Date of Award
Doctor of Philosophy
Ecology and Evolutionary Biology
The relationship between weedy Setaria seed dormancy and subsequent behaviors in the soil culminating in seedling recruitment is elucidated. Weedy Setaria seed dormancy capacity heterogeneity (heteroblasty) at the time of dispersal was characterized for 45 locally adapted Setaria populations, as influenced by parental genotype (species, time of embryogenesis) and environment (year, location). Taken together, the 45 responses represented Setaria's "seed dormancy phenotype space". The fate of heteroblastic seed entering the soil post-abscission was studied in four of the populations. When dispersed, heteroblastic Setaria seeds introduced into the soil form long-lived pools with varying cycles of dormancy, germination and death. The initially highly dormant seed after-ripens with time and becomes highly germinable, awaiting favorable temperature and moisture conditions: the heterogeneous germination candidate pool. As this pool is depleted in the spring and early summer by seedling emergence and death, dormancy is re-induced in the living seeds remaining in the soil. Seeds remain dormant throughout the summer, then resume after-ripening during late fall. This dormancy-germinability cycle exhibited complexity within and among the Setaria populations studied. Heteroblasty was retained within populations, and germinability responses to the yearly seasonal environment varied among populations. Seedling emergence behavior revealed the actual "hedge-bet" structure for Setaria seedling recruitment, its realized niche, an adaptation to the predictable mortality events caused by agricultural production practices. Complex oscillating patterns of seedling emergence were observed during the first half of the growing season in all 45 populations. These patterns were attributed to four distinct dormancy phenotype cohorts arising from inherent somatic polymorphism in seed dormancy states, and formalized using a mixture model consisting of four normal distributions. Variation in these patterns among Setaria populations revealed a fine scale adaptation to local conditions. The observed complexities in seedling recruitment behavior support the conjecture that the inherent dormancy capacity provides a 'germinability memory', the inherent starting condition that interacts in both a deterministic and plastic manner with environmental signals to define the resulting heterogeneous life history trajectories, an indication of learning and intelligent behavior.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Kari Ann Jovaag
Jovaag, Kari Ann, "Weedy Setaria species-group seed heteroblasty blueprints seedling recruitment " (2006). Retrospective Theses and Dissertations. 1528.