Objective  Exploring the relationship between biodiversity and ecosystem functions (BEF) was proposed to be a central issue in ecology and a key prerequisite for multi-functional forest management. However, the specific mechanisms regulating biodiversity and forest carbon sink function relationship in broadleaved Korean pine forests were still not understood very well. Based on the observations from a 30 ha broadleaved Korean pine forest sample plot in Jiaohe, northeastern China, this study aimed to clarify how different facets of biodiversity (i.e., functional diversity and composition) influence forest carbon sink functions.

  Method  Functional diversity and composition were obtained from seven plant functional traits. A structural equation modeling (SEM) was performed to test three alternative hypothesized mechanisms, including niche complementary effect, biomass ratio effect and vegetation quantity effect, which had the potential to regulate the biodiversity and carbon sink relationship.

  Result  (1) Biodiversity is an important influencing factor of forest carbon sink function. Improving functional diversity will help to increase forest carbon increment, and increasing the proportion of slow growth conservative traits will help to increase forest carbon storage. Maintaining a certain stand density will also help to fully utilize resources and improve forest carbon fixation capacity. (2) The results also verified the hypothesis of niche complementary effect, biomass ratio effect and vegetation quantity effect. The explanatory variables together explained the change of 13% forest carbon stock and 36% forest carbon increment.

  Conclusion  Carbon storage and carbon increment are important reflection and direct embodiment of carbon sink function of forest ecosystem. This study has revealed the mechanism of the relationship between biodiversity and forest carbon sink function to a certain extent, indicating that the relationship pattern between biodiversity and carbon sink function in broadleaved Korean pine forest is the result of multiple ecological mechanisms. The research results can provide a theoretical basis for the realization of “carbon fixation and sink enhancement” and “simultaneous enhancement of biodiversity and ecosystem functions” of broadleaved Korean pine forests.