A quantitative analysis of dormancy loss dynamics inPolygonum aviculareL. seeds: Development of a thermal time model based on changes in seed population thermal parameters

A model for simulatingPolygonum aviculareL. seed dormancy loss in relation to stratification temperature was developed. The model employs the lower limit temperature for germination (Tl) as an index of seed population dormancy status. While population mean forTl(Tl(50)) andTldistribution within the population (σTl) are allowed to vary as seeds are released from dormancy, other thermal parameters characterizing the germination thermal responses (base, optimal and maximal temperatures, and thermal time required for germination) and the higher limit temperature for germination (Th) are held constant. In order to relate changes inTl(50)and σTlto variable time and temperature, a stratification thermal time index (Stt) was developed, which consists of the accumulation of thermal time units under a threshold temperature for dormancy loss to occur. Therefore,Tl(50)and σTlvaried in relation to the accumulation ofSttaccording to time and temperature. To derive model equations, changes in seed population thermal parameters were estimated for buried seeds stored at 1.6, 7 and 12°C for 110 d. Seeds were exhumed at regular intervals, and were incubated at 15°C and at a gradually increasing temperature regime in the range 6–25°C. The germination time-course curves obtained were reproduced using a mathematical model. Thermal parameters that best fit simulated and experimentally obtained germination time-course curves were determined. Model performance was evaluated against data of two unrelated experiments, showing acceptable prediction of timing and percentage of germination of seeds exhumed from field and controlled temperature conditions.