A quantitative analysis of seed responses to cycle-doses of fluctuating temperatures in relation to dormancy:: Development of a thermal time model for Polygonum aviculare L. seeds

The sensitivity of Polygonum aviculare L. seeds to the dormancy-breaking effect of cycle-doses of fluctuating temperature changes as seeds lose dormancy due to storage under stratification temperatures. Sensitivity changes during seed stratification were characterized by a decrease in the number of cycles required to saturate the germination response, and by a progressive loss of the requirement for temperature fluctuations for dormancy breakage in increasing fractions of the seed population. The rate of these changes was dependent on the temperature at which seeds were stored for stratification; lower storage temperatures produced higher rates of change than higher storage temperatures. Germination curves, obtained in response to the effect of fluctuating temperature cycle-doses for seeds stratified at variable temperatures and times of storage, were brought to a common stratification thermal time (S-tt) scale by accumulating thermal time units under a threshold temperature for dormancy loss to occur. Results showed that those seeds that had accumulated similar S-tt units during stratification under different storage temperatures presented a similar germination response. Therefore, response-curve functions were adjusted to germination data of exhumed seeds that had accumulated similar S-tt, obtaining a family of germination response curves in relation to S-tt accumulation during storage. Based on these results, a simulation model was constructed relating dynamic changes in the parameters that determine germination response curves in relation to S-tt accumulation. The model was tested against independent data, showing a good description of the dynamics of changes in the fraction of the seed population requiring temperature fluctuation for dormancy breakage as dormancy release progressed.