Seventeen Root Traits Altered by Atmospheric CO2 Enrichment
Nie, M., Lu, M., Bell, J., Raut, S. and Pendall, E. 2013. Altered root traits due to elevated CO2: a meta-analysis. Global Ecology and Biogeography 22: 1095-1105.
Nie et al. achieved their goal by conducting a meta-analysis of the effects of elevated CO2 on "17 variables associated with root morphology, biomass size and distribution, carbon and nitrogen concentrations and pools, turnover and fungal colonization from 110 published studies," where ambient CO2 concentrations ranged from 340 to 380 ppm and elevated concentrations from 540 to 750 ppm. Based on that analysis, the five U.S. researchers report that elevated CO2 increased average root length (+26.0%), root diameter (+8.4%), coarse root biomass (+25.3%), and root:shoot ratio (+8.5%), but that it decreased the proportion of roots in the topsoil (-8.4%), which suggests, however, that "plants expand rooting systems" in CO2-enriched air. In addition, they indicate that elevated CO2 decreased root nitrogen (N) concentration (-7.1%), but did not affect root carbon (C) content, and that it thus increased the root C:N ratio (+7.8%). They also indicate that root C pools (+29.3%) increased disproportionately relative to root N pools (+9.4%) under elevated CO2, and that "functional traits were also strongly affected by elevated CO2, which increased respiration (+58.9%), rhizodeposition (+37.9%) and fungal colonization (+3.3%)."
In summing up their findings, Nie et al. state "these results suggest that elevated CO2 promoted root morphological development, root system expansion and carbon input to soils, implying that the sensitive responses of root morphology and function to elevated CO2 would increase long-term belowground carbon sequestration."