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.
Woody plant species store nonstructural carbohydrates (NSCs) for many functions. While known to buffer against fluctuations in photosynthetic supply, such as at night, NSC stores are also thought to buffer against environmental extremes, such as drought or freezing temperatures by serving as either back‐up energy reserves or osmolytes. However, a clear picture of how NSCs are shaped by climate is still lacking. Here, we update and leverage a unique global database of seasonal NSC storage measurements to examine whether maximum total NSC stores and the amount of soluble sugars are associated with clinal patterns in low temperatures or aridity, indicating they may confer a benefit under freezing or drought conditions. We examine patterns using the average climate at each study site and the unique climatic conditions at the time and place in which the sample was taken. Altogether, our results support the idea that NSC stores act as critical osmolytes. Soluble Sugars increase with both colder and drier conditions in aboveground tissues, indicating they can plastically increase a plants' tolerance of cold or arid conditions. However, maximum total NSCs increased, rather than decreased, with average site temperature and had no relationship to average site aridity. This result suggests that the total amount of NSC a plant stores may be more strongly determined by its capacity to assimilate carbon than by environmental stress. Thus, NSCs are unlikely to serve as reservoir of energy. This study is the most comprehensive synthesis to date of global NSC variation in relation to climate and supports the idea that NSC stores likely serve as buffers against environmental stress. By clarifying their role in cold and drought tolerance, we improve our ability to predict plant response to environment.
more » « less- Award ID(s):
- 2010781
- NSF-PAR ID:
- 10390537
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 29
- Issue:
- 7
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 1854-1869
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Under prolonged drought and reduced photosynthesis, plants consume stored nonstructural carbohydrates (NSCs). Stored NSC depletion may impair the regulation of plant water balance, but the underlying mechanisms are poorly understood, and whether such mechanisms are independent of plant water deficit is not known. If so, carbon costs of fungal symbionts could indirectly influence plant drought tolerance through stored NSC depletion.
We connected well‐watered
Pinus ponderosa seedling pairs via ectomycorrhizal (EM) networks where one seedling was shaded (D) and the other kept illuminated (LD) and compared responses to seedling pairs in full light (L). We measured plant NSCs, osmotic and water potential, and transfer of13CO2through EM to explore mechanisms linking stored NSCs to plant water balance regulation and identify potential tradeoffs between plant water retention and EM fungi under carbon‐limiting conditions.NSCs decreased from L to LD to D seedlings. Even without drought, NSC depletion impaired osmoregulation and turgor maintenance, both of which are critical for drought tolerance. Importantly, EM networks propagated NSC depletion and its negative effects on water retention from carbon stressed to nonstressed hosts.
We demonstrate that NSC storage depletion influences turgor maintenance independently of plant water deficit and reveal carbon allocation tradeoffs between supporting fungal symbionts and retaining water.
