Effects of Vesicular-Arbuscular Mycorrhiza on ¹⁴c and ¹⁵n Distribution in Nodulated Fababeans

A two-compartment growth chamber in which the aboveground plant materials were exposed to 14 CO 2 and the belowground portion was exposed to 15 N 2 under normal atmospheric pressure was designed for carbon and nitrogen transfer studies. Vicia faba infected with vesicular-arbuscular fungus Glomus mossae and non-mycorrhizal plants fixed similar quantities of N 2 at an age of 6½ wk. Approximately 0.10 mg N was fixed∙g −1 dry plant materials∙day −1 and 40 mg C∙g −1 dry matter day −1 were synthesized by mycorrhizal and non-mycorrhizal fababeans during 48 h exposure to 14 CO 2 at 6½ wk with no apparent difference in yield of dry matter. The non-mycorrhizal plants transferred 37% of the fixed 14 C beneath ground. The mycorrhizal ones transferred 47% of the fixed 14 C beneath ground. Most of the difference could be accounted for in the belowground respiration. The 14 CO 2 produced by root-microbial systems of the mycorrhizal fababeans was twice as great as that of the nonmycorrhizal; both contained active rhizobium.