Photosynthetic acclimation to different light levels in the brown marine macroalga, <Emphasis Type="Italic">Hizikia fusiformis</Emphasis> (Sargassaceae,Phaeophyta) |
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Authors: | Dinghui Zou Kunshan Gao |
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Institution: | (1) The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Chinese Ministry of Education, College of Environmental Science and Engineering, South China University of Technology, Guangzhou, 510006, China;(2) State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, 361005, China |
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Abstract: | Hizikia fusiformis thalli experience dynamic incident light conditions during the period of growth. The present study was designed to examine
how changing photon irradiance affects the photosynthesis both in the short and long terms by culturing H. fusiformis under three different light levels: 35 μmol photons m-2 s-1 (low light, LL), 85 μmol photons m-2 s-1 (intermediate light, IL), and 165 μmol photons m-2 s-1 (high light, HL). A similar relative growth rate was observed between IL- and HL-grown algae, but the growth rate was significantly
reduced in LL-grown algae. The photosynthetic rates (P
n) measured at their respective growth light levels were found to be lowest in the thalli grown at LL and highest at HL. However,
LL-grown algae exhibited much higher P
n in comparison with IL- and the HL-grown thalli at the same measuring photosynthetic photon flux density, indicating the photosynthetic
acclimation to low growth light in H. fusiformis. The photosynthesis–light curves showed that LL-grown algae had a highest light-saturating maximum P
n (P
max) in comparison with IL- or HL-grown algae when the photosynthetic rates were expressed on the biomass basis. However, P
max was highest in HL-grown algae compared to IL- or LL-grown algae when the rates were normalized to chlorophyll a. The photosynthesis–inorganic carbon (Ci) response curves were also significantly affected by the growth light conditions.
The highest value of apparent photosynthetic conductance occurred in LL-grown algae while the lowest value in HL-grown algae.
Additionally, the activity of external carbonic anhydrase (CA) tended to increase while the total CA activity inclined to
decrease in H. fusiformis thalli when the growth light level altered from 35 to 165 μmol photons per square meter per second. The external CA inhibitors
showed a higher inhibition in HL-grown algae compared with LL-grown algae. It was proposed that photosynthetic acclimation
to low light condition in H. fusiformis was achieved through an increase in the number of reaction centers and increased capacities of electron transport and of
Ci transport within cells. The ability of photosynthetic acclimation to low light confers H. fusiformis thalli to overcome the environmental low light condition as a result of the attenuation of seawater or self-shading through
enhancing its photosynthetic performance and carbon assimilation necessary for growth. |
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