Evaluation of selenium-enriched microalgae produced on domestic wastewater as biostimulant and biofertilizer for growth of selenium-enriched crops

This study assessed selenium (Se)-enriched microalgae biomass produced in a pilot-scale raceway pond treating domestic wastewater and an extract thereof as biostimulant and biofertilizer. After producing the Se-enriched microalgae in a raceway pond treating domestic wastewater, the effect of Se-enriched microalgae biomass and an extract thereof on seed germination, growth, and yield of beans (Phaseolus vulgaris L.) was studied by conducting a germination test and foliar and soil applications in pot experiments. Furthermore, the potential of the Se-enriched microalgae dry biomass and extract to elevate the Se concentration of beans, leading to a biofortified crop, was also assessed in a pot experiment. Presoaking seeds in the Se-enriched microalgae extract at low concentration (1%) enhanced their germination, as measured by the significant increase of seedling length and vigor index. Application of the Se-enriched microalgae extract as foliar spray was more effective in stimulating the growth of beans and increasing the Se concentration in the seeds compared to its application as soil drench. Foliar spray resulted in a 3.5 times increase of the dry biomass of the seeds (at 1%) and 1.8 times Se increment in the seeds (at 5%). Additionally, amendment of the soil with Se-enriched microalgae biomass (at 5%) enhanced the growth of beans (3.2 times for seeds) and Se concentration in the bean plants (1.8 times for seeds), simultaneously. These results indicate that microalgae cultivated in Se-rich wastewater could be used as a microalgae-based biofertilizer or biostimulant to improve the bean seed yield and the Se content in the beans, leading to beans with a higher market value. This may also offer an environmental-friendly and sustainable approach to biofortify food crops in Se-deficient regions.