PS 15-203 - Non-structural carbohydrate allocation during cold acclimation: Individuals of Juniperus virginiana from colder climates maintain higher ratios of soluble sugars to starch during cold acclimation

Abstract: Non-structural carbohydrates (NSC)s are labile carbon compounds used by plants for metabolic demands, but also function to protect plant tissue from environmental stressors such as freezing temperatures. The concentration and make up of NSCs can change in response to environmental conditions as plants allocate resources into stress protection (soluble sugars) or energy storage (starch). During cold acclimation, these changes in NSCs is due to the combination of the down regulation on plant growth and increased sugar content to aid in cryoprotection. The timing and strength of cold acclimation responses may vary in plants originating from locations with different climate conditions may show differences in the timing and strength of cold acclimation responses. To examine NSC dynamics during cold acclimation we studied the evergreen conifer, Juniperus virginiana. The historic range of J. virginiana features a range of minimum and maximum temperatures and yearly precipitation totals. Notably, the species has recently expanded west past the 100^th meridian marking a significant change in climate compared to its historic range, featuring lower minimum temperatures and lower precipitation totals. We performed a common garden experiment using individuals of Juniperus virginiana from warm and cold locations from the historic species range (Florida, New Jersey) and from a cold location at the edge of recent range expansion (South Dakota), and a closely related species, J. scopulorum, that co-occurs in regions where J. virginiana has recently expanded.

Plants from warmer environments were not as initially cold hardy, however became equally cold hardy as plants from colder environments after prolonged low temperature exposure. Across all plants, the concentration of NSCs increased over the cold acclimation period, primarily as soluble sugars, with the plants from warmer environments experiencing the greatest increase (774.9%). Individuals from colder environments had significantly higher ratios of sugar to starch than plants from warmer environments. While sugar increases may be due to carbohydrate mobilization to fuel growth, this study provides evidence for increases in sugar levels to serve as osmolytes. Additionally, this study highlights the different strategies in resource allocation for plants originating from different environments. These results highlight the role of NSC in cold acclimation, and differences in cold acclimation kinetics based on climates or origin. Given the differences in climates our individuals originated from, the NSC allocation during cold acclimation is not driven by passive accumulation.