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Examining the Effects of Wavelength and Light Intensity on Astaxanthin Production in Haematococcus lacustris
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2026-01
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Maryam Abdulla_OGS Approved Thesis.pdf
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- Embargoed until 2028-01-31
Abstract
This thesis studies the effects of light quality and light wavelength on growth performance, nutrient uptake, and pigment accumulation of the freshwater microalga Haematococcus lacustris under mixed nutrient and salinity stresses. The research highlights the potential of microalgae as renewable and sustainable biological resources against the background of global concerns associated with the rapid pace of industrialization, population growth, and urbanization that collectively increase stress on natural ecosystems. Due to their high photosynthetic efficiency, fast growth rates, and ability to acclimate to varying conditions, microalgae are a potentially suitable source of sustainable biomass and value-added metabolite generation. The process optimization of culture conditions for biomass and astaxanthin production under operational and environmental constraints at large-scale cultivation sites in arid circumstances like Qatar is the main emphasis of this work.
The experiments were conducted under controlled light conditions (Red, Blue, Red–Blue, and shifting the light from Blue→Red) with known nitrogen and phosphorus levels and increasing salinities. Growth was estimated using an optical density (OD₇₅₀), specific growth rate (μ), and total pigment analysis, while nutrient assimilation, in particular total nitrogen and total phosphorus, was measured to determine shifts in redox metabolism under different light quality spectra and stress conditions.
The findings indicated that the light spectrum and order had noticeably affected the growth kinetics as well as the nutrient removal rate. Highest biomass production and P-use efficiency were supported by blue and red light alone or their combination (Red–Blue), while sequential Blue→Red treatment led to low nutrient assimilation and metabolic shift toward increased carotenoid (astaxanthin) accumulation. Nitrogen and phosphorus uptake significantly decreased under salinity stress, indicating a physiological tradeoff between stress tolerance and nutrient assimilation capacity.
When combined, the findings show that stress and light quality can work together to promote photosynthetic competence and balance the generation of secondary metabolites with vegetative growth. When compared to culture in autotrophic or red+warm light, cultivation of H. lacustris with green+cool/warm spectrum combined with moderate nutrient supply results in higher biomass production and nutrient uptake, whilst sequential or stress-inducing irradiation conditions lead to astaxanthin accumulation at the expense of growth. Therefore, this study provides scientific justification for the development of ideal two-stage cultivation regimes tailored to Qatar's climate, which may align with more general national strategic goals on bioeconomic and environmental sustainability, with an emphasis on value-added products from microalgae.