Multi-Dimensional Patterns of Variation in First-Order Shoot Traits of Larix principis-rupprechtii in Northern China

As the most active fundamental unit in the aboveground branching system of woody plants, it remains unclear the relative importance of acclimation at the level of allocation and morphology in shoots. Additionally, the main dimensions of trait variation in shoots and whether their trait relationships conform to the common assumptions of the root economics spectrum (RES) have not yet been established. By collecting 1551 larch shoots, we measured and estimated five functional traits, including shoot diameter (SD), length (SL), dry matter content (SDM), specific stem length (SSL), and stem tissue density (STD). Furthermore, we assessed the relationships between bivariate and multivariate traits through a Pearson correlation analysis and principal component analysis (PCA), including standardized major axis (SMA) regression analysis. We found that SDM exhibited the greatest degree of variation. Meanwhile, SL and SDM were significantly and strongly positively correlated with SD. In contrast, SSL and STD were significantly negatively correlated with SD, and SSL and STD showed a weak positive correlation. In addition, these five functional traits were distributed across two nearly orthogonal (independent) principal component analysis (PCA) axes. These results revealed that shoots generally exhibit greater flexibility in altering their biomass allocation compared to their morphology. Meanwhile, the variation in shoot traits is associated with two main dimensions: a diameter-related dimension potentially integrating shoot construction, maintenance, and persistence, and the other dimension consisting of SSL and STD traits representing shoot plastic responses to the environment. And the relationship between SD and STD does not support the predictions of the root economics spectrum (RES). Our study may offer a promising pathway for better understanding the functions and ecological strategies of shoots.