Effects of CO₂ Enrichment on the Growth of Arabidopsis thaliana under the Constantly Nitrogen-limited Conditions

Abstract

Assimilation pathways of CO₂ and nitrogen are closely related to each other. It has been observed that elevated CO₂ leads to stimulation of growth under nitrogen-sufficient conditions. However, effects of elevated CO₂ on the growth under nitrogen-limited conditions are still unclear because of difficulties in maintaining such conditions in experiments. Here, we kept Arabidopsis thaliana under nitrogen-limited conditions by using the mutant with reduced nitrate uptake activities and examined the effects of elevated CO₂. Under the nitrogen-sufficient conditions (i.e., in the presence of ammonium), both the wild type and the mutant exhibited ~2-fold increase in biomass when CO₂ concentration was increased from 280 to 780 ppm. Similar effects of elevated CO₂ were observed for the wild type growing on the medium containing 15 mM nitrate as sole nitrogen source. In contrast, the mutant growing on the nitrate-containing medium showed unchanged shoot biomass regardless of elevated CO₂, whereas root biomass was increased in response to elevated CO₂. This symptom is considered to be a specific response to elevated CO₂ in plants kept under the nitrogen-limited condition.