Multiple mechanisms drive biodiversity-ecosystem service multifunctionality but the dominant one depends on the level of multifunctionality for natural forests in northeast China

•Mass ratio effect, ecological niche complementarity and green soup hypotheses simultaneously contributed to biodiversity-multifunctionality relationship, but dominant one varied with the threshold (multifunctionality level).•Generally, green soup hypothesis was the dominant mechanism behind biodiversity-multifunctionality relationship for natural temperate forests in northeast China.•Attention should be paid to maintaining high functional and structural diversity and large biomass to maximize the multifunctionality.