When ranges collide: evolutionary history, phylogenetic community interactions, global change factors, and range size differentially affect plant productivity

Humans are extensively changing the global environment, both by altering abiotic conditions through increases in carbon dioxide (CO₂) and reactive nitrogen (N), and by driving patterns of extinctions and introductions that shift community composition and affect the biotic environment. Evolutionary history may play an important role in determining plant responses to global change, if evolution has selected for certain traits (biomass, allocation strategies, range size, etc.) that determine plant responses to rising CO₂ and N. Additionally, the evolutionary history of interacting plants (i.e. phylogenetic relationships within plant communities) may determine how plants respond to global change, as closely related species might be expected to compete more for limiting resources than distantly related species. Using 26 Australian eucalypt species in two subgenera (Eucalyptus and Symphyomyrtus) of the genus Eucalyptus, we conducted the first experiment, to our knowledge, that simultaneously integrated contemporary range size, phylogenetic identity, phylogenetic similarity, and global change factors (CO₂ and N). We showed that plant biomass responded to two three-way interactions: (1) subgenus identity, N fertilization, and phylogenetic similarity and (2) subgenus identity, CO₂ enrichment, and N fertilization. Our results indicate that eco-evolutionary dynamics are linked in diverse and non-intuitive ways where evolutionary history (i.e. subgenus-level differences) mediates how plant productivity responds to resource manipulation, and that the nature of this response depends on the phylogenetic composition of plant communities. Overall, these findings have significant implications for how we understand the ecosystem-level consequences of climate change.