Carbon transfer between C3 and C4 plants linked by a common mycorrhizal network, quantified using stable carbon isotopes

Changes in the natural abundance of 13C were used to quantify carbon transfer between C3 and C4 plants in a common mycorrhizal network. Experiments using two mesh sizes to either prevent (0.45 μm) or allow (20 μm) mycorrhizal connections between Plantago lanceolata (C3) and Cynodon dactylon (C4) plants were run. Root and shoot samples were taken for δ13C determinations. ld not be assumed that all the pairs of plants were linked; therefore non-parametric statistical tests were used. In order to measure transfer between pairs of plants the shoot δ13C value was used as a reference and the deviation of the root δ13 C value from this as a measure of carbon transfer. As the C. dactylon root δ13 C value became more negative with the 20 μm mesh present, the root-shoot difference increased. In P. lanceolata both the root and shoot δ13C values became less negative but the root-shoot difference did increase gradually. When the root-shoot difference in C. dactylon was plotted against root δ13C value the relationship was ≈unity, suggesting that transferred carbon remained in the roots and fungal material did not move into the shoots. In P. lanceolata the results showed that the slope of the relationship between root-shoot difference and root δ13C value was ≈0.5. This suggests any transferred carbon moved into both the root and shoot material. ot-shoot difference can be used to estimate % carbon transfer. For individual C. dactylon plants the results varied from 0 to 41% with most values falling at 10% or below. It was not possible to calculate % transfer amounts for P. lanceolata. This range of variation could have important implications for plant interactions in communities.