Juniperus virginiana sourced from colder climates maintain higher ratios of soluble sugars to starch during cold...

Nonstructural carbohydrates (NSCs) are carbon compounds that serve a large variety of purposes, which makes it hard to disentangle how their concentrations change in response to environmental stress. Soluble sugars can accumulate in plants as metabolic demand decreases, e.g., in response to drought or as seasonal temperatures decrease. Alternatively, actively allocating to NSCs could be beneficial in cold acclimation (CA) or in periods of increased aridity because soluble sugars serve non-metabolic functions as cryoprotectants and in osmoregulation. We used Juniperus virginiana L., a woody plant currently expanding its range, to investigate whether plants sourced from colder and more arid locations maintained higher concentrations of NSCs. We sourced three populations of J. virginiana from across an environmental gradient, and we compared these with the closely related Juniperus scopulorum Sarg. We grew the plants in a common garden in north-east OH, part of J. virginiana's historic range. We exposed the plants to a drought treatment during the summer and then measured the NSC concentrations and cold-hardiness as the plants acclimated to colder temperatures and shorter days. We found that individuals originating from the warmer, more southern range edge were initially not as cold-hardy as plants from the other source populations and that they only reached similar hardiness after prolonged low temperatures. We did not find an effect of drought on NSCs, although this may be due to other traits conferring a high level of drought tolerance in J. virginiana. Across all plants, the NSC concentration increased over the CA period, specifically as sugars. Although the highest concentrations of sugars were found in plants from southern populations, the plants from colder environments maintained higher sugar-to-starch ratios. These results highlight the importance of NSCs in CA and that plants sourced from different climates showed different physiological responses to shortening days and low temperatures.