Different plant species have differential response to increases in atmospheric CO2 concentration (Ca). This differential response could lead to quantitative changes in competition among species and community composition, with flow-on effects for ecosystem function. However, there has been little theoretical analysis of how Ca levels will affect plant competition, and there is currently no consensus regarding how the composition of plant communities might change. Thus, we investigated theoretically how plant competition might change under high Ca.
We applied two theories of competition; resource use theory and resource partitioning theory to a plant carbon and nitrogen cycling model and investigated the outcome of plant competition under low and high Ca.
Results/Conclusions
Both theories predicted that the most important traits for winners in the trait-wise case are high carbon use efficiency, low ratio of root N: C to leaf N: C and high carboxylation rate per unit leaf nitrogen. Resource use theory makes the novel prediction that elevated Ca is unlikely to change species dominance in competition. In contrast, resource partitioning theory predicts that elevated Ca may decrease the dominance ratio of the winning species. Collectively, both theories suggest that elevated Cawill favor coexistence.
We concluded that the logic of plant C: N relations suggest that species diversity should increase with elevated Ca. This novel theory-based hypothesis has potential to help guide design and interpretation of elevated Caexperiments.