The role of environmental stressors on reproduction, seed morphology, and germination: A case-study of Northern White Cedar, Thuja occidentalis L.

Changes in resource allocation from parent to offspring can have effects on the dispersal, recruitment, and survival of progeny, with impacts sometimes extending across generations. In plants, environmental stressors not only impact the growth of mature individuals but can also alter the provisioning of resources to developing seeds, further extending to embryo development and reproduction. In this study, we compare seed biomass, morphology, seed set, and germination among two natural populations and three additional seed sources of Thuja occidentalis L. (northern white cedar), a fen-dependent species in the Chicago, Illinois region. Chicago Junior School and Trout Park were once contiguous populations, now bisected by the I-90 toll road, and are heavily impacted by human disturbance and external pollutants. Variation was observed in seed morphology, cone biomass, and seed set among study sites with Trout Park trees producing fewer seeds and smaller cones than any other site in our study. Despite morphological differences, germination was low overall except for commercial seed. Differences among the two neighboring sites implicate that Trout Park is disproportionately affected by environmental factors (e.g., road salts and altered hydrology) compared to Chicago Junior School, potentially impacting the growth and recruitment of T. occidentalis in these urban populations.