Effects of phenological changes on non-structural carbohydrates in leaves of dominant species in the cold temperate forest.

To investigate the impacts of phenological changes in cold-temperate zones on the concentrations of non-structural carbohydrates (NSCs) and their components in leaves, we selected dominant tree species from different forest communities (<i>Larix gmelinii</i> forest, <i>Betula platyphylla</i> forest, and <i>Populus davidiana</i> forest). Leaf samples were collected based on phenological rhythms to explore the influence of phenological changes on leaf NSCs. The results showed that the contents of soluble sugar, starch, and NSC in the leaves of the three tree species exhibited significant phenological changes. Soluble sugar content was significantly higher than starch content, accounting for 73.7% to 96.3% of leaf NSCs. As phenological rhythms changed, foliar NSC and soluble sugar contents in the three tree species showed a unimodal pattern, while starch content fluctuated. Foliar NSC content of the three tree species was the lowest at the early stage of leaf expansion. The NSC content of <i>P. davidiana</i> was the lowest among the three tree species. From full leaf expansion to the leaf discoloration phase, the NSC content in the leaves of <i>B. platyphylla</i> and <i>P. davidiana</i> was higher than that of <i>L. gmelinii</i>. The peak NSC content occurred during the leaf discoloration phase, with <i>P. davidiana</i> (151.36 g·kg^-1) > <i>B. platyphylla</i> (146.64 g·kg^-1) > <i>L. gmelinii</i> (132.20 g·kg^-1). During the leaf-fall period, the NSC content in the leaves decreased, with <i>P. davidiana</i> showing the largest decrease at 61.8%. Redundancy analysis indicated that soil temperature and available nitrogen content had significant effects on the NSC and its components. There were certain time differences in the phenological periods of the dominant species in the cold-temperate forest. The impact of phenological changes on leaf NSC content showed similar trends among different species, with the effect being more pronounced in <i>B. platyphylla</i> and <i>P. davidiana</i> than in <i>L. gmelinii</i>. Such a result indicated that different tree species in cold-temperate zones respond differently to climate change.