Aims The content and allocation of nonstructural carbohydrates (NSC) in trees reflect whole-tree carbon balance regimes, and are crucial to determine growth / survivorship trade-off of trees and model tree carbon balance between uptake and investments in structure or loss. Our objective was to examine the concentration and allocation patterns of NSC for three temperate tree species, i.e., Korean pine (Pinus koraiensis), Dahurian larch (Larix gmelinii) and Mongolian oak (Quercus mongolica).
Methods During the mid-growing season (July of 2010), all biomass tissues, including foliage, branch, stem and root, were randomly sampled from three dominant trees for each species. The stem samples were taken from mid-canopy and breast height, and divided into sapwood and heartwood, while the root samples were divided into fine (diameter < 2 mm), medium (2–5 mm) and coarse roots (>5 mm). All samples were dried, ground, and analyzed for NSC concentrations (including soluble sugar and starch) with a modified phenol-sulfuric acid method.
Important findings The concentrations of NSC and its component differed significantly among species and tissues. Concentration ranges were 0.65–8.45, 1.96–5.95 and 3.00–13.90 g·100 g–1 DM for soluble sugar, starch, and NSC, respectively. On average, the contents of NSC and its components followed the order of: larch > oak > pine. Concentrations in the foliage and roots were higher than those in other tissues. Within the stems, the longitudinal variations in the concentrations of NSC and its components were insignificant, whereas the differences between sapwood and heartwood varied with species and NSC components. There was no significant difference in soluble sugar concentration between sapwood and heartwood, but significant differences in starch and total NSC concentration. The concentrations of NSC and its components varied insignificantly with root diameters for larch and pine, but significantly for oak. Oak invested more soluble sugar to aboveground growth, whereas the two conifers did more to roots. Nevertheless, starch was mainly reserved in stems, and the intra-tree allocation pattern of starch exhibited an opposite trend to soluble sugar, leading the total NSC to be relatively balanced between roots and
branches. In the stems, heartwood was the major reserve of NSC and starch, while sapwood was the major reserve of soluble sugar for the two conifers. In the roots, coarse root was the dominant reserves of NSC and its components. We concluded that the inter- and intra-specific variations in the NSC and its components in this study reflect differences in growth strategies and within-tree carbon source / sink strength for the three temperate tree species.