Some plant species have been shown to uptake and fix rhizospheric carbon dioxide (CO₂) in their root tissues. This process is associated with supplying the necessary carbon skeletons for assimilation of nitrogen (specifically NH4) into amino acids, providing an important linkage between plant carbon and nitrogen cycles. Despite the potential impact of rhizospheric CO₂ fixation on plant metabolism, root carbon fixation remains poorly described in many ecologically important systems, including forest trees.  Here we present data on the effects of increased rhizospheric CO₂ on root metabolism in Populus deltoides, an emerging model agriforest species. 

Results/Conclusions

Application of bicarbonate (5-25mM) to the rooting zone of P. deltoides was found to significantly enhance root biomass accumulation (p<0.05) and the root to shoot ratio of young trees. Despite the increase in root biomass, shoot biomass accumulation was unaffected, and increasing concentrations of rhizospheric bicarbonate did not enhance overall leaf photosynthetic rates, suggesting the increase in root biomass accumulation was not a result of enhanced leaf-level CO₂ assimilation. Using a novel hydroponic system we present results exploring how root PEP-carboxylase activity, TCA cycle intermediates, and respiration rates are influenced by rhizospheric CO₂ concentration in roots of Populus deltoides. We discuss the implications of these results as it relates to the relationship between rhizospheric CO₂ concentration and plant-soil interactions, particularly as it relates to the relationship between root carbon fixation and nitrogen acquisition in Populus.