Coordinating flowering and germination across seasonal environments: linked process-based models predict genotype and environment specific life history expression

Background/Question/Methods

Plants in seasonal environments must be able to time developmental transitions to avoid mortality risk and maximize fecundity. Accordingly, plants are very responsive to seasonal environmental variables such as temperature, moisture, and photoperiod that are predictive of future conditions. In the model plant A. thaliana, environmental variables combine to shape timing of flowering in a way that is well understood and highlights the importance of germination timing in determining flowering time. However, we know almost nothing about how these two timing mechanisms systematically interact in an environmental context to determine plant life-history expression and population dynamics. Germination timing has been successfully modeled by agronomists via an environment-driven framework similar to the photo-thermal model used to predict A. thaliana flowering behavior. Each of these frameworks can accommodate genotypic differences in response, but existing germination models explicitly incorporate variation in dormancy level within cohorts of genetically identical seeds allowing variation in germination timing within a seed cohort (widely observed empirically). Here we integrate these models to explore coordination of flowering timing and germination timing in four locations across the A. thaliana European range.

Results/Conclusions

In this coordinated life cycle model, local environmental conditions shape clear seasonal patterns of germination/flowering/seed dispersal timing. Environments at the southern and northern edge of the species range allow for fewer generations in a year but for disparate reasons e.g. poor conditions for germination vs. longer vegetative life cycle and less time for dormancy loss. We demonstrate that even small variation in dormancy level within a seed set can create wide variation in life-cycle expression and that changes in dormancy level have much larger effects on average life cycle length than changes in initial floral repression. Further with our simple environmentally driven equations we can recreate three empirically observed life history patterns in A. thaliana 1. a southern to northern cline in dormancy level, 2. a switch to perenniality via seed banking in northern populations, and 3. the possibility of a "rapid cycling" life history in the central portion of A. thaliana's native range but not at the edges. We also generate novel hypotheses for how changes in dormancy and flowering behavior will interact to define life-cycle in highly divergent environmental conditions. Lastly we emphasize that while we are using a widely studied plant for our analysis, the linking of mechanistic, environmentally driven phenology models should be generally useful across a diversity of species for many applications.