Setaria faberi Seed HeteroblastyBlueprints Seedling Recruitment: III. Seedling Recruitment Behavior

Seedling recruitment of heterogeneous Setaria faberi seed entering the soil post-abscission is elucidated herein. This is the third in a series of three articles providing evidence that weedy Setaria seedling recruitment behavior is predicated on dormancy state heterogeneity at abscission (seed heteroblasty), as modulated by environmental signals. Complex oscillating patterns of seedling emergence were observed during the first half of the growing season in all 503 soil burial cores of the 39 populations studied. These patterns were attributed to six distinct dormancy phenotype cohorts arising from inherent somatic polymorphism in seed dormancy states (canalized phenotypes). Early season cohorts were formalized using a mixture model consisting of four normal distributions. Two, numerically low, late season cohorts were also observed. Variation in emergence patterns among Setaria populations revealed a fine scale adaptation to local conditions. Seedling recruitment patterns were influenced by both parental-genotypic (time of embryogenesis) and environmental (year, common nursery location, seed age in the soil) parameters. The influence of seed heteroblasty on recruitment behavior was apparent in that S. faberi populations with higher dormancy at the time of dispersal had lower emergence numbers the following spring, and in many instances occurred later, compared to those less dormant. Heteroblasty was thus the first determinant of behavior, most apparent in recruitment number, less so in pattern. Environment modulated seedling numbers, but more strongly influenced pattern. The resulting pattern of emergence revealed the actual “hedge-bet” structure for Setaria seedling recruitment investment, its realized niche, an adaptation to the predictable mortality risks caused by agricultural production and interactions with neighbors. These complex patterns in seedling recruitment behavior support the conjecture that the inherent dormancy capacities of S. faberi seeds provides a germinability ‘memory’ of successful historical exploitation of local opportunity, the inherent starting condition that interacts in both a deterministic and plastic manner with environmental signals to define the consequential heterogeneous life history trajectories.