Seed dormancy increases population persistence in an annual plant in an environment-dependent manner

BACKGROUND AND AIMS: Seed dormancy can delay germination timing to more favorable growth conditions, either within years (seasonal dormancy) or across years (between-year dormancy), not only increasing seedling survival, but potentially increasing lifetime fitness. As such, seed dormancy can be a form of seasonal environmental tracking. In addition, seed dormancy can act as a bet-hedging strategy by spreading the germination risk across time, within or between years. Through both environmental tracking and bet-hedging, seed dormancy is hypothesized to stabilize population demography, potentially enhancing long-term population persistence. METHODS: To test whether populations that express high seed dormancy are more likely to persist than populations with low seed dormancy, we established genetically variable, experimental field populations of Arabidopsis thaliana that differ in their level of seed dormancy. Four environmental treatments were imposed to test for demographic differences in different environments and to test whether dormancy mitigates the effects of environmental variation. KEY RESULTS: Seasonal seed dormancy influenced demography and population persistence primarily via early seedling or rosette mortality. High Dormancy populations had larger seedling populations and higher population persistence over the three years in the most permissive environmental treatments. However, stressful environments-namely those which were consistently unfavorable for early life stages-diminished the demographic effects of dormancy. These dynamics, in turn, resulted in High Dormancy populations unexpectedly exhibiting more variation across environmental treatments than Low Dormancy populations. Therefore, dormancy's enhancement of demographic performance may be limited to environments that have at least some seasons or years that are favorable for early life stages. CONCLUSIONS: Seasonal seed dormancy may help populations persist over time, but not under all environmental conditions. In more permissive environments, dormancy can reduce population bottlenecks and maintain larger populations. Some conditions, however, may be too adverse for seed dormancy to overcome.