Experimental and observational studies have elucidated that an amalgamation of biotic (e.g., biodiversity, large trees) and abiotic factors (e.g., climate, soil) jointly determine tree aboveground carbon stock within forest ecosystems. Yet, a pivotal factor potentially influencing these carbon repositories might be the specific tree mycorrhizal associations, especially given that ectomycorrhizal (EM) tree species frequently comprise more large-sized trees, translating to an augmented carbon reserve, as opposed to arbuscular mycorrhizal (AM) counterpart. However, how biotic and abiotic factors determine forest carbon through regulating AM vs. EM tree carbon stock is still elusive across large regions. Here, we examined a forest inventory data consisting of over 90,000 trees from 631 forest plots (30m × 30m each). Our objective was to explore how biodiversity (i.e., species diversity and ecological uniqueness), large trees (top 1% tree diameters), and environmental factors (e.g., climate and soil nutrients) differently regulate AM and EM, and thus, total tree aboveground carbon stock of temperate forests in northeast China. Our findings illuminated that large trees had consistent enhancement effect on AM and EM tree carbon repositories. However, the effects of biodiversity and environmental factors on carbon stock were opposite between AM and EM trees. Specifically, the two components of biodiversity were positively associated with AM tree carbon stock while negatively associated with EM tree carbon stock. Environment heterogeneity (i.e. mean annual temperature and soil nutrients) also exhibited contrasting impacts on AM and EM tree carbon stock. Consequently, when integrating AM and EM tree carbon stock into total carbon stock, the consistent effect of large trees on AM vs. EM trees was strengthened and most important, while the opposite effect of biodiversity or environment factors was diluted. In summary, this study emphasized a mycorrhizal viewpoint to better understand the determinants of overarching aboveground carbon profile across regional forests.

Association is the basic unit of plant community classification. Exploring the distribution of plant associations can help improve the understanding of biodiversity conservation. Different associations depend on different habitats. Studying the association level is significant for ecological restoration, regional ecological protection, regulating the ecological balance, and maintaining biodiversity. However, previous studies have focused only on the suitable distribution areas of species and not on the distribution of plant associations. Larix gmelinii is a sensitive and abundant species spread in the southern margin of Eurasian boreal forests, and its distribution is closely related to permafrost. In this study, 420 original plots of L. gmelinii forests were investigated. We used Maxent model and ArcGIS software to project the potential geographical distribution of L. gmelinii associations in the future (by 2050 and 2070) according to the climate scenarios RCP 2.6, RCP 4.5, and RCP 8.5. The causes for the changes in spatial distribution were analyzed using multinomial logistic regression analysis. The results revealed that temperature is the most important factor affecting the distribution of L. gmelinii forests and most of its associations under different climate scenarios. Further, the suitable areas for each association type are shrinking by varying degrees, especially due to habitat loss at high altitudes in special terrains. For different L. gmelinii associations, management measures should also be different based on the different site conditions, composition structure, growth, development, and renewal succession trends. Furthermore, subsequent research should consider data on biological factors to obtain more accurate prediction results.