Biodegradation of linuron in a Phaseolus bioassay detected by chlorophyll fluorescence

Measuring chlorophyll fluorescence of sensitive indicator plants is a promising approach to follow microbial degradation of the photosystem II (PSII) inhibiting herbicide linuron in a plant-microbial bioassay. Both pulse amplitude modulation (PAM) fluorimetry and a stroboscope-based Chla fluorescence imaging system were used to monitor the phytotoxic effect of linuron applied to bean (Phaseolus vulgaris) plants. Inoculation of a hydroponic model system with a linuron-degrading microbial consortium mostly neutralized the phytotoxic effect of the linuron, applied at 0.1 mg l(-1) and 1 mg l(-1). This indicated that the inoculum was even able to degrade linuron at substrate concentrations (0.1 mg l(-1)) that were not detectable by HPLC analysis. The bioprotective effect of the inoculum was also demonstrated when 5 mg l(-1) of linuron was spiked into a soil substrate. This is the first report on the use of chlorophyll fluorescence to demonstrate biodegradation. This method is particularly suited for the detection of low linuron concentrations and could probably also be used for other xenobiotics interfering with photosynthesis. (C) New Phytologist (2002) 154: 821-829.