title: Effects of monosulfuron on growth, photosynthesis, and nitrogenase activity of three nitrogen-fixing cyanobacteria.
abstract: Application of monosulfuron, a new sulfonylurea herbicide, produced a simulative effect on heterocyst formation and nitrogenase activity but an inhibitory effect on photosynthesis, i.e., a lower net photosynthetic rate, fewer photosynthetic pigments, and a smaller Fv/Fm ratio at increasingly higher monosulfuron concentrations (0.001-10 mg/l) for three nonspecific filamentous nitrogen-fixing cyanobacteria: Anabaena azollae, A. flos-aquae, and A. azotica. The decrease in biliprotein of algal cells was less than that of carotenoid and chlorophyll-a. Monosulfuron was more readily degraded and less accumulated in A. azotica compared with A. azollae and A. flos-aquae. The three algae exhibited varying degrees of sensitivity to monosulfuron: Calculated 50% inhibition concentrations (IC(50)s) of algal growth and no observed-effect concentration (NOEC) values after 4 days of treatment were 0.014 and 0.005, 0.029 and 0.019, and 0.22 and 0.075 mg/l for A. flos-aquae, A. azollae, and A. azotica, respectively. Normal agricultural use of monosulfuron at postemergence rates of 0.3-0.8 mg/l in rice fields will likely be toxic to these three ubiquitous nitrogen-fixing cyanobacteria. Low-dose monosulfuron application (<0.1 mg/l) enables growth of the more tolerant A. azotica as biofertilizer, and the use of photosynthetic efficiency and growth rates as sensitive-indicator indexes of toxicity to nitrogen-fixing cyanobacteria are recommended.
authors.affiliation: Department of Environmental Science and Resources, Shanghai Jiaotong University, China. jyshen88@sjtu.edu.cn
authors.forename: Jianying
authors.initials: J
authors.lastname: Shen
authors.forename: Wei
authors.initials: W
authors.lastname: Luo
mesh_terms: D017033:Anabaena / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism; D046869:Dolichospermum flos-aquae / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D020128:Inhibitory Concentration 50; D009586:Nitrogen Fixation / Q000187:drug effects; D009591:Nitrogenase / Q000187:drug effects* / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D013453:Sulfonylurea Compounds / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D014873:Water Pollutants / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*
chemical_list: D006540:Herbicides; D011743:Pyrimidines; D013453:Sulfonylurea Compounds; D014873:Water Pollutants; C495688:monosulfuron; D009591:Nitrogenase