Carbon gain, allocation, and storage in rhizomes in response to elevated CO2 and fertilization in an invasive perennial C3 grass, Phalaris arundinacea

Background/Question/Methods

Reed canary grass (Phalaris arundinacea L.) is a fast-growing, perennial, rhizomatous, C₃ grass considered as a model invasive species for its aggressive weedy behavior in many parts of the world, including the United States. Conversely, the same traits make it a candidate for bioenergy feedstock elsewhere. We tested the hypothesis that elevated CO₂ and fertilization promote the growth of this fructan accumulating cool-season grass with little or no photosynthetic down-regulation. We also tested whether elevated CO₂ and nutrient availability alters fructan storage in rhizomes. Plants were grown at ambient or elevated (+320 μmol mol^-1) CO₂, and fertilized using full- or 1/8^th-strength Hoagland’s solution. The experiment was repeated in summer and fall. We investigated leaf photosynthesis, whole-plant water use, biomass allocation, and nitrogen and carbon storage in rhizomes. 

Results/Conclusions

Elevated CO₂ enhanced light-saturated net CO₂ assimilation (A_max) by 61%. It doubled whole-plant, stem, and root biomass in summer. Plants grown in elevated CO₂ assimilated carbon more efficiently at higher CO₂ concentrations than those grown in ambient CO₂. This response indicates an acclamatory shift for enhanced carbon gain under elevated CO₂. In fall, fructan in rhizomes increased from 5.64% under ambient CO₂ to 7.76% under elevated CO₂ (P=0.054). Our results support that elevated CO₂ combined with sufficient nutrients is likely to enhance carbon gain and growth of the species with little down-regulation and to increase productivity and competitiveness of Phalaris arundinacea in summer. Elevated CO₂ is also likely to enhance long-term fructan storage in rhizomes in fall. This response may benefit overwintering and early sprouting.