<i>Setaria</i> <i>faberi</i> Seed HeteroblastyBlueprints Seedling Recruitment: III. Seedling Recruitment Behavior

Abstract

Seedling recruit ment 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 recruit ment behavior is predicated on dormancy state heterogeneity at abscission (seed heteroblasty), as modulated by environmental signals. Co mplex 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 fro m inherent somatic poly morphis m in seed dormancy states (canalized phenotypes). Early season cohorts were formalized using a mixtu re 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 recruit ment patterns were influenced by both parental-genotypic (time of embryogenesis) and environmental (year, co mmon 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 follo wing spring, and in many instances occurred later, co mpared to those less dormant. Heteroblasty was thus the first determinant of behavior, most apparent in recruit ment nu mber, less so in pattern. Environ ment modulated seedling numbers, but mo re strongly influenced pattern. The resulting pattern of emergence revealed the actual hedge-bet structure for Setaria seedling recruit ment investment, its realized niche, an adaptation to the predictable mortality risks caused by agricultural production and interactions with neighbors. These comp lex patterns in seedling recru it ment behavior support the conjecture that the inherent dormancy capacities of S. faberi seeds provides a germinability 'memory' of successful historical exp loitation of local opportunity, the inherent starting condition that interacts in both a determin istic and plastic manner with environ mental signals to define the consequential heterogeneous life history trajectories.