[Estimating nonstructural carbon content of tree crown considering its spatial variability: A case study on Juglans mandshurica and Ulmus japonica].

Using Juglans mandshurica and Ulmus japonica as test materials, we examined the variability in nonstructural carbohydrates (NSC) concentrations in the branches with different basal diameters with a branch analysis method and explored potential errors in estimating the crown-scale NSC content introduced from various sampling protocols. The results showed that organs significantly influenced the crown NSC concentrations for both species. The mean concentrations of the sum of soluble sugars and starch (TNC) of the leaves, new twigs, old branches, and dead branches were 17.6%, 12.6%, 5.7% and 2.9%, respectively. Most of the NSC concentrations in leaves and new twigs varied insignificantly with basal diameter, age, length and height of the branch. However, the NSC concentration in old branches increased significantly with decreasing the basal diameter, age and length of the branch, and with increasing the relative height of the branch. Among the branch traits, basal diameter was the best predictor for the NSC concentration of the old branch (the R2 between 0.87 and 0.95). The mean TNC contents of leaves, new branches, and old branches for the two species accounted for 28%, 2% and 70% of the crown TNC content, respectively. Considering the effect of the spatial variability in the estimation of NSC content, we recommend the sampling protocol that applies the NSC concentration of new twigs and old branches with a diameter of 3 cm to up-scale the crown NSC content as a simple and practical method.

[Spatial variation of non-structural carbohydrates in Betula platyphylla and Tilia amurensis stems].

Taking the two diffuse-porous tree species Betula platyphylla and Tilia amurensis in a temperate forest in Northeast China as test objects, this paper studied the spatial variation of the non-structural carbohydrates (NSC) concentrations in the stem xylem after leaf-fall. For the two tree species, the concentrations of total non-structural carbohydrate (TNC, soluble sugars plus starch) and soluble sugars in the stem xylem decreased gradually with the increasing depth from cambium to pith, whereas the starch concentration showed little radial variation. There was still a substantial amount of NSC in the inner wood close to pith. The concentrations of the NSC in the two species stems decreased gradually from the stump to the breast height, and then increased vertically. The maximum concentrations of the TNC, soluble sugars, and starch occurred at different heights, depending on the species and the TNC components. The ratio of sugar to starch showed a contrasting vertical trend for the two species, i. e., increasing from the stump to the top for B. platyphylla, but decreasing for T. amurensis. The estimation error of the stem NSC storage was mainly from the axial variation, and then, from the radial variation of NSC concentration. The TNC concentration (1.0% dry mass) in the stem of shade-intolerant species B. platyphylla was significantly lower than that (4.3% dry mass) of shade-tolerant species T. amurensis, which could be related to their different life-history strategies. Applying the sampling protocols considering the axial and radial variations of NSC could effectively reduce the potential uncertainty in estimating the NSC storage at tree or stand level.