Effects of elevated carbon dioxide and arbuscular mycorrhizal infection on Trifolium repens

Trifolium repens L. cv. aran was grown for 58 d at ambient (350 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) atmospheric CO2, with and without the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerd. St Trappe cv. YV. Plant biomass, mycorrhizal infection, non-structural carbohydrates, C, N and P content were examined. Elevated CO2 (a) significantly increased above- and below-ground biomass, (b) decreased specific leaf area and specific root length, (c) decreased tissue %N and increased the C:N ratio, and (d) significantly increased total non-structural carbohydrates. Inoculating T. repens with Glomus mosseae (a) significantly increased above- and below-ground biomass, (b) increased the total root length and total leaf area, and (c) significantly decreased tissue %P. Evidence of an increased influence of mycorhiza on the P nutrition of T. repens at elevated CO2 was found in the 22% increase in leaf total P (P less than or equal to 0.05) of mycorrhizal plants grown at elevated CO2 compared with nonmycorrhizal plants. No significant interactions were found between CO2 and mycorrhiza treatments. The proportion of T. repens root length colonized by Glomus mosseae was not affected by CO2 concentration. The percentage mycorrhizal infection was 29% at ambient CO2 and 35% at elevated CO2. However, exposure to elevated CO2 significantly increased the total mycorrhizal root length from 3.4 to 6.1 m per plant. The results show little evidence that the role of arbuscular mycorrhiza in the growth and nutrition of T. repens would increase if atmospheric CO2 were to increase as predicted.