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

Mayra E. Gavito*, Iver Jakobsen, Teis Nørgaard Mikkelsen, Francisco Mora

*Corresponding author for this work

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It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and down-regulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence. We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily. Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10-40%) decline in photosynthetic rates that lasted from 30 min to several hours in plants that were well nourished and hydrated and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700 ppm) atmospheric CO2 . This is first direct experimental evidence for the carbon sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source-sink relations and may have strong implications in large-scale assessments and modelling of plant photosynthesis. This article is protected by copyright. All rights reserved.
Original languageEnglish
JournalNew Phytologist
Issue number2
Pages (from-to)896-907
Publication statusPublished - 2019


  • carbon (C) assimilation
  • elevated CO2
  • gas-exchange
  • mycorrhiza
  • source-sink relations

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