Decreasing relatedness among mycorrhizal fungi in a shared plant network
increases fungal network size but not plant benefit
Abstract
Relatives are expected to cooperate more and compete less. In symbiotic
partnerships, hosts may benefit from interacting with highly-related
symbionts because there is less conflict. This has been difficult to
test empirically. We used the arbuscular mycorrhizal symbiosis to study
the effects of fungal relatedness on host and fungal benefits, creating
fungal networks varying in relatedness (self vs. non-self) between two
host plants, in both soil and in-vitro systems. To determine how fungal
relatedness affected overall transfer of nutrients to host roots, we
fluorescently tagged phosphorus and quantified resource distribution. We
imaged fungal networks, and related fractal dimension to fungal growth
strategies. We found that decreased relatedness was associated with
increased fungal growth and complexity, lower transport of nutrients
across the fungal network, and lower plant benefit, likely an outcome of
increased fungal competition. More generally, we demonstrate how
relatedness among symbionts can mediate the overall benefits of
symbiotic partnerships.