Submitted to: New Phytologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/23/2014
Publication Date: 5/6/2014
Publication URL: http://handle.nal.usda.gov/10113/61885
Citation: Felllbaum, C.R., Mensah, J.A., Cloos, A.J., Strahan, G.D., Pfeffer, P., Kiers, T., Bucking, H. 2014. Fungal nutrient allocation in common mycorrhizal networks is regulated by the carbon source strength of individual host plants. New Phytologist. DOI:10.1111/nph.12827. Interpretive Summary: Multi-compartmented growing chambers (see below) were used to evaluate how carbon availability for the arbuscular mycorrhizal (AMF) fungus affects nutrient allocation in common mycelia networks. Nitrogen movement was evaluated in extracts derived from various compartments with different photosynthetic exposures. Quantitative PCR of genes involved in nitrogen and phosphorus transport was also used to evaluate the effect of shading on the expression of genes involved in N and P transport between the AMF arbuscule and the plant roots. This work represents an important break-through for studying symbiosis in living plants under uncontaminated conditions, as opposed to previous studies with model transformed roots or plants in uncontrolled environments. The results of this study can help us determine the best regimes to use to optimize the use of mycorrhizal inoculums.
Technical Abstract: • The common mycorrhizal networks (CMN) of arbuscular mycorrhizal (AM) fungi in the soil provide multiple host plants with nutrients, but the mechanisms by which the nutrient transport to individual host plants within one CMN is controlled, are currently unknown. • We followed by radioactive and stable isotope labeling the transport of phosphate (P) and nitrogen (N) by CMNs to Medicago plants, that differed in their photosynthetic capability and correlated the nutrient transport to the expression of plant P and ammonium transporters in the mycorrhizal interface. • AM fungi discriminated between host plants that shared a CMN and both AM fungi preferentially allocated nutrients to plants that were able to provide more benefit. Fungal P transport was correlated with the expression of MtPt4 in mycorrhizal roots. When the CMN had access to N, the putative ammonium transporter 1723.m00046 was induced, suggesting that this transporter plays a role in the N transport across the mycorrhizal interface. • Plants compete with other plants for limited resources and the carbon source strength plays a role in the fungal nutrient allocation within CMNs. However, AM fungi also transfer nutrients to low quality hosts to ensure a continuous carbon supply for their obligate biotrophic life style.