Quantifying the oxygen sensitivity of seed germination using a population-based threshold model

Seeds vary widely in the sensitivity of germination to oxygen (O2) partial pressure, depending upon the species, temperature, dormancy state and physiological status of the seeds. Most analyses of the O2 sensitivity of germination have focused on final germination percentages and estimated the O2 percentage in air that is required to reduce germination to a given percentage (usually 50%). In contrast, we have applied a populationbased threshold model utilizing time courses of germination to quantify three parameters related to seedgermination sensitivity toO2 availability: themedian base (or threshold) O2 percentage, the standard deviation of O2 thresholds among seeds in the population, and an oxygen–time constant that relates O2 percentage to germination timing. The model fits germination responses accurately across a wide range ofO2concentrations. The response toO2was logarithmic in all cases, with the O2 percentage required for 50% germination ranging from 21% to as low as 0.005%, depending upon the species, the temperature and the seed dormancy level. Modelling indicated that some seeds can adapt to low O2 percentages and shift their thresholds to lower valuesover time. Lower temperatures decreased the minimum O2 threshold, as did afterripening. Seed priming generally reduced the oxygen– time constant and increased the standard deviation of germination responses, but had relatively little effect on theO2 sensitivityper se. The population-based threshold model can be used to quantify the O2 sensitivity of seed germination and to predict germination rates and percentages when O2 availability is limiting.