Comparing the intra-annual radial growth of three temperate species as related to leaf phenology

The complex interplay between primary and secondary growth processes in trees holds paramount significance in unraveling the physiological connections within distinct tree tissues. In this study, we continuously monitored the intra-annual radial growth of Pinus koraiensis , Quercus mongolica , and Betula platyphylla in Changbai Mountain of northeast China using microcore techniques from April to September 2021. Additionally, we used existing leaf phenology models to simulate the seasonal variations of leaf area of three species. Our results revealed substantial difference in radial growth dynamics and leaf expansion patterns among the different wood species. Notably, a synchronization between leaf expansion and radial growth was observed in certain phases for pine and birch, with a significant positive correlation between the rates of leaf expansion and radial growth. Conversely, oak exhibited no synchrony between leaf development and radial growth. Temporal disparities between cambial phenology and leaf phenology were observed. Specifically, for pine, leaf unfolding occurred prior to the onset of wall-thickening, while leaf shedding took place after the cessation of lignification. Oak exhibited a delayed leaf unfolding compared to the initiation of secondary wall formation, and leaf shedding notably occurred later than the cessation of radial growth. In contrast, birch displayed an earlier leaf unfolding in comparison to the onset of radial growth, and the cessation of lignification was later than leaf shedding. These findings indicate the diversity in physiological mechanisms and survival strategies among different wood species. Our results suggest that radial growth in pine and birch appears to be heavily reliant on photosynthetic activity of leaves, while oak places greater emphasis on carbon storage, particularly during early growing season. The findings provide new insights into the complex mechanisms of tree growth and are critical for predicting future species suitability in temperate forests.