DOI: 10.5061/dryad.2z34tmpqq
title: Global variation in nonstructural carbohydrate stores in response to climate

description: 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 NSCs that 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 reservoirs 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.
description: The data used for our analysis were initially collected in a
 database of NSC measurements, published in 2016 (Martínez-Vilalta et al.,
 2016), then updated by us to include articles through April 2020. To
 begin, we conducted a search on Web of Science (accessed April 6, 2020)
 for the following word combinations in any field of the articles “(NSC OR
 TNC OR starch OR carbohydrate*) AND (plant* OR shrub* OR tree* OR seedling
 * OR sapling*) AND (seasonal* OR temporal*). Our search yielded 1,040
 articles, of which we reviewed the abstracts to further only include
 measurements taken on wild species (none under cultivation) under natural,
 field conditions. Where a paper reported the results of a natural or
 under-field conditions experiment, we only included the control samples in
 our analysis. We further only examined papers that took at least (1) three
 measurements over time of the same individuals or populations and (2) ran
 for at least four months or more. Finally, due to a lack of data in some
 categories and to keep comparisons consistent, we further limited studies
 to only those done on (3) woody land plants and (4) mature trees (as
 defined by the authors of each study), (5) where the tissue sampled was
 not bark, phloem, or cortex, and (6) the organ sampled was the branch,
 coarse root, or stem. The age of the tissue itself can also affect the
 amount of NSC stores (Carbone et al., 2013; Furze et al., 2019); in our
 database, all stem results included are the sapwood, typically the outer
 2cm of the core, and only two studies that eventually made it to our final
 cut specified whether branches were current or previous years. Given these
 branch NSC concentration values of current versus older branches were all
 within 2–3 mg/g of each other, we averaged them together.
 All data were taken from the text, tables, supplementary data
 repositories, or the figures. For figure data extraction, we employed the
 software WebPlotDigitizer (Rohatgi, 2021). NSC data were converted to
 standard units of milligrams NSC per gram dry weight (mg
 g<sup>-1</sup>) and reported as soluble sugars and starch. The
 composition of soluble sugars may vary depending on method (Landhausser et
 al., 2018; Quentin et al., 2015), but they are largely composed of
 glucose, fructose, and sucrose (G. Hoch et al., 2003). Soluble sugars and
 starches were added to estimate total NSC (referred to throughout as NSC).
 For our following climate analyses, we examined NSC (SS + starch), SS, and
 % SS (SS / NSC).