Use of chlorophyll fluorescence for monitoring biodegradation of low herbicide concentrations

Chlorophyll fluorescence of sensitive indicator plants in a plant-microbial bioassay offers a promising approach to follow biodegradation of Photosystem II inhibiting herbicides. Photosynthesis-inhibiting herbicides (such as linuron, diuron etc.) increase chlorophyll fluorescence by displacing the secondary electron acceptor Q(B) from its binding site, thereby preventing the conversion of absorbed light energy into electrochemical energy. Several fluorescence parameters, such as Ft, Y, Fv/Fm, Fo, qP and qN were useful for monitoring the phytotoxic effect of linuron applied to Phaseolus plants. By inoculation of a hydroponic model system with a linuron-degrading microbial consortium or a Variovorax paradoxus strain, isolated from this consortium, we were able to neutralize the phytotoxic effect of the linuron. Moreover, the inoculum was still able to degrade linuron at substrate concentrations no longer detectable by HPLC.