Setaria Faberi Seed Heteroblasty Blueprints Seedling Recruitment: II. Seed Behavior in the Soil

The fate of heteroblastic Setaria faberi seed entering the soil post-abscission is elucidated. Introduction of four populations of S. faberi seeds with heterogeneous dormancy capacities into the soil of a no-till Glycine max field resulted in the formation of enduring pools with varying cycles of dormancy, after-ripening, germination, dormancy reinduction and death. The buried seed rain of these highly dormant seed after-ripened with time and became highly germinable, awaiting favourable temperature and moisture conditions: the heterogeneous germination candidate pool. As this pool was depleted in the spring and early summer by seedling emergence and death, dormancy was re-induced in the living seeds that remained in the soil. These seeds remained dormant throughout the summer, then resumed after-ripening during late autumn. This dormancy-germinability cycle exhibited complexity both within and among S. faberi populations. Seed heteroblasty within S. faberi populations was retained, and germinability responses to the yearly seasonal environment varied among S. faberi populations. Further, local adaptation was shown by the differential germinability responses among S. faberi populations in common location agricultural nurseries. Seed mortality patterns also exhibited complexity within and among populations. Within an individual S. faberi population, mortality patterns changed as seeds aged in the soil. Among S. faberi populations differential mortality responses were observed in response to yearly seasonal environments and common nurseries. Observations of both germinability cycling and mortality are consistent with the hypothesis that S. faberi seed behaviour in the soil is predicated on dormancy capacity heterogeneity at abscission and modulated by the seasonal environmental conditions experienced in the field. The observations of seed fates obtained from heteroblastic seeds of four S. faberi populations buried at two common nurseries utilized a “bare core” technique. Cores were extracted periodically to determine seed fates. Inevitably, the fates of a fraction of those seeds could not be determined and were thus classified as unknown. Despite the equivocal nature of the unknowns they provided evidence that unaccounted seed losses were most likely not due to migration out of the core area. The lack of migration and high seed recovery (approximately 88.5%) emphasized the utility of the bare core technique in comparison to enclosed seed-soil cores.