Differential sensitivity of five cyanobacterial strains to ammonium toxicity and its inhibitory mechanism on the photosynthesis of rice-field cyanobacterium Ge–Xian–Mi ( Nostoc)

• Published in: Aquatic toxicology Vol. 89; no. 2; pp. 113 - 121
• Main Authors: Dai, Guozheng, Deblois, Charles P., Liu, Shuwen, Juneau, Philippe, Qiu, Baosheng
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 29.08.2008; Amsterdam; New York: Elsevier Science; Elsevier Science
• Subjects: ammonium chloride; Ammonium Chloride - toxicity; Ammonium toxicity; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; chlorophyll; Cyanobacteria - drug effects; Cyanobacteria - growth & development; Cyanobacteria - metabolism; Cyanobacterium; Ecotoxicology, biological effects of pollution; Electron Transport; Fertilizers - toxicity; fluorescence; Fundamental and applied biological sciences. Psychology; General aspects; Growth; microbial growth; nitrogen fertilizers; nitrogen-fixing cyanobacteria; Nostoc; Nostoc - drug effects; Nostoc - growth & development; Nostoc - metabolism; Oryza - growth & development; Oxygen Consumption - drug effects; Paddy field; Photosynthesis; Photosynthesis - drug effects; physiological response; pigments; Pigments, Biological - biosynthesis; potassium chloride; Species Specificity; strains; toxicity; DCPIP; Growth; Chl a; MV; OEC; F m; Cyanobacterium; PC; σ PSII; APC; PE; TAPS; F 0; DCMU; τ Qa; Nostoc; Paddy field; Ammonium toxicity; Photosynthesis; DCPIPH 2; F v; F v/ F m; Monocotyledones; Ammonium; Ecotoxicology; Toxicity; Aquatic environment; Oryza sativa; Gramineae; Angiospermae; Cyanobacteria; Bacteria; Spermatophyta
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2008.06.007

Effects of two fertilizers, NH 4Cl and KCl, on the growth of the edible cyanobacterium Ge–Xian–Mi ( Nostoc) and four other cyanobacterial strains were compared at pH 8.3 ± 0.2 and 25 °C. Their growth was decreased by at least 65% at 10 mmol L −1 NH 4Cl but no inhibitory effect was observed at the same level of KCl. Meanwhile, the strains exhibited a great variation of sensitivity to NH 4 + toxicity in the order: Ge–Xian–Mi > Anabaena azotica FACHB 118 > Microcystis aeruginosa FACHB 905 > M. aeruginosa FACHB 315 > Synechococcus FACHB 805. The 96-h EC 50 value for relative growth rate with regard to NH 4 + for Ge–Xian–Mi was 1.105 mmol L −1, which was much less than the NH 4 + concentration in many agricultural soils (2–20 mmol L −1). This indicated that the use of ammonium as nitrogen fertilizer was responsible for the reduced resource of Ge–Xian–Mi in the paddy field. After 96 h exposure to 1 mmol L −1 NH 4Cl, the photosynthetic rate, F v/ F m value, saturating irradiance for photosynthesis and PSII activity of Ge–Xian–Mi colonies were remarkably decreased. The chlorophyll synthesis of Ge–Xian–Mi was more sensitive to NH 4 + toxicity than phycobiliproteins. Thus, the functional absorption cross section of Ge–Xian–Mi PSII was increased markedly at NH 4Cl levels ≥1 mmol L −1 and the electron transport on the acceptor side of PSII was significantly accelerated by NH 4Cl addition ≥3 mmol L −1. Dark respiration of Ge–Xian–Mi was significantly increased by 246% and 384% at 5 and 10 mmol L −1 NH 4Cl, respectively. The rapid fluorescence rise kinetics indicated that the oxygen-evolving complex of PSII was the inhibitory site of NH 4 +.