## 3 Results  
### Assessment of the Light and Temperature Fluctuations on the Algae Growth  
Well-controlled light and temperature cycles, alone and then in combination, were used to investigate their respective effects on \(N\). sp. _QUI130_. Different behaviors were observed, as shown in Figures 4 and 5. When the day/night cycle stress (Regime C) was applied to a steady-state culture obtained at constant continuous light and temperature, an immediate and sharp 50% decrease in algae biomass was observed, varying between 1.9 kg.m\({}^{-3}\) and 0.96 kg.m\({}^{-3}\) (Figure 4A). This decrease was higher than that reported by [7] and [6], who observed a reduction of almost 30% in algae biomass after moving from a continuous light regime to a day/night cycle regime. \(N\). sp. _QUI130_ acclimated to the day/night cycle after five days, and an almost constant biomass concentration was achieved over time. Measurements over the 24 h cycle were then conducted (Figure 5A). There was a 15% increase in biomass concentration with light intensity increasing from 1.3 at dawn to 1.5 kg.m\({}^{-3}\) at the maximum daytime irradiance. It reached a maximum of 1.65 kg.m\({}^{-3}\) at the end of the day after 14 h of illumination, with a total 25% increase in biomass concentration (Figure 5A). These results concur with [PERSON] and [PERSON] and [PERSON] et al., who demonstrated a significant increase in algae biomass concentration in response to an increase in light [5; 26]. However, a 15% reduction in biomass concentration was observed during the night period, from 1.5 kg.m\({}^{-3}\) to 1.3 kg.m\({}^{-3}\). A similar observation was reported by [PERSON] et al. in their work on _Parachlorella kessleri_ cultivated in simulated day/night cycles representing solar conditions in Nantes, France [27]. The average biomass concentration generated by all the samples was 1.4 kg.m\({}^{-3}\) and the volumetric biomass productivity under day/night cycle (Regime C) was 0.67 kg.m\({}^{-3}\) day\({}^{-1}\) (corresponding to an areal biomass productivity of 20.1 g.m\({}^{-2}\).day\({}^{-1}\)). Figure 4: Time acclimation of \(N\). sp. QU130 under three different cultivation cycles stresses, **(A)**: Cultivation under day/night cycles (Experiment C); **(B)**: Cultivation under temperature fluctuation (Experiment B) and **(C)**: Cultivation under combined light and temperature cycles (Experiment D). The culture exhibited very different behavior when temperature cycle stress was applied to the steady-state culture under constant PFD and T (Regime B). A slight 15% decrease in \(N\). sp. QU130 productivity was first observed, followed by a quick recovery of the algae strain growth, indicating a rapid acclimation to temperature after five days (Figure 4B). The short exposure (8 h) of the culture to a high temperature boosted the growth performance of the strain by enhancing its physiological and biochemical properties; an increase of almost 50% in biomass concentration was recorded after acclimation to temperature cycles at 2.4 kg.m\({}^{-3}\), compared to a biomass concentration of 1.75 kg.m\({}^{-3}\) under constant PFD and T conditions. The situation was different for [PERSON] and [PERSON], who reported that an increase to more than the optimal temperature for growth was generally associated with cell damage or cell death [28]. This has been explained by heat stress,  
Figure 5: Evolution of biomass concentration of \(N\). sp. QU130 under three different cultivation regimes: (**A**): Cultivation under day/night cycles (Experiment C); (**B**): Cultivation under temperature fluctuation (Experiment B) and (**C**): Cultivation under combined light and temperature cultivation (Experiment D). Measurements taken in triplicates on 3 different days in the steady-state culture (only Trial 1 is shown in Figure 5c—similar results for other trials). which abolishes the enzymatic activities or modifies the structure and activity of proteins and membrane fluidity, leading to disturbance of the metabolic processes and ultimately reducing algae growth [29; 30; 31].