IOSR Journal of Environmental Science, Toxicology and Food Technology (IOSR-JESTFT) e-ISSN: 2319-2402,p- ISSN: 2319-2399.Volume 14, Issue 8 Ser. III (August 2020), PP 47-55 www.iosrjournals.org DOI: 10.9790/2402-1408034755 www.iosrjournals.org 47 | Page Comparative analysis of the response of three macrophytes under different ammonium concentrations: insights into the role of growth forms. Annah Timinah Nasimiyu 1,2 , Wyckliffe Ayoma Ochieng 1,2 &Cornelius M. Kyalo 2 1 Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, Hubei, P.R China. 2 University of Chinese Academy of Sciences, 100049, Beijing, PR China. Abstract: Background:Ammonium (NH 4 + ) is an inorganic form of nitrogen that is necessary for the growth and development of aquatic plants. However, NH 4 + is toxic when its concentrations exceed plant requirement and the extent of its toxicity is poorly understood. Materials and Methods: This study sought to compare the responses of three macrophytes (Ceratophyllum demersum, Vallisneria natans, and Potamogeton maackianus) to varying NH 4 + concentrations with respect to their varying growth forms, under four different Ammonium (NH 4 + ) concentrations (control – 0mg/L, low – 0.1mg/L, medium – 15mg/L and high – 50mg/L). Ammonium stress was assessed using the parameters; Chlorophyll a and b, Protein content, Chlorophyll fluorescence (Fv/Fm), Free amino acids (FAA), and Soluble sugars. Results: It was observed that FAA and Protein content increased significantly (P<0.05) with increased Ammonium concentrations regardless of the species. However, both Chlorophyll content and Soluble sugars exhibited a general decrease with increased NH 4 + concentrations, except for C. demersum in which the Chlorophyll content increased. Generally, there were varied responses of macrophytes to elevated ammonium concentrations aligned with growth forms, with the canopy-forming P. maackianus and rootless C. demersum exhibiting significant tolerance while the rosette-forming V. natans was sensitive. This is attributed to differences in their ability to intercept light whereby the rosette-forming V. natans is short and prone to low light conditions which lead to insufficient carbohydrates production, a requirement to detoxify ammonium toxicity. Conclusion: In conclusion, P. maackianus and C. demersum may feasibly be preferred in the practical restoration of shallow aquatic ecosystems experiencing high NH 4 + toxicity. Key Words: Ammonium toxicity, Growth forms, Macrophytes, Phytoremediation, Restoration. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 12-08-2020 Date of Acceptance: 28-08-2020 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction Macrophytes are large aquatic plants that are categorized into four primary life forms (emergent, submerged, floating and free-floating) (Chambers et al. 2008)and are essential in aquatic ecosystems in providing habitats for fish, aquatic invertebrates and birds (Dvoiaki et al. 1982, Martin and Valentine 2012). Studying aquatic macrophytes is vital in understanding the ecological status of aquatic ecosystems, including the characterization of water quality (Ghavzan et al. 2006). Therefore, macrophytes have increasingly attracted research attention, specifically based on their ability to sequestrate many pollutants and provide aeration services in contaminated water bodies (Boyd 1970). Unlike conventional clean-up techniques, macrophytes perform natural phytoremediation processes within aquatic systems in a cost-effective and environmentally sustainable manner (Shah et al. 2014). This is due to their fast growth which translates to huge biomass, the capability to accumulate large amounts of diverse pollutants in nature, easier and rapid propagation, and abundant root system that increases surface area for absorption of contaminants (Jahnke et al. 1991, Tripathi and Shukla 1991). Despite the important role played by macrophytes, they are declining globally due to exposure to high eutrophication in aquatic systems. Eutrophication is largely attributed to the presence of excessive macro- nutrients, primarily nitrogen and phosphorus (O'Hare et al. 2018), in water bodies.Nitrogen is a vital nutrient for plant growth and yield (Miller and Cramer 2005), including the provision of building blocks for the synthesis of biomolecules such as proteins and nucleic acids (Masclaux-Daubresse et al. 2010).In addition to being a