Abstract: Non-structural carbohydrates (NSCs) are critical for plant drought adaptation, but their environmental drivers under prolonged drought remains unclear. We investigated seasonal NSCs dynamics in the leaf, stem and root of Picea crassifolia (Qinghai spruce) during the growing seasons of 2021−2023 under intensifying drought at three altitudes in Qilian Mountains, Northwest China. Our results revealed synchronous seasonal patterns in soluble sugar, starch, and total non-structural carbohydrate within the same year, contrasting with marked altitudinal disparities. As drought progressed (from 2021 to 2023), soluble sugars initially increased (2022) then declined (2023), while starch showed consistent reduction (except leaves). Moreover, the altitude of peak NSCs concentrations shifted from 3200 m in 2021 to 2700 m in 2023. In particular, prolonged drought alters the environmental factors affecting NSCs. NSCs demonstrated significant positive correlations with soil temperature during humid 2021, then negatively with air temperature, vapor pressure deficit, and precipitation during 2022’s initial drought, whereas under 2023’s persistent drought conditions, soil temperature and water content emerged as dominant drivers. Concurrently, the ratio of soluble sugar to starch transitioned from air temperature and precipitation associations (2021−2022) to soil parameter dependence in 2023. These findings provide new insights into the seasonal carbon dynamics of Qinghai spruce and the environmental response mechanisms under increasing drought stress, contributing to a better understanding of tree physiological adaptations in drought stress.

Key words: Non-structural carbohydrates, Evergreen conifer, Environmental factors, Drought · Arid mountains