Co-limitation of plant phylogenetic community structure by elevated CO2 and nitrogen deposition in an alpine grassland

Background/Question/Methods , Global environmental changes caused by human activities, such as elevated atmospheric CO₂ concentrations and N deposition, are strongly influencing all aspects of terrestrial ecosystem. The combined impact of co-occurring global changes on plant community phylogenetic structure and the underlying mechanisms, however, are poorly understood. We examined plant community phylogenetic structure responses in an alpine grassland on the Tibetan Plateau to manipulations of two environmental changes, singly and in combination: elevated CO₂ and nitrogen deposition.

Results/Conclusions , After 4 years, N addition (aN) and elevated CO₂ (eCO₂) singly did not alter plant species richness, whereas aN plus eCO₂ treatment decreased species richness. Neither N addition nor elevated CO₂ influenced community phylogenetic structure, but aN plus eCO₂ altered it, driving communities from phylogenetic overdispersion to clustering. The observed alteration in community phylogenetic structure towards clustering under aN plus eCO₂ treatment was associated with the extinction of species that were closely related to the resident species. Our study illustrates that plant species richness and community phylogenetic structure display synergistic response to elevated CO₂ and N addition.Our findings highlight the importance of synergistic interactions between N availability and atmospheric CO₂ in regulating community phylogenetic structure, and point to the need for future studies that address the co-limitation of global environmental changes on plant community structure.