of material transport. Laws [42] has cited seven publications in
which an increased rate of photosynthesis at flash-light is described. He and his
coworkers [43] have developed a simple device for the generation of highly
turbulent fluxes where algal cells are exposed to the ambient light at a frequency
of 60 Hz; the production rate of the alga Phaeodaetylum was almost doubled.
This corresponds to the flash-light effect postulated as growth promoter by
Warburg as early as 1919 [44] and later by Kok [45]. Terry [46] has calculated
an increase of the photosynthetic efficiency at a low frequency. Weller and
Frank [47] and Phillips and Myers [48], however, did not establish any increase
of the rate of photosynthesis, which was rather significantly lower at low
frequencies and approached the continous light course only at higher flash-light
rates. Recent work with LEDs as pulsed light sources in the range 0.1-100 Hz
have confirmed this course. In this connection, Grobbelaar and Neddal [49]
mention that it became apparent that algae would not acclimatize to certain
frequencies, as theory of electron transport mechanism suggested. However,
using the same intermittant light regime will result in growth rates higher and
photoinhibition rates lower than in equivalent continuous light in some strains
of Chlorophyceae [50]. As a result of the analysis of several references, Giger
and Sager [51] support the hypothesis of Rabinowitch [52] that enzymes of
photosynthesis are limited in concentration only because of their size to a maximum of 1 per 300 chlorophyll molecules; as a consequence the maximum
productivity rate of light-collecting pigments inevitably will be higher than that
of the subsequent enzyme reactions. The quantum utilization at intermittant
light will thus not be improved. According to an extensive theory [-53], the cyclic
excitation of arbitrary reactions will lead to an increase of productivity rates by
a maximum of 10-20%. Finally, the question for the flash-light effect now as