ABSTRACT: Nitrifying bacteria (NH₄⁺ and NO₂^- oxidizers) are capable of recovery from photoinhibition in the dark. After short-term (2 to 4 h) irradiations, significant differences were found between the 2 groups. NH₄⁺ 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^-2) or sunlight (360 to 400 W m^-2). In contrast, NO₂^- oxidizers only failed to recuperate activity after sunlight and near-UV (300 to 375 nm) treatment. Artificial light (5 to 25 W m^-2) did not affect nitrite oxidation. Thus, recovery of NH₄⁺ 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.

KEY WORDS: Recovery · Nitrification · Nitrifying bacteria

Published in MEPS Vol. 141 (1996) on October 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996