| Abstract |
Heating cost during the night is a problem in outdoor cultivation of a cyanobacterium Arthrospira platensis. Low night temperature causes decreased biomass productivity during daytime and biomass loss during night, but there are few studies to fully investigate these impacts at the same time. To evaluate the effect of dark-period temperature (10–35 °C) on the net productivity (g-DW L−1 d−1) of Arthrospira platensis, semi-continuous cultivations were conducted in 1-L cylindrical glass photobioreactors with an LD cycle of 12-hour light and 12-hour dark under a light-period temperature of 35 °C and dark-period temperatures between 10 and 35 °C. By monitoring at 12-hour intervals, daytime productivity (g-DW L−1 d−1) and night biomass loss (%biomass) were investigated to understand net productivity. There was no significant difference in the net productivity and daytime productivity at high dark-period temperatures (25, 30 and 35 °C). On the other hand, at lower dark-period temperatures (10 and 15 °C), the net productivity and daytime productivity were at most 30% lower than that recorded at higher temperatures (25 and 30 °C). The dark-period temperatures were negatively correlated with carbon to nitrogen (C:N) ratio and positively correlated with dark-respiration rates, which suggested low protein synthesis at low dark-period temperature leading to the low net productivity at 10 and 15 °C. The tolerance of Arthrospira platensis to low dark-period temperature (25 °C) indicates possible cost reduction to control temperature during dark period. This study clarified that the low night temperature reduced net productivity of microalgae and cyanobacteria, and night temperature should be managed in outdoor cultivation based on the permissible dark-period temperature range.
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