Absorptive roots are indispensable, functioning as the principal organs for plants to absorb vital nutrients and water. The functional traits of absorptive roots are critically important, reflecting the strategies employed in belowground resource acquisition. While thinning has received considerable attention for its role in forestry management and its capacity to enhance forest microenvironments, a significant gap in research exists concerning the impact of thinning on root functional traits. This dearth of research is exceedingly detrimental, hindering a thorough comprehension of plant underground resource acquisition strategies. To comprehensively explore the effect of thinning on root functional traits and belowground resource acquisition strategies, this study focused on Korean pine (Pinus koraiensis) in mixed plantation (mixed with Populus cathayana) under thinning and control treatments in the Changbai Mountain forest area of Jilin Province, China. Absorptive root anatomical, morphological, and chemical traits were meticulously measured and subjected to detailed analysis. The intricate relationship among these functional traits was explored using principal component analysis (PCA). The findings revealed that: (1) concerning absorptive root anatomical traits, thinning exerted a significant influence. Thinning significantly increased cortical thickness of first to third order roots by 68.1%, 30.5% and 241.1%, respectively. Thinning significantly increased cortical thickness to stele radius ratio of first to third order roots by 69.0%, 52.0% and 252.1%, respectively, and significantly decreased stele diameter of second and third order roots by 13.2%, 24.2%, respectively. (2) regarding absorptive root morphological traits, no significant effect of thinning was found in root diameter, specific root length, specific root area and tissue density of first to third order roots. (3) regarding absorptive root morphological traits, thinning significantly increased nitrogen concentration of first to third order roots by 24.4%, 28.3% and 29.6%, respectively, and significantly decreased carbon to nitrogen ratio of first to third order roots by 17.0%, 20.2% and 22.2%, but no significantly effect was found in carbon concentration. (4) PCA revealed a trade-off in absorptive root strategies ranging from an opportunistic to a conservative approach, with the opportunistic approach fostering a swift root response to variable resource availability and the conservative approach bolstering the root's competitive ability. Under thinning treatment, absorptive roots aligned with the opportunistic strategy, whereas under control treatment, they aligned with the conservative strategy. To encapsulate, these findings suggest that thinning markedly influences absorptive root anatomical and chemical traits, bolsters their nutrient acquisition capabilities, and shifts the belowground resource acquisition strategies from a conservative to an opportunistic approach. This shift may due to thinning improves forest microenvironment and soil quality, root increase nutrient acquisition ability to provide nutrient for rapid growth of Korean pine. These findings provide a scientific basis for the management of Korean pine broadleaf forests and offer theoretical support for further research on the response and adjustment mechanism of belowground resource acquisition strategies to external factors.