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Fig. S1 False-colour digital autoradiographs of (a) Goodyera repens 72 h after exposure of its shoots to 14CO2 in a microcosm, and (b) the agar substrate on which the orchid roots rested, confirming negligible release of 14C as root exudate. An arrow indicates the location of the plant on the agar block before it was removed, and the colour scale shows the number of counts detected in pixel areas of 0.25 mm2 in a period of 60 min. The 14C labelling of three replicate plants took place before the mycorrhizal mycelium of the fungus established on the agar surface, but was otherwise identical to that described in Expt 3. This enabled the extent of 14 Crelease into the agar via root exudation to be distinguished from transfer through external mycelium (cf. Figs 5, 6). Partitioning of 14C assimilate within shoots, roots and into agar was quantified using sample oxidation, as described for Expt 3. Allocation of 14C into the agar was 0.3% of the total 14C assimilated, nearly an order of magnitude lower than the 2.6% assimilate found in the external mycelium in the earlier experiment, a difference that was significant (P = 0.03). The 14C partitioning between shoots and roots of plants with and without external mycorrhizal mycelia were almost identical and did not differ significantly between the two experiments (P > 0.05).

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NPH1767sm_FigS1.JPG861KSupporting info item