Non-structural carbohydrates in root and stem show contrasting relationships with tree growth and drought resilience in a semiarid forest

BACKGROUND: Non-structural carbohydrates (NSCs) are central to plant carbon metabolism, acting as critical buffers that regulate tree growth and survival under environmental stress. In semiarid regions, increasing hydroclimatic variability poses significant challenges to forest sustainability. However, whether different NSC components (soluble sugars vs. starch) across distinct organs (aboveground vs. belowground) exhibit consistent relationships with tree growth and post-drought resilience remains poorly understood. We quantified soluble sugar and starch concentrations in leaves, branches, stems, and roots of four coexisting tree species in the Saihanwula Nature Reserve during the growing season. Principal component analysis, hierarchical partitioning, and linear mixed-effects models were combined with tree-ring-derived growth and drought resilience indices to evaluate the relationships between organ-specific NSC composition, radial growth, and drought resilience. RESULTS: We observed clear interspecific differences in NSC composition and drought resilience traits among the four coexisting tree species. Organ-specific NSC composition was more strongly associated with radial growth than with drought resilience. Within these relationships, organ-specific NSCs were explained as distinct functional specialization. Fine-root starch associated positively with radial growth and growth stability. Conversely, starch accumulation in stems was negatively associated with structural growth, strongly corroborating a growth-storage trade-off. In particular, readily metabolizable branch soluble sugars positively associated with post-drought growth recovery and hydraulic repairment following extreme water deficit. CONCLUSIONS: Our results suggested that NSC composition differed substantially among organs and species in this semiarid forest ecosystem. Soluble sugars and starch exhibited contrasting relationships with tree growth and drought resilience across aboveground and belowground organs. These findings highlight the importance of considering organ-specific NSC components separately when evaluating tree growth responses and drought resilience under increasing climate variability.