Factors governing the germination of Chara vulgaris L. and Nitella flexilis L. were investigated in a series of three experiments. Temperature, light regimes, drying, and changes in oxidation-reduction potential are postulated to be possible triggers working in isolation or in combination on dormant oospores originating in sediments with different physical/chemical characteristics. In Experiment 1, none of the N. flexilis oospores inoculated into Petri plates and culture tubes containing either agar or water and then exposed to 'normal' 12 h daylight 12 h dark germinated when the redox of the media remained relatively constant over the 20-day observation period, while all of the oospores in a tube in which the redox of the agar declined to below 200 mV, germinated. Similarly no germination occurred in the dark without a decrease in redox. When redox fell to below 200 mV, 11% of the inoculated oospores germinated. In Experiment 2, N. flexilis and C. vulgaris oospores were subjected to cold pre-treatments and inoculated into either water or agar in both plates and tubes. Of the N. flexilis oospores 53% germinated in the dark, and 31% under normal lighting. Of the C. vulgaris, 3% germinated in the dark and 53% under normal lighting. The stimulation of germination with the decrease in redox in the media did not re-occur. Experiment 3 compared the germination of C. vulgaris oospores from four ponds contaminated by mining wastes and from a comparatively clean wetland. The oospores were again subjected (or not) to cold pre-treatments, and were drawn from both freshly concentrated sediments and air-dried sediments that had been held in storage for either 97 or 376 days. Notably, a consistent reduction in oospore viability occurred in oospores from a particular mine pond, contaminated by nickel tailings. © 2007 Elsevier B.V. All rights reserved.
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