Effect of temperature and moist conditions on seed dormancy cycling of two sympatric limestone species,Begonia guishanensisandParaisometrum mileense,in southern China

Information about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, includingBegonia guishanensisandParaisometrum mileense, two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15 degrees C as well as moist chilling (MC) at 15/5 degrees C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40-65% ofB. guishanensisand 5% ofP. mileenseseeds were dormant at maturity. DAR at 25/15 and 15/5 degrees C as well as MC and WD cycles at 15/5 degrees C alleviated dormancy forB. guishanensisbut notP. mileense, and WD cycles at 25/15 degrees C induced a deeper conditional dormancy for both species. Seeds ofB. guishanensisexhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO(3)mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures forB. guishanensis.The field experiment indicated that seeds ofB. guishanensismay be able to form a persistent soil seed bank, while almost all seeds ofP. mileensegerminate at the beginning of the wet season in the field.