Temperature, Nitrogen, and Carbon Constraints on Growth and Metabolism of Regional Microalgae Strains

The rapid rise in atmospheric CO2 necessitates strategies for mitigation and valorization. Microalgae offer potential through simultaneous CO2 capture and production of high-value biomolecules. Five Chlorophyta strains (A–E: Micractinium sp., Chlamydomonas sp., Micractinium sp., Chlorococcum sp., and Chlorella vulgaris) were isolated from temperate waters and soils and tested for growth and biochemical responses under controlled nitrogen availability (low: 0.346 g L−1 nitrate; high: 0.6 g L−1 nitrate + ammonia), carbon supply (low: 0.04% CO2; high: 4% CO2), and cultivation systems (batch reactors, fermenters, and varied illumination). Over 14 days, maximum dry biomass was achieved in batch cultivation with CO2 sparging, low nitrogen, and continuous light, ranging from 1.47 g L−1 (strain A) to 2.67 g L−1 (strain D). Biomass composition varied: proteins, 25–45%; carbohydrates, 20–35%; and lipids, 18–28%. Nitrogen limitation promoted lipid accumulation (e.g., strain D: +40%) with concurrent protein decline (−25%). Chlorophyll a/b displayed strain-specific plasticity; high CO2 generally increased chlorophyll, while nitrogen stress reduced it up to 50%. Overall, this study demonstrates that locally adapted Chlorophyta strains can achieve high biomass productivity under CO2 enrichment while allowing for flexible redirection of carbon flux toward lipids, carbohydrates, or pigments through nutrient management. Among the tested isolates, strains D and E emerged as the most promising candidates for integrated CO2 sequestration and biomass production, while strains B, C, and D showed strong potential for biodiesel feedstock; strain A for carbohydrate valorization; and strain E for chlorophyll extraction. Future research should focus on scale-up validation in pilot photobioreactors under continuous operation, optimization of two-stage cultivation strategies for lipid production, integration with industrial CO2 point sources, and strain improvement using modern genomics-assisted breeding and genome-editing technologies. These efforts will support the translation of regional microalgal resources into scalable carbon-capture and bioproduct platforms.