EFFECTS OF LOW-CONCENTRATION SULFUR-DIOXIDE FUMIGATION AND VESICULAR ARBUSCULAR MYCORRHIZAS ON C-14 PARTITIONING IN PHLEUM-PRATENSE L

The effect of long-term low-concentration (0.04 - 0.065-mu-l l-1) exposure to sulphur dioxide (SO2) on assimilate partitioning in Phleum pratense colonized by vesicular-arbuscular (VA) mycorrhizal fungi from field soil was examined by supplying leaves with (CO2)-C-14. Seedlings were grown and exposed to SO2 for six weeks and then pulsed with (CO2)-C-14 for 15 min. The distribution of the C-14 was analysed after a 12 h chase. SO2 fumigation had little effect on plant dry matter production, however, it had significant effects on the assimilation of (CO2)-C-14. Plants colonized by VA mycorrhizal fungi, both fumigated and controls, had a greater percentage of the total incorporated C-14 in the roots, a significantly lower percentage of the total as C-14-labelled soluble carbohydrates in the shoots, and a greater percentage of the total as C-14-labelled amino- and organic acids in the shoots and roots than non-mycorrhizal plants. SO2 exposure reduced root length, root length colonized by VA mycorrhizal fungi, and the length of root infected with arbuscules. It appeared that colonization by VA mycorrhizal fungi in field soil had an overriding effect on carbon assimilation, use, and translocation in the host, and these probably affect host sensitivity to SO2 exposure.