Carbon gain, allocation and storage in rhizomes in response to elevated atmospheric carbon dioxide and nutrient supply in a perennial C-3 grass, Phalaris arundinacea

Reed canary grass (Phalaris arundinacea L.) is a fast-growing, perennial, rhizomatous C-3 grass considered as a model invasive species for its aggressive behaviour. The same traits make it a candidate for bioenergy feedstock. We tested the following hypotheses: (1) elevated atmospheric [CO2] and nutrient supply enhance photosynthetic carbon acquisition of this fructan-accumulating grass with little or no photosynthetic downregulation; (2) elevated [CO2] promotes carbon allocation to growth when nutrients are sufficient and to fructan storage in rhizomes when nutrients are low. Plants were grown at ambient or elevated (+320 mu mol mol(-1)) [CO2], and fertilised using full or one-eighth strength modified Hoagland solution. We investigated leaf photosynthesis, whole-plant water use, biomass allocation, and nitrogen and carbon storage in rhizomes. Elevated [CO2] enhanced light-saturated net CO2 assimilation by 61%. It doubled whole-plant, stem and root biomass in summer. Plants grown in elevated [CO2] had a greater rate of CO2 assimilation at higher [CO2], indicating a shift in photosynthetic apparatus for enhanced carbon gain under elevated [CO2]. The majority of belowground biomass was allocated to rhizomes for storage rather than to roots in both seasons. In autumn, elevated [CO2] increased fructan concentration in rhizomes from 8.1 to 11.7% of biomass when nutrients were low (P = 0.023). Our results suggest that elevated [CO2] combined with sufficient nutrients is likely to enhance carbon gain and growth of P. arundinacea, and to increase its productivity and competitiveness in summer. Elevated [CO2] is likely to enhance long-term fructan storage in rhizomes, which may benefit overwintering and vegetative spread.