Plant community assembly processes shape the composition and abundances of species, and encompass functional traits and resource acquisition strategy of species, biotic interactions and abiotic filtering. Hence, an understanding of these complex processes requires disentangling the effects of multiple factors influencing plant community assembly. In this thesis, I investigated fine root trait associations with soil microorganisms, the resulting feedback effects from those interactions (i.e., plant-soil feedbacks), plant-plant interactions under warming, and the effects of temperature on fine root traits of plant communities in the Swedish sub-arctic tundra.

Here, the chemical root economics spectrum (i.e., tradeoff between acquisitive and conservative strategies) predicted the abundance of broad microbial groups, whereas individual fine root traits were associated with the relative abundances of fungal taxa. It also explained plant-soil feedback, with acquisitive trait values resulting in negative feedbacks. In addition, plant-plant interactions were altered under warming, but this was not related to resource-acquisition strategy. Further, community-level root trait responses to temperature were not necessarily related to root resource investment strategy. 

Taken together, this thesis shows the importance of fine root traits for understanding plant community responses to global change. This has implications for plant community assembly, as well as carbon and nutrient cycling in a future warmer sub-arctic tundra.