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 Setariapopulations 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. faberipopulations 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 forSetaria 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. 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 mple x 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 popu...
Studies were conducted to determine the relationship between weedy Setariafaberi seed dormancy and subsequent behaviors in the soil culminating in seedling recruitment.This is the first in a series of three articles demonstrating weedy Setaria seed dormancy capacity heterogeneity at abscission (seed heteroblasty) provides a "blueprint" for those subsequent behaviours.The objective for this present article was to provide a robust characterization of seed heteroblasty at the time of dispersal for 39 locally adapted S. faberi populations, as influenced by parental genotype (time of embryogenesis) and environment (year, location). The heteroblastic structure of each population was revealed by the germination response to increasing amounts of after-ripening (in "ideal" conditions). The majority of the populations were differentiated from each other; this variation indicated a fine scale adaptation to different local environments.Taken together, the 39 responses represented Setaria's "seed dormancy phenotype space" and revealed three different generalized dormancy patterns. The first pattern, low dormancy populations, had high initial germination in response to low doses of after-ripening. The second, high dormancy populations, had no or low initial germination with little additional response to increased after-ripening. Most populations had the third pattern, intermediate to the others, with low initial germination and increasing germination with increasing after-ripening dose. Germination responses were also used to rank populations based on their dormancy level to facilitate later comparisons with emergence behavior. Heteroblasty at abscission, elucidated herein, is hypothesized to influence subsequent seed fates in the soil, the focus of the next two articles in this series
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 dormancygerminability 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. AbstractThe 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 germinatio...
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