Can oospore germination patterns explain charophyte distribution in permanent and temporary wetlands?

The patterns of germination of oospores of several species of charophytes were investigated to explain the distribution of charophytes in permanent and temporary wetlands in north-eastern New South Wales, Australia. Germination from seed banks and after storage was evaluated, Seed banks were pre-treated with combinations of temperature and moisture to simulate the effect of inundation in different seasons, Oospores of five species of Nitella and two species of Chara germinated from the seed banks, Nitella cristata var. ambigua, N. sonderi and N. subtilissima germinated in large numbers and the pattern and timing of emergence of these species was analysed, Nitella cristata var, ambigua, a winter germinating species, had relatively synchronous and early germination from seed banks when exposed to cues for the onset of winter. Nitella sonderi and N. subtilissima displayed extended germination from seed banks of wetlands that have variable water regimes. Drying the seed bank enhanced germination of these three species. Oospores collected from plants of four species were subject to different storage treatments and were germinated in vitro after 1, 3, 7, 9, 12 and 18 months of treatment. Oospores of Chara muelleri and C. australis germinated after storage, Nitella cristata var. ambigua germinated only in the control treatment and Nitella subtilissima did not germinate at all. Highest germination of C. muelleri (76%) occurred after oospores were subject to fluctuations in light intensity and temperature, whereas highest germination of C. australis (41%) occurred after oospores were kept wet for 4 months. Small oospores (680 mu m) of C. muelleri germinated sooner than large (1000 mu m) oospores after 1 month of storage. Oospores of C. muelleri that were stored for a short period of time (1 month) germinated faster and more synchronously than did oospores that were stored for longer. Charophytes in these temporary wetlands reduce the risk that all offspring will die in one unfavourable season by contributing to a dormant oospore bank and by having a pattern of germination that increases the likelihood of survival. Oospore germination patterns can help explain the distribution of charophytes in space and time.