Abstract: One major impact of global change on plants is the forward-shift of life history events like germination. A change in the relative timing of germination between species could also alter size-mediated competitive dynamics via changes in “priority effects”. Further, species that do not track an earlier spring will emerge into a warmer abiotic environment, which could also affect competitive dynamics. To test this I manipulated relative and absolute germination timing using a C3 and C4 grass species abundant in the Piedmont region of North Carolina and assessed effects on plant growth. I predicted that later absolute germination would favor the C4, the poorer competitor in the greenhouse, and increase the importance of relative germination timing. I analyzed results using ANOVA and forward model selection with AIC.
In the greenhouse, the C3 far outperformed the C4. Both species exhibited priority effects, measured with biomass. There was no effect of chamber temperature as an analog for seasonal timing, suggesting that biotic context of germination shaped performance outcomes more than abiotic context for both species. Field results contradicted this; in the field, the C3 was sensitive to absolute germination timing alone. For the C4, second-arrivers in the late-season treatment underperformed relative to all groups. Ongoing work aims to disentangle the drivers of differences between greenhouse and field results.
