Abstract: Understanding the carbohydrate reserves in root is necessary for the accurate estimation of carbon allocation between aboveground and belowground organs. Here, we investigated the seasonal variations of non-structural carbohydrates (NSC) and its components (soluble sugar and starch) in coarse roots of Chinese cork oak (Quercus variabilisBlume) at two altitudes (650 and 970 m) in eastern Qinling Mountain. Root samples were collected for 14 times at a biweekly/monthly interval from May 2016 to June 2017. The results showed that the concentrations of NSC and its components in Q. variabilis coarse roots had a significant seasonal variation at both altitudes (P<0.05), except for the starch at high altitude. The maximum concentrations of NSC in coarse roots appeared at the non-growing season (February), and declined at the beginning of the growing season (March). Starch was the major contributor to total NSC in oak coarse roots, accounting for 61% and 71% of the total NSC at high and low altitudes, respectively. As the reservoirs for future use, higher content of starch in coarse roots would support carbon resource and guarantee tree growth in the next year. There was a significant difference in the NSC concentrations of Q. variabilis coarse roots between high and low altitudes (March, P<0.05). Overall, the NSC concentration of Q. variabilis was lower at high altitude (10.26%) than that of the low altitude (13.96%). Seasonal fluctuations of NSC in coarse roots of Q. variabilis were consistent with the tree’s phenological rhythms. The storage of NSC in coarse roots at the end of the growing season and the non-growing season is important for the onset of tree growth in the following year. Our results help understand the mechanism of carbon supply from underground organs to tree growth.

Key words: Quercus variabilis, soluble sugar, starch, soluble sugar to starch ratio, intra-annual dynamic change.