A simulation model for seasonal changes in dormancy and germination of weed seeds

A model has been developed to simulate the annual dormancy cycle of seeds o f light-requiring species in the seed bank and the germination of exhumed s eeds after irradiation. Simulation of dormancy and germination is based on a physiological model concerning the action of phytochrome in the seed. Dor mancy is related to the amount of a hypothetical phytochrome receptor, whic h fluctuates in an annual pattern. Relief of dormancy is equivalent to an i ncrease in the amount of receptor, and induction of dormancy is equivalent to a decrease in the amount of receptor. Annual changes in temperature are the driving force for annual changes in the amount of phytochrome receptor in seeds that are buried in the seed bank. From the average amount of phyto chrome receptor in the seeds of a population, the model calculates the germ ination percentage that is reached when a seed sample from the population i s exhumed, irradiated and incubated at a given temperature in darkness. In the model, relief of dormancy results in a widening of the range of tempera tures over which germination can occur, and induction of dormancy results i n a narrowing of this range. Model parameters were estimated by fitting the model to data from a burial experiment with seeds of Polygonum persicaria L., Chenopodium album L. and Spergula arvensis L. At regular time intervals during 3 years, subsamples of these seeds were exhumed and tested for germ ination in the laboratory. The simulation model gave a good description of the observed cyclic changes in germinability of exhumed seeds.