Neither mycorrhizal inoculation nor atmospheric CO concentration has strong effects on pea root production and root loss.

•  Root responses to elevated CO concentrations, where nutrient demand was expected to be higher than at ambient CO , and possible interactions with mycorrhizal symbionts are reported for pea (Pisum sativum). These are important below-ground components affecting carbon flow into the soil. •  A video-minirhizotron system was used to study root growth in pot-grown mycorrhizal (inoculated with Glomus caledonium) and nonmycorrhizal pea plants at ambient or elevated CO concentrations over 9 wk. Analyses were made of root length changes, cohort size and survivorship. •  Root length production at ambient, but not at elevated CO , was higher in nonmycorrhizal than in mycorrhizal plants from week 4-7. Root loss began at week 5, peaking 2 wk later with 40-50% loss of the root length produced by week 8. The decline in root production and increase in root loss coincided with the onset of flowering. •  Neither mycorrhizal inoculation nor CO concentration has a strong effect on pea root production and root loss, although mycorrhizal infection has a greater effect than CO .