Abstract:

Aims The study focused on Pinus koraiensis and Quercus mongolica in the broadleaf Korean pine forest of Changbai Mountain, investigating the seasonal dynamics of radial growth in both species and their response to non-structural carbohydrates (NSC).

Methods Seasonal sampling was conducted during the growing season (April to October), measuring the concentrations of soluble sugar, starch, and NSC in five components: branch, leaf, root, xylem, and phloem. Additionally, the micro-core sampling method was used to monitor the intra-annual growth dynamics of the xylem and investigate the potential relationship between NSC concentrations and xylem cell growth.

Important findings The main results are as follows: 1) There were significant differences in NSC concentrations between species, with P. koraiensis having higher NSC concentrations than Q. mongolica, and the range of variation in NSC concentrations being greater in P. koraiensis than in Q. mongolica. NSC concentrations in P. koraiensis were higher from May to September compared to March and April, while in Q. mongolica, NSC concentrations were higher from June to September compared to March to May. There were also notable differences in NSC concentrations between components within each species, with the pattern being phloem > leaf > branch > root > xylem. NSC concentration changes were most pronounced during periods of significant growth rate changes in P. koraiensis (April to June) and Q. mongolica (April to July), and once growth rates stabilized, NSC concentrations also became stable. 2) The intra-annual xylem cell growth dynamics of both Q. mongolica and P. koraiensis follow an “S” shape, with growth rate curves exhibiting an inverted “bell” shape. The maximum growth rate of Q. mongolica is higher than that of P. koraiensis, and its radial growth begins earlier (Day of year (DOY) 112 ± 2 vs. DOY 120 ± 1), ends later (DOY 252 ± 1 vs. DOY 241 ± 7), and has a longer growth duration (140 d vs. 121 d). 3) The radial growth rate of xylem cells in P. koraiensis shows a positive correlation with the NSC concentration in its components, while in Q. mongolica, the correlation is negative. The dynamic changes in growth rate and organ NSC concentration during different growth periods are as follows: during the early growth period (April to May), the radial growth rate of both species increases as the NSC concentration decreases. During the peak growth period (June), the xylem growth rate of P. koraiensis increases along with the NSC concentration, while the xylem growth rate of Q. mongolica increases as the NSC concentration decreases. After the peak growth period (July to September), NSC concentrations begin to accumulate again in both species. In conclusion, this study explored the NSC concentrations in different components and the intra-annual xylem growth dynamics of two major tree species, P. koraiensis and Q. mongolica, in the Changbai Mountains region, and found that NSC plays a key role in regulating xylem growth. The research revealed the coordinated relationship between NSC concentrations and xylem growth in both species, particularly the different carbon allocation patterns during the peak growth period. These findings provide new insights into the growth and carbon allocation mechanisms of trees in this region and offer important references for predicting the response of tree growth and carbon dynamics to future climate change.

Key words: non-structural carbohydrate, microcoring, radial growth, broadleaf Korean pine forest, Changbai Mountains