Community diversity and composition affect ecosystem multifunctionality across environmental gradients in boreal and temperate forests

Aim: Biodiversity is known to affect ecosystem functioning, and environmental stress may influence the relationships between biodiversity and ecosystem functions (BEF). However, it is still unknown how the relationship between biodiversity and ecosystem multifunctionality (BEMF) varies with the environment at regional scale. We aimed to explore the change of BEMF relationship across environmental gradients in boreal and temperate forest ecosystems, and to identify the main impact mechanisms on EMF. Methods: Based on a data set collected in Northeastern China, we quantified EMF by calculating the average of six individual functions, defined species richness and functional diversity as community diversity, and defined the community-weighted means of functional traits as functional composition. We used multifactorial linear regression to assess the effect of biodiversity indices across environmental gradients on BEMF, and used structural equation models to identify the relationships among impact factors and EMF. Results: Community diversity and functional composition, as well as their interactions with environmental gradients, were jointly influencing the EMF. In the boreal forests, functional composition was the dominant driver of EMF. In the temperate forests, community diversity became the dominant factor impacting EMF. Main conclusions: The results imply that BEMF relationship changes with environmental conditions. EMF is mainly influenced by the community functional traits of the dominant species (mass ratio effect) in the boreal forests. In the temperate forests, greater community diversity leads to greater resource utilization and thus greater EMF (niche complementarity effect).