Seasonal patterns of nonstructural carbohydrate storage and mobilization in two tree species with distinct life-history traits.

Nonstructural carbohydrates (NSC) are essential for tree growth and adaptation, yet our understanding of the seasonal storage and mobilization dynamics of whole-tree NSC is still limited, especially when tree functional types are involved. Here, Quercus acutissima Carruth. and Pinus massoniana Lamb, with distinct life-history traits (i.e. a deciduous broadleaf species vs an evergreen coniferous species), were studied to assess the size and seasonal fluctuations of organ and whole-tree NSC pools with a focus on comparing differences in carbon resource mobilization patterns between the two species. We sampled the organs (leaf, branch, stem and root) of the target trees repeatedly over four seasons of the year. Then, NSC concentrations in each organ were paired with biomass estimates from the allometric model to generate whole-tree NSC pools. The seasonal dynamics of the whole-tree NSC of Q. acutissima and P. massoniana reached the peak in autumn and summer, respectively. The starch pools of the two species were supplemented in the growing season while the soluble sugar pools were the largest in the dormant season. Seasonal dynamics of organ-level NSC concentrations and pools were affected by organ type and tree species, with above-ground organs generally increasing during the growing season and P. massoniana roots decreasing during the growing season. In addition, the whole-tree NSC pools of P. massoniana were larger but Q. acutissima showed larger seasonal fluctuations, indicating that larger storage was not associated with more pronounced seasonal fluctuations. We also found that the branch and root were the most dynamic organs of Q. acutissima and P. massoniana, respectively, and were the major suppliers of NSC to support tree growth activities. These results provide fundamental insights into the dynamics and mobilization patterns of NSC at the whole-tree level, and have important implications for investigating environmental adaptions of different tree functional types.

[Community characteristics and stability analysis of secondary deciduous broad-leaved forest in Mopan Mountains, Jilin Province, China.] / 吉林磨盘山次生落叶阔叶林群落特征和稳定性分析.

The secondary deciduous broad-leaved forests in northeastern China were generally regenerated from the disturbed broad-leaved Korean pine forests, which are widely distributed in Changbai Mountains area. To understand their composition, structure and stability, a 5.76 hm2(240 m × 240 m) forest plot was established in the Mopan Mountains, Jilin Province in 2005, following the standards of the Center for Tropical Forest Science (CTFS). In this study, we analyzed the species composition, size class structure, survival curves of the main tree species and community stability of all woody plants with DBH ≥1 cm. The results showed that a total of 13368 individuals with DBH ≥1 cm were found, belonging to 39 species, 31 genera and 19 families. There were 12 species with importance value ≥1. The species composition was complex, with obvious characteristics of mixed broad-leaved forest. The abundance varied significantly among different species. The rare species and occasional species accounted for 23.1% and 43.6% of the total number of the species, respectively. The size distribution of all individuals showed a reverse "J" shape, which indicated that the community was in a stable and normal growth status. Fraxinus rhynchophylla, Quercus mongolica, Acer mono, and Maackia amurensis out of the six major species fitted reverse "J" form, Juglans manshurica showed an approximately normal distribution, and Ulmus japonica showed a "L" shape distribution. The survival curves of the six major tree species showed that the populations of F. rhynchophylla, Q. mongolica, A. mono, and M. amurensis were stable, J. mandshurica was declining, and U. japonica was growing. Results from the stability analysis of M-Godron indicated that the community was relatively stable at present.