Abstract:

Objective: Non-structural carbohydrates (NSC) reserves support tree metabolism and growth when current photosynthates are insufficient, offering resilience in times of stress. Thus, investigation of seasonal dynamic patterns of NSC and the components and the allocation relationship among different organs of trees will help us to better understand the mechanism of carbon allocation in the process of tree growth. Method: In this study, the contents of NSC and its components in coarse roots and stems of the dominant species, Quercus variabilis, in the eastern part of Qinling Mountains, China in growing season and non-growing season were determined. The experiment was conducted from May 2016 to June 2017.We collected samples at semimonthly/monthly intervals during the leaf unfolding period from March to May, atmonthly/bimonthly during the leaf full growing season from June to November, and by one time during non-growing season in February. A total of approximately 130 samples were used to determine their NSC concentrations by Anthrone-sulfuric acid method and the correlations between coarse roots and stems in NSC concentrations were analyzed. Concurrently, the leaf phenology was monitored by direct observation. Result: 1) The contents of NSC and its components in coarse roots and stems of Q. variabilis were significantly different with time(P < 0.05), and the mean content of NSC in coarse roots(13.96%)was much higher than that in stems(6.24%), which was mainly related to the functional differences between the two organs. 2)There were positive correlations in NSC, soluble sugar contents and the ratio of soluble sugar to starch between coarse roots and stems(P < 0.05), but no significant correlation in starch concentration between them. 3)The peak value of NSC concentration in stems occurred in March, whereas that in coarse roots did in February, lagging behind about half a month. This difference between two organs could be explained by the carbon coordination between coarse roots and stems.The increase of stem NSC was synchronized with the decrease of thick root NSC, which followed by carbon demand for annual stem growth initiation. As a ring-porous tree, Q. variabilis leaf bud burst generally occurs after stem growth. Thus, before leaf unfolding, coarse roots provide NSC for the stem growth. Conclusion: The NSC concentrations in the coarse roots and stems of Q. variabilis has an obvious seasonal dynamic change. The species shows coordinated response of carbon storage and growth between coarse roots and stems.

Key words: non-structural carbohydrates, Quercus variabilis, seasonal dynamics, coarse root, stem, coordination