Detection of ammonia toxicity in microalgae by chlorophyll fluorescence

Abstract

To improve the specificity and accuracy of ammonia detection in Chlorella vulgaris under high temperature, high light, and ammonia stress conditions, fast chlorophyll a fluorescence induction (OJIP) curve was measured using varying saturation pulse intensities and analyzed through multivariable statistical methods. The OJIP curve shapes alone showed limited discriminative power, as the fluorescence signals at the J and I phases were similar across the three stress conditions. Quantitative evaluation using OJIP parameters revealed relatively high correlations between ammonia concentration and specific parameters such as VL and VK (R² = 0.683 and 0.642, respectively). Moreover, the application of multivariable analysis using a broader set of OJIP parameters significantly improved both prediction accuracy and correlation (0.84 and 0.92, respectively). Additionally, the use of different saturation pulse intensities enabled clearer detection of the L- and K-bands, enhancing the reliability of these fluorescence features. These precisely captured parameters contributed to the improved performance of ammonia detection (prediction accuracy and correlation were 0.91 and 0.96). On the other hand, the model generated at different saturation pulse intensity largely misestimated ammonia concentration.