Postdoctoral Scholar Donald Danforth Plant Science Center SAINT LOUIS, Missouri
Body of Abstract: Resource allocation drives the above-ground distribution of mass in grass plants across discrete developmental units called phytomers. Although the number of phytomers varies in genetically-identical grasses, plants with relatively more phytomers may not exhibit an increase in total biomass or height. To understand what may be driving this, we tracked the growth of 30 S. italica plants from genotypes B100 and A10.1. We experimentally observed that plants from the genotype B100 had between 20 and 22 phytomers, while plants from the genotype A10.1 had between 7 and 9 phytomers. B100 plants with more phytomers (e.g., 22) did not grow taller or have more total leaf length, despite having more leaves than plants with fewer phytomers (e.g., 20). A10.1 plants with more phytomers (e.g., 9) did grow taller and had more total leaf length than those with fewer phytomers (e.g., 7). We developed a dynamical model to determine if these patterns are emergent from the underlying growth structure. The model is parameterized using the number of phytomers and related developmental time parameters: leaf emergence, stem and leaf elongation time, panicle emergence, and flowering time. The model uses the semi-sequential nature of phytomer growth as its structure. The model predicts that the number of phytomers, the length of time each phytomer grows, and the shift to reproductive growth determines the allometric patterns. Together, model and data suggest that allometric patterns are driven by competition for resources between phytomers and the shift to reproductive growth in Setaria. The implications are expanded upon by further application to a wider range of Setaria genotypes, and predicting developmental time parameters from biomass growth curves.