Species-specific effects of elevated CO2 on resource allocation in Plantago maritima and Armeria maritima

We investigated the effects of increased atmospheric CO2 on the biomass, photosynthesis, protein and phenolic concentrations and content of Plantago maritima and Armeria maritima. This enabled us to test the protein competition model (PCM) for predicting C allocation to phenolics. Three contrasting responses to elevated CO2 (600 μmol CO2 mol−1) between the two study species were observed. (1) In P. maritima, plant biomass increased and the maximum carboxylation rate of Rubisco (Vc,max) was decreased. However, in A. maritima, shoot biomass decreased and the Vc,max of Rubisco was unchanged. (2) The total phenolic content increased in P. maritima but decreased in A. maritima. (3) Protein concentrations and content decreased in P. maritima and root protein concentrations and content increased in A. maritima. We conclude that C and N allocation to phenolics and proteins is species- and organ-specific and the PCM predictions were correct when phenolics and proteins were expressed on a per plant content basis.