Results (
Thai) 2:
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A previous study reported similar results in Chlorella and Cyclotella
(Jøsrgensen, 1969). The Chlorella adapted to a new light intensity
mainly by changing its pigment contents. Therefore, the cells
exposed to intense light intensities had a lower chlorophyll content
than cells exposed to low light intensities. The chlorophyll
content in Cyclotella was the same at low or high light intensities.
However, the biomass photosynthesis was considerably higher for
cells grown at higher light intensities (Jøsrgensen, 1969), and the
carotenoid content was higher under a stronger light intensity in
microalgae (Campenni et al., 2013).
Changes in the ratio of bacteriochlorophyll and carotenoid in
PSB were also studied. As Table 1D shows, within light intensities
of 500–4000 lux the carotenoid/bacteriochlorophyll ratio
decreased gradually with time. Only at 8000 lux, the carotenoid/
bacteriochlorophyll ratio increased gradually with time and
reached 2.23 after 120 h. It revealed that the effects of light intensity
on carotenoid/bacteriochlorophyll ratio in PSB were different.
At 8000 lux, the carotenoid/bacteriochlorophyll ratio was the
highest. It meant that the carotenoid were higher or that the bacteriochlorophyll
were lower than other groups. It could be
explained by the fact that the light stimulated photo-protection
by the carotenoid and reduced the number of bacteriochlorophyll
in their excited states. In fact, at intense light intensities, energy
was absorbed by PSB light harvesting complex, which dissipated
as heat before it reaches the reaction center. An 80% of the total
absorbed energy dissipated as heat (Li et al., 2009). Meanwhile,
the amount of bacteriochlorophyll in their excited states reduced.
The higher the bacteriochlorophyll and carotenoid secreted than
other light intensities group, the lower the light conversion efficiency
turned out to be.
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