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

Abstract

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 (15) N 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 (15) N, 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 (15) N 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.

Direct evidence for modulation of photosynthesis by an arbuscular mycorrhiza‐induced carbon sink strength

“…Our model system with limited space for sink adjustments did not allow us to explore other mechanisms for new sink development in both symbionts that may replace the sink strength lost after mycelium excision but demonstrated the importance of the mycorrhizal C sink strength. The strength of source–sink gradients had been demonstrated mainly in plants connected to ERM mycelium networks where the sink strength of some plants could affect the development of others by controlling the flow of C and mineral nutrients (Waters & Borowicz, ; Walder et al ., ; Merrild et al ., ; Fellbaum et al ., ; Weremijewicz et al ., ). Research on resource biological markets linking above‐ and belowground flows between plants and mycorrhizal fungi is rapidly expanding.…”

Fungal loop transfer of nitrogen depends on biocrust constituents and nitrogen form

“…In biological networks, the magnitude and direction of resource transfer in fungi is predominantly thought to be influenced by the physiological source-sink gradients created by individual plants (Fellbaum et al, 2014) or between plants (Weremijewicz et al, 2016). However, fungi may prove themselves to be more than just passive conduits by exerting control over resources due to their own source-sink resource needs (Simard and Durall, 2004).…”

Aphid infestation in the phyllosphere affects primary metabolic profiles in the arbuscular mycorrhizal hyphosphere

“…Through these AM underground networks, plants can interact with each other by exchanging nutrients, thereby influencing plant growth 19 , 20 . Several reports have focused on the possibility of unequal nutrient transfer inside these networks, which would increase competition between plants 21 , 22 by shifting carbon into roots of neighbouring plants via mycelial networks, where the shift may be skewed towards one of the involved plant species 23 . This shift has been postulated to be dependent on the functional compatibility of the AM genotype and its host plants 24 .…”