Relative position of seeds driven the seedling growth are mediated by root–leaf traits

Abstract Variations in plant traits are indicative of plant adaptations to forest environments, and studying their relationships with tree growth provides valuable insights into forest regeneration. The spatial arrangement of plant seeds within the forest litter or soil critically influences the variations of root–leaf traits, thereby affecting the adaptive strategies of emerging seedlings. However, our current understanding of the impacts of individual root–leaf traits on seedling growth in different relative position, and whether these traits together affect growth, remains limited. This study focuses on the dominant tree species, Castanopsis kawakamii, within the Sanming C. kawakamii Nature Reserve of China. The present experiment aimed to examine the variations in root–leaf traits of seedling, focus on the relative positions of seeds within different layers: beneath or above the litter layer, or within the bare soil layer (without litter). Our findings provided evidence supporting a coordinated relationship between root and leaf traits, wherein leaf traits varied in conjunction with root traits in the relative positions of seeds. Specifically, we observed that seedlings exhibited higher values for specific leaf area and average root diameter, while displaying lower root tissue density. The mixed model explained 86.1% of the variation in root–leaf traits, surpassing the variation explained by the relative positions. Furthermore, soil nitrogen acted as a mediator, regulating the relationship between seedling growth and root–leaf traits, specifically leaf dry matter content and root tissue density. Therefore, future studies should consider artificially manipulating tree species diversity based on root–leaf traits characteristics to promote forest recovery.