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Common mycorrhizal networks amplify competition by preferential mineral nutrient allocation to large host plants

Weremijewicz, Joanna, Sternberg, Leonel da Silveira Lobo O'Reilly, Janos, David P.
The new phytologist 2016 v.212 no.2 pp. 461-471
Andropogon gerardii, carbon, host plants, mycorrhizal fungi, nitrogen, nutrients, roots, shade, stable isotopes, vesicular arbuscular mycorrhizae
Arbuscular mycorrhizal (AM) fungi interconnect plants in common mycorrhizal networks (CMNs) which can amplify competition among neighbors. Amplified competition might result from the fungi supplying mineral nutrients preferentially to hosts that abundantly provide fixed carbon, as suggested by research with organ‐cultured roots. We examined whether CMNs supplied ¹⁵N preferentially to large, nonshaded, whole plants. We conducted an intraspecific target–neighbor pot experiment with Andropogon gerardii and several AM fungi in intact, severed or prevented CMNs. Neighbors were supplied ¹⁵N, and half of the target plants were shaded. Intact CMNs increased target dry weight (DW), intensified competition and increased size inequality. Shading decreased target weight, but shaded plants in intact CMNs had mycorrhizal colonization similar to that of sunlit plants. AM fungi in intact CMNs acquired ¹⁵N from the substrate of neighbors and preferentially allocated it to sunlit, large, target plants. Sunlit, intact CMN, target plants acquired as much as 27% of their nitrogen from the vicinity of their neighbors, but shaded targets did not. These results suggest that AM fungi in CMNs preferentially provide mineral nutrients to those conspecific host individuals best able to provide them with fixed carbon or representing the strongest sinks, thereby potentially amplifying asymmetric competition below ground.