WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2022 61 ( C O N T I N U E D O N P A G E 6 2 ) shoot weight, flower weight and above-ground plant biomass were measured. Vegetative growth was indicated by shoot height and weight and flowering was indicated by flower count and weight. Yield was measured as above-ground biomass at harvest. All plants were then oven dried at 60 C for 72 hours to determine plant dry weight. Marigold plants treated with one of the four aquaculture effluent treatments without additional fertilization all grew better than the plants irrigated with only distilled water (Table 2). There were no differences among the four treatments in shoot weight, shoot height, flower weight or flower count. However, plants treated with the mineralized aquaculture water did not grow as well as plants in the other three treatments, although they produced the same number of flowers per plant. There was a significant increase in all plant growth and flowering parameters when fertilizer was added to the plants (Table 1). Plants in treatments T5, T6, T7, T8 and T9 had greater shoot weight, flower count and weight and total above-ground weight than plants in treatments DW, T1, T2, T3, and T4. However, there were no differences observed among plants in all treatments that were supplemented with commercial fertilizer. Nevertheless, results suggest that plants in treatments that received only the fertilizer or the fertilizer with the mineralized aquaculture effluent did not perform as well as plants in treatments that received fertilizer coupled with aquaculture water, algae or supernatant water. Discussion In this study, microalgae did not act as plant biostimulants. However, crop growth and flowering were stimulated by nutrients present in aquaculture effluent and freshwater microalgae. Even irrigation with acid-digested aquaculture effluent resulted in improved growth of radish plants compared to controls irrigated with distilled water. However, when plants were fertilized before being treated, algae supplementation did not improve growth. This suggests that the algae or the aquaculture water were improving plant growth because they were supplying nutrients to the plants. Although microalgae are reported to produce a vast array of bioactive compounds (vitamins, amino acids auxin etc.) in their cellular extracts and growth media (Stirk et al. 2002, Stirk et al. 2013, Tarakhovskaya et al. 2007), these compounds did not seem available for uptake by terrestrial plants. Moreover, although the effects of mineralized microalgae were not significantly different from those of other treatments, they tended to be less potent in inducing both plant growth and flower production. Microalgae are composed of macro- and micronutrients necessary for plant growth (Grobbelaar 2013) and thus one would be tempted to assume that non-acid treated samples were inducing better plant growth because of growth factors. However, hot sulfuric acid digestion might have caused the volatilization of some nitrogen compounds and converted phosphorus in the samples into phosphoric acid. The phosphoric acid mixed with the Ca(OH)2 would produce Ca3(PO4)2 which is insoluble and not available for uptake by plant roots. Accordingly, we would expect less growth inducement by mineralized aquaculture water and algae as compared to other treatments. Results of this study show that microalgae and aquaculture effluent are a valuable amendment if properly used. Various studies have documented the positive response of crop growth to microalgae and aquaculture effluent as a fertilizer (Song et al. 2005, Thajuddin amd Subramanian 2005, Abdul-Rahman et al. 2011, Garcia-Gonzalez and Sommerfeld 2016). A few companies suggest that microalgae optimize crop growth and development not just as an organic fertilizer but also as a plant biostimulant. This study does not support these claims. When applied to soil, freshwater microalgae in irrigation water promoted crop growth and flowering only as an organic fertilizer. Briefly, our results suggest that aquaculture effluents that contains organic matter, suspended solids, microalgae and nutrients that can negatively impact receiving water bodies (Tookwinas 1996, Boyd and Tucker 2000) could be a resource if used for irrigation. Aquaculture effluent should be used as an environmentally friendly and sustainable source of complete fertilizer for trees and vegetables on farms as well as flowering plants in homes and parks. Notes Ghaith Amro and Hadi Jaafar, Department of Agriculture, American University of Beirut, Beirut, Lebanon Imad P. Saoud, Department of Biology, American University of Beirut, Bliss St., Beirut, Lebanon. E-mail: is08@aub.edu.lb References Abdul-Rahman, S., I.P. Saoud, M.K. Owaied, H. Holail, N. Farajalla, M. Haidar and J. Ghanawi. 2011. Improving water use efficiency in semi-arid regions through integrated aquaculture/ agriculture. Journal of Applied Aquaculture 23(3):212-230. Adam, M.S. 1999. The promotive effect of the cyanobacterium Nostoc muscorum on the growth of some crop plants. Acta Microbiologica Polonica 482:163-171. Borowitzka, M.A. 2013. High-value products frommicroalgae— their development and commercialisation. Journal of Applied Phycology 25:743-756. Boyd, C.E. and C. Tucker. 2000. Rule-making for aquaculture effluents in the US. Global Aquaculture Advocate 3:81-82. Campanella, L., G. Crescentini, P. Avino and A. Moauro. 1998. Determination of macrominerals and trace elements in the alga Spirulina platensis. Analusis 26(5):210-214. Cooper, M.B. and A.G. Smith. 2015. Exploring mutualistic interactions between microalgae and bacteria in the omics age. Current Opinion in Plant Biology 26:147-153. du Jardin, P. 2015. Plant biostimulants: Definition, concept, main categories and regulation. Sciencia Horticulturae 196:3-14. Garcia-Gonzalez, J. and M. Sommerfeld. 2016. Biofertilizer and biostimulant properties of the microalga Acutodesmus dimorphus. Journal of Applied Phycology 28:1051-1061. Gobbelaar, J.U. 2013. Inorganic algal nutrition. Pages 123-133 in: Richmond and Q. Hu, editors. Handbook of Microalgal Culture: Applied Phycology and Biotechnology. JohnWiley and Sons, Ltd., West Sussex, UK. Gupta, A.B. and K. Lata. 1964. Effect of algal growth hormones on the germination of paddy seeds. Hydrobiologia 241:430-434. Kulik, M.M. 1995. The potential for using cyanobacteria (bluegreen algae) and algae in the biological control of plant pathogenic bacteria and fungi. European Journal of Plant Pathology 101(6):585.
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