How do montane plants manage to survive? Inferring from non-structural carbohydrates

Key message

Non-structural carbohydrates are distributed and stored in various organs, enabling plants to make a trade-off between “growth” and “resistance”, with temperature variation as the main driver.

Abstract

Non-structural carbohydrates (NSC) are important physiological indicators of carbon balance in plants and play a crucial ecological function in determining how plants respond to environmental changes. However, less is known about the mechanisms by which NSC change along the montane vertical climate belt gradient. In order to address this question, we investigated changes in NSC of 12 major tree species along the elevational gradients in the Sygera Mountains, southern Qinghai–Tibet Plateau. During the growing period (July–August) and dormant period (November–December) of the same phenological period, 64 woody plants were sampled for leaves, branches, trunks, and root organs. The contents of NSC, C, N, P, and K, and the main climatic factors were measured to detect the spatial and temporal characteristics of NSC content in woody plants in different elevations as well as their linkages. The results were as follows. (1) Plants seasonally allocate soluble sugars and starch. During the growing period, plants tend to store fewer non-structural carbohydrates to meet other carbon-demanding processes, such as growth or fruiting. During the dormant period, plants are committed to resisting stress and surviving winter through cooperative relationships (conversion of starch to soluble sugars). The physiological process of starch conversion to sugar may depend on whether starch concentration exceeds 5%. (2) The increasing NSC content of numerous tree species from the montane warm temperate belt to the alpine belt supports the “growth limitation” hypothesis, while the roots and leaf organs of woody plants have the most abundant carbon storage. (3) Plant nutrients (N, P, and K) promote the synthesis of NSC and regulate the quantity of soluble sugars and starch to establish a dynamic carbon balance in plants. (4) Plants accumulate NSC carbon pools in response to environmental stress (drought or low temperatures). “Low-temperature” stress is the primary factor limiting the growth of woody plants. Thus, temperature drives changes of NSC in woody plants across different elevations, while the physiological process of converting starch into soluble sugars (when starch content exceeds 5%, starch can be converted into soluble sugars) is an important mechanism that increases the tolerance of plants to abiotic stress.