Abstract: Aims Analyzing the effects of mycorrhizal type and growth stage on fine root traits in temperate broadleaf tree species, and exploring trait trade-off strategies between two mycorrhizal types across different growth stages. Methods Five arbuscular mycorrhizal (AM) and five ectomycorrhizal (EM) tree species in the broadleaved-Korean pine (Pinus koraiensis) forest of Liangshui National Nature Reserve in Heilongjiang Province were selected. Five saplings and five mature trees of each species were chosen based on their diameter at breast height. The morphological, chemical and anatomical characteristics of their absorptive roots and transport roots were measured. Important findings The results show that: (1) The specific root length (SRL) and cortex thickness (CT) of the absorptive roots in AM tree species were significantly higher than those in EM tree species, reflecting a nutrient acquisition strategy centered on the root system itself; in contrast, EM tree species exhibited lower SRL in absorptive roots, while the stele diameter (SD) and C:N ratio in transport roots were significantly higher than those in AM tree species. The enhanced transport structure adapts to the needs of mycorrhizal fungi for long-distance nutrient transport, reflecting an “outsourced” resource acquisition strategy. (2) The N content in the absorptive roots of young trees was significantly higher than that of mature trees, while the C:N ratio was significantly lower than that of mature trees; however, there were no significant changes in morphological and anatomical traits, indicating that the effects of growth stage on absorptive roots are primarily achieved through adjustments in chemical traits. Phosphorus (P) content in the transport roots of mature trees was significantly higher than that of young trees, and the proportion of the stele in transport roots (PRS) was significantly higher than that in absorptive roots in both growth stages, demonstrating that transport roots ensure long-distance nutrient transport through the allometric growth of anatomical traits and the accumulation of phosphorus. (3) The fine root trait space of AM tree species showed a two-dimensional pattern: PC1 reflects the functional differentiation between absorptive and transport roots, while root tissue density (RTD) and N content on PC2 constitute an independent conservation dimension. Furthermore, the trait dispersion of absorptive roots in young trees is significantly higher than that in mature trees, indicating that their resource acquisition strategies possess greater plasticity; EM tree species fine root traits are highly integrated along a single dimension, RTD does not constitute an independent conservation dimension, and there is no significant difference in dispersion between young and mature trees, indicating that their resource strategies are conservation-oriented and integrated, which is conducive to long-term nutrient maintenance. The research results provide a scientific basis for understanding the nutrient acquisition strategies and growth adaptation mechanisms of the primary broadleaf tree species companion species broad-leaved Pinus koraiensis forests.

Key words: fine root traits, root functional modules, mycorrhizal type, growth stage, root economics spectrum