Non-structural carbohydrates (NSC), such as soluble sugars and starch, are important for driving physiological function and survival in woody plants. The soluble sugar and starch in fine roots (< 2mm) might affect their resource acquisition, but little is known about their direct association with the fine root physiological function. Here, we were to explain the relationship of each NSC with fine root respiration and morphological traits of Abies mariesii and Betula ermanii under the alpine treeline. We measured the concentration of soluble sugar and starch, root respiration rate, and specific root length (SRL) in three root diameter classes: < 0.5, 0.5-1.0, 1.0-2.0mm. In both species, the sugar concentration of < 0.5 mm class of roots was lower than that in 0.5–2.0mm roots, while there were no significant differences in starch concentration among them. Additionally, our results show that the sugar concentration was negatively correlated with the root respiration rate and SRL, but not the starch. Altogether, these findings suggest that the soluble sugar of fine roots can act as a direct source of energy for the roots to aid soil resource acquisition, whereas the starch can as serve as an indirect, longer-term storage reservoir.