The symbiotic relationships between trees and different mycorrhizal fungi affect the biodiversity-ecosystem functioning relationships within forest communities, particularly across different strata from the understorey to the overstorey. However, current research on this relationship has not yet reached a definitive conclusion. In this study, we used regression analyses and structural equation modelling based on a 9-ha mixed broadleaved-Korean pine (Pinus koraiensis) forest plot to explore the effects of different types of mycorrhizal fungi (arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi) on the relationship between tree species diversity and productivity. The study found that the dominance and productivity of AM species increased in the understorey with increasing soil nutrients, whereas the productivity of EM species declined despite increasing diversity. In the overstorey, the productivity of AM species continued to increase with increasing soil nutrients, while that of EM species decreased due to increased competition. As for diversity-productivity relationships (DPRs), in the understorey, both AM and EM tree species demonstrated a positive DPR, suggesting the presence of the niche complementarity effect. In the overstorey, AM species continue to exhibit positive DPR due to their competitive advantage in nutrient-rich environments. In contrast, EM species exhibit negative DPR due to increased competition or less efficient resource use. Additionally, slope influenced forest productivity indirectly by altering the accumulation and distribution of soil nutrients, thereby affecting species distribution and growth conditions. This indirect effect highlights the potential negative impact of slope on soil nutrients within forest ecosystems, as well as its influence on the relationships between biodiversity and ecosystem functions. The study reveals how AM and EM trees influence forest productivity through distinct adaptability and competitive strategies across different forest strata, with a particular emphasis on the strata-dependent effects of mycorrhizal association on DPRs. This finding offers a new perspective on how mycorrhizal types modulate the complex relationships between biodiversity and ecosystem functions across various strata in temperate forests.

The resorption of nutrients by plants before litter fall and the mineralization of nutrients from plant litter by soil processes are both important pathways supporting primary productivity. While the positive relationship between plant biodiversity and primary productivity is widely accepted for natural ecosystems, the roles of nutrient resorption and mineralization in mediating that relationship remains largely unknown. Here, we quantified the relative importance of nitrogen (N) resorption and N mineralization in driving plant community N investment and the correlation between species diversity and community productivity along an N-limited successional chronosequence of the mixed broadleaved–Korean pine (Pinus koraiensis) forest in northeastern China. Leaf N resorption efficiency (NRE) at the community level increased significantly along the successional chronosequence, whereas litter N mineralization rate decreased significantly. Leaf NRE was more important than litter N mineralization rate in driving the diversity–productivity relationship. However, higher leaf NRE led to less N mineralization as succession progressed along the chronosequence. Our results highlight the importance of the N resorption pathway rather than the N mineralization pathway for forest N acquisition with community succession, and they provide mechanistic insights into the positive effects of biodiversity on ecosystem functioning. In future forest management practices, we recommend appropriate application of N fertilizer to mitigate the adverse effects of N-poor soil on seedling regeneration during late succession and thus maintain the sustainable development of temperate forest ecosystems.