Light history modulates antioxidant and photosynthetic responses of biofilms to both natural (light) and chemical (herbicides) stressors

Abstract

In multiple stress situations, the co-occurrence of environmental and chemical factors can influence organisms' ability to cope with toxicity. In this context, the influence of light adaptation on the response of freshwater biofilms to sudden light changes or to herbicides exposure was investigated by determining various parameters: diatom community composition, photosynthetic parameters, chlorophyll a content, antioxidant enzyme activities. Biofilms were grown in microcosms under sub-optimal, saturating, and high light intensities and showed already described characteristics of shade/light adaptation (community structure, photosynthetic adaptation, etc.). Light history modulated antioxidant and photosynthetic responses of biofilms to the stress caused by short-term exposure to sudden light changes or to herbicides. First biofilms adapted to sub-optimal light intensity (shade-adapted) were found to be more sensitive to an increase in light intensity than high-light adapted ones to a reduction in light intensity. Second, while light history influenced biofilms' response to glyphosate, it had little influence on biofilms' response to copper and none on its response to oxyfluorfen. Indeed glyphosate exposure led to a stronger decrease in photosynthetic efficiency of shade-adapted biofilms (EC(50) = 11.7 mg L(-1)) than of high-light adapted communities (EC(50) = 35.6 mg L(-1)). Copper exposure led to an activation of ascorbate peroxidase (APX) in biofilms adapted to sub-optimal and saturating light intensity while the protein content decreased in all biofilms exposed to copper. Oxyfluorfen toxicity was independent of light history provoking an increase in APX activity. In conclusion this study showed that both previous exposure to contaminants and physical habitat characteristics might influence community tolerance to disturbances strongly.

Evaluation of Algal Biofilms on Indium Tin Oxide (ITO) for Use in Biophotovoltaic Platforms Based on Photosynthetic Performance

“…One of the most important information is the non-destructive generation of light-response curves of photosynthetic activity [47]. The distance between the optical fiber-optics and the sample surface was set at 2 mm [48]. Eight selected strains starting with the same concentration of pure cultures at OD 620 nm at 0.5.…”

Herbicide toxicity on river biofilms assessed by pulse amplitude modulated (PAM) fluorometry

“…These parameters can also potentially detect effects of compounds acting on targets other than PSII, since chemicals that inhibit any cellular process downstream of PSII (e.g., carbon assimilation or respiration, photosynthetic electron transport) will lead to increased excitation pressure on PSII. Recent investigations on such compounds recommended combining this approach with other parameters (Bonnineau et al, 2012).…”

The influence of reduced light intensity on the response of benthic diatoms to herbicide exposure

“…There were no interactions between light and herbicide effects at the community level at any of the sites. However, adaptations to environmental conditions such as light intensity have been found to alter the sensitivity of periphyton to herbicides resulting in changes in benthic diatom community composition . The ability of individual diatom taxa to adapt to light availability may influence their response to herbicide exposure, especially in the case of photosystem II herbicides, which act directly on photosynthesis .…”

“…However, adaptations to environmental conditions such as light intensity have been Table 2. Classification of diatom taxa as sensitive or tolerant based on responses in rapid toxicity tests to atrazine and glyphosate and occurrence of taxa from counts within control communities at t ¼ 0 (Supplemental Data, found to alter the sensitivity of periphyton to herbicides resulting in changes in benthic diatom community composition [13,18,38]. The ability of individual diatom taxa to adapt to light availability may influence their response to herbicide exposure, especially in the case of photosystem II herbicides, which act directly on photosynthesis [39].…”