Effects of the Herbicide Diuron on Cordgrass (<Emphasis Type="Italic">Spartina foliosa</Emphasis>) Reflectance and Photosynthetic Parameters |
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Authors: | Susan L Williams Albert Carranza Jennifer Kunzelman Seema Datta Kathryn M Kuivila |
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Institution: | (1) Bodega Marine Laboratory, University of California at Davis, PO Box 247, Bodega Bay, CA 94923-0247, USA;(2) Present address: Fish and Wildlife Research Institute, 100 Eighth Ave SE, St. Petersburg, FL 33701-5095, USA;(3) Civil and Environmental Engineering, University of California at Davis, Davis, CA 95616, USA;(4) Present address: Genome Center, University of California at Davis, Davis, CA 95616, USA;(5) US Geological Survey, California Water Science Center, Sacramento, CA 95819-6129, USA |
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Abstract: | Early indicators of salt marsh plant stress are needed to detect stress before it is manifested as changes in biomass and
coverage. We explored a variety of leaf-level spectral reflectance and fluorescence variables as indicators of stress in response
to the herbicide diuron. Diuron, a Photosystem II inhibitor, is heavily used in areas adjacent to estuaries, but its ecological
effects are just beginning to be recognized. In a greenhouse experiment, we exposed Spartina foliosa, the native cordgrass in California salt marshes, to two levels of diuron. After plant exposure to diuron for 28 days, all
spectral reflectance indices and virtually all fluorescence parameters indicated reduced pigment and photosynthetic function,
verified as reduced CO2 assimilation. Diuron exposure was not evident, however, in plant morphometry, indicating that reflectance and fluorescence
were effective indicators of sub-lethal diuron exposure. Several indices (spectral reflectance index ARI and fluorescence
parameters EQY, Fo, and maximum rETR) were sensitive to diuron concentration. In field trials, most of the indices as well
as biomass, % cover, and canopy height varied predictably and significantly across a pesticide gradient. In the field, ARI
and Fo regressed most significantly and strongly with pesticide levels. The responses of ARI and Fo in both the laboratory
and the field make these indices promising as sensitive, rapid, non-destructive indicators of responses of S. foliosa to herbicides in the field. These techniques are employed in remote sensing and could potentially provide a link between
landscapes of stressed vegetation and the causative stressor(s), which is crucial for effective regulation of pollution. |
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