EFFECT OF CLIPPING, BENOMYL, AND GENET ON C-14 TRANSFER BETWEEN MYCORRHIZAL PLANTS

We examined how simulated herbivory, fungicide, and genet affect the magnitude and direction of net carbon transfer between paired mycorrhizal Lotus corniculatus. One plant in each pair was labeled with C-14, and C-14 levels in the unlabeled plant were quantified. Without fungicide, the roots of unlabeled plants received significantly more C-14 when the labeled partner was clipped than when the unlabeled plant was clipped, indicating that net carbon flow was away from clipped plants and toward unclipped plants. Because the specific activity of donor roots was unaffected by simulated herbivory, fungicide, and genet, significant differences in net carbon flow were not simply due to differences in C-14 uptake by labeled plants. Clipping did not affect carbon transfer between plants in trays treated with the fungicide benomyl, which probably reduced but did not eliminate VAM colonization. The three genets did not differ. The median C-14 levels of unlabeled root samples were only 1.2% the C-14 levels of labeled plants' roots and thus constituted a very small portion of their carbon budget. C-14 levels in stems of unlabeled plants were never above background, suggesting that the fungal symbiont retained most of the transferred carbon. Although clipping can affect net carbon flow, we failed to detect significant differences in the amount of C-14 leaking from the roots of clipped vs unclipped plants. This study suggests that grazed mycorrhizal plants are unlikely to gain significant amounts of carbohydrates from neighbors and may actually experience a net loss.