Nonstructural carbohydrate storage strategies in coexisting evergreen and deciduous conifers along an altitudinal gradient

In harsh high-altitude environments, trees tend to allocate more carbon to storage to ensure survival and growth under adverse conditions. However, the carbon allocation strategies of coexisting evergreen and deciduous conifers in high-altitude environments remain poorly understood. In this study, we investigated Larix principis-rupprechtii and Picea meyeri, two dominant treeline species naturally distributed on the Wutai Mountain, China. We measured the concentrations of soluble sugar, starch, and nonstructural carbohydrates (NSC) in one-year-old needles, one-year-old branches, and stems at different altitudes (approximately 1800–2750 m a.s.l.). Our results revealed that L. principis-rupprechtii showed higher NSC concentrations in both branches and stems compared with P. meyeri, whereas the NSC concentrations in the needles were similar between the two species. The concentrations of NSC and their components in most organs of L. principis-rupprechtii and P. meyeri did not decrease with increasing altitude; instead, they often increased near the treeline. In addition, compared with P. meyeri, which maintained relatively stable NSC concentrations across altitudes, L. principis-rupprechtii showed marked fluctuations among organs along the altitudinal gradient, indicating greater sensitivity to environmental variation. These findings demonstrate that L. principis-rupprechtii maintains higher NSC concentrations than P. meyeri and actively accumulates NSC under harsh environmental conditions, which may represent a physiological strategy enabling L. principis-rupprechtii to survive and persist at higher altitudes.