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.