Abstract:

【Objective】Non-structural carbohydrates (NSC) are important carbon reserves in trees, which are good indicators of tree carbon surplus or shortage stored. Research into the allocation of NSC contents among tree tissues will help to understand the mechanisms of carbon allocation within trees. This provides a scientific basis for further evaluation of the carbon sequestration potential of forest communities. 【Method】We conducted a field observational study by monitoring the NSC concentrations in the leaves and branches of Chinese cork oak (Quercus variabilis), and by synchronously observing the leaf phenology of those trees in some uneven-aged secondary oak forests growing in the east Qinling Mountain Range. By measuring the leaf length and fitting the leaf growth curve with the Gompertz function, the specific dates of the main phenological stages of leaves can be obtained. Sampling intervals were set semi-monthly/monthly during the leaf unfolding period from March to May, and monthly or bimonthly during the trees’ full growing season from June to November. The time series of observations and sampling spanned from May 2016 to June 2017. The content of NSC and its components in the leaves and branches of Q. variabilis was determined by the anthranone-sulfuric acid method. 【Result】① The dynamics of the content of NSC and its components in leaves and branches of Q. variabilis varied significantly with seasonal rhythms (P < 0.05). The average NSC content (mass fraction) in the leaves (8.94%) was higher than that in the branches (7.90%). ② The composition of NSC in leaves and branches of Q. variabilis was mainly soluble sugar, and comprised 62.5% and 63.5%, respectively. This physiological feature might be a life strategy for Q. variabilis, a deciduous tree species growing typically in the warm temperate zone, to survive in the local environment. ③ Significant differences in the NSC contents and their components between leaves and branches were observed mainly in the early (April-June) and late (October) growing seasons. Before entering the growing season, the NSC content of branches dropped rapidly to supply energy to bud-break and leaf development. In contrast, the leaves began to accumulate NSC by photosynthesis. In the late growing season, branches were inclined to store carbon to reconstruct the canopy for the next year. While, photosynthesis of leaves was reduced. ④ The Pearson correlation coefficients of the NSC content and their components between leaves and branches were not significant except for the ratio of soluble sugar to starch. The variation trend of NSC contents in leaves and branches was highly positive (R=0.986, P < 0.001) in the early growing season (March-June), but there was a time lag of 15-20 days.【Conclusion】It could be inferred that the distribution relationship of NSC contents between leaves and branches of Q. variabilis is not linear, but most likely non-linear. Therefore, when estimating the carbon sequestration potential of Q. variabilis, the nonlinear relationship of carbon distribution among different tissues should be comprehensively considered.

Key words: Quercus variabilis, non-structural carbohydrates (NSC), soluble sugar, starch, leaf, branch, carbon distribution