Photoinhibition of marine nitrifying bacteria. 11. Dark recovery after monochromatic or polychromatic irradiation

Nitrifying bacteria (NH4+ and NO2oxidizers) are capable of recovery from photoinhibitlon in the dark. After short-term (2 to 4 h) irradiations, significant differences were found between the 2 groups. NH,' oxidizers subjected to longer wavelengths (>400 nm; 25 W m-2) or polychromatic light (15 W m-2) regained activity faster (0.5 to 1 h) than if exposed to shorter wavelengths (<400 nm; 25 W m-') or sunlight (360 to 400 W m"). In contrast, NOzoxidizers only failed to recuperate activity after sunlight and near-UV (300 to 375 nm) treatment. Artificial light (5 to 25 W did not affect nitrite oxidation. Thus, recovery of NH,+ and NO2' oxidizing activities exhibited both dose and wavelength dependencies. These distinct recovery responses imply that nitrogen turnover in aquatic ecosystems depends on a number of factors among which light transmission properties of different water types (i.e. from lakes, rivers, estuaries, coastal marine and oceans) and physiological differences between nitrifying bacteria play significant roles.