Breaking the growth-light trade-off in microalgae: toward efficient phototrophic bioproduction via a...

The "Growth-Light Trade-off" in microalgae between high specific growth rate and high light use efficiency (LUE) presents a key barrier to its industrialization. To overcome this, a physiological-response-guided step-gradient light-downgrading strategy was developed based on two operational thresholds identified in this study: a "safe high-light window" for rapid energy storage and a "photodamage threshold" beyond which severe oxygen-stress-associated damage becomes evident. The safe window was first leveraged under high incident light intensity (I₀, e.g., 600 μmol m^-2 s^-1), where enhanced photosynthetic activity drove rapid cell enlargement for energy storage while the dissolved oxygen concentration in the culture medium ([DO]) remained below a critical hyperoxic level (∼24.5 mg L^-1). I₀ was then proactively stepped down (e.g., to 300 then 100 μmol m^-2 s^-1) before the culture reached the "photodamage threshold", characterized by [DO] peaking at ∼ 37.1 mg L^-1 and pronounced physiological deterioration, thereby avoiding the severe damage observed under static high-I₀ cultivation. By dynamically matching I₀ to leverage the high-light-induced physiological advantage for low-light growth, this strategy broke the trade-off, enhancing the average specific growth rate of biomass (μ¯) by 63.06% and LUE by 29.63% while balancing energy input against oxygen-stress risk. This work establishes a physiology-guided operational framework for intelligent, adaptive microalgal cultivation.