Fungal nutrient allocation in common mycorrhizal networks is regulated by the carbon source strength of individual host plants

Abstract

SummaryCommon mycorrhizal networks (CMNs) of arbuscular mycorrhizal (AM) fungi in the soil simultaneously provide multiple host plants with nutrients, but the mechanisms by which the nutrient transport to individual host plants within one CMN is controlled are unknown.Using radioactive and stable isotopes, we followed the transport of phosphorus (P) and nitrogen (N) in the CMNs of two fungal species to plants that differed in their carbon (C) source strength, and correlated the transport to the expression of mycorrhiza-inducible plant P (MtPt4) and ammonium (1723.m00046) transporters in mycorrhizal roots.AM fungi discriminated between host plants that shared a CMN and preferentially allocated nutrients to high-quality (nonshaded) hosts. However, the fungus also supplied low-quality (shaded) hosts with nutrients and maintained a high colonization rate in these plants. Fungal P transport was correlated to the expression of MtPt4. The expression of the putative ammonium transporter 1723.m00046 was dependent on the fungal nutrient supply and was induced when the CMN had access to N.Biological market theory has emerged as a tool with which the strategic investment of competing partners in trading networks can be studied. Our work demonstrates how fungal partners are able to retain bargaining power, despite being obligately dependent on their hosts.

Role of Arbuscular Mycorrhizal Fungi in the Nitrogen Uptake of Plants: Current Knowledge and Research Gaps

“…Some studies have demonstrated that the carbon supply of the host acts as an important trigger for P and N transport in the AM symbiosis [10,12,75]. However, there are also other reports in which the carbon to nutrient resource exchange was not directly correlated [13].…”

“…Recent results demonstrated that both P and N are important determinants for the AM symbiosis and that the colonization of the plant host is controlled by feedback mechanisms between both nutrients [12]. For example, both, P and N starvation of the plant induce a nutrient stress transcriptome that is favorable for AM colonization.…”

“…The synchronization of these processes suggests that Arg plays an important role in the N translocation from the ERM to the IRM [50,74,121]. The C supply of the host plant plays a significant role in the regulation of these processes [12,75]. An increase in the C supply from the host plant led to an up-regulation of genes that are involved in Arg biosynthesis (AL, ASS, CPS), but to a down-regulation of a fungal urease (URE) in the ERM [75].…”

“…These many-to-many interactions allow both partners in the symbiosis to choose among multiple trading partners but also force both partners to compete with other partners for nutrient or carbon resources [12,13]. CMNs play a key role for the long distance transport of nutrients, water, stress chemicals and allelochemicals and allow the interconnected host plants to "communicate" with other plants within their CMN [14][15][16][17][18].…”

Regulation of plants' phosphate uptake in common mycorrhizal networks: Role of intraradical fungal phosphate transporters

“…It is generally accepted that some plants and AMF are able to reduce resource transfer to symbiotic partners, when not receiving a "satisfying" benefit in return. 13,14 In the -1 a) was used as the reference transcript. Mycorrhizal acquisition of inorganic phosphate of sorghum was estimated based on uptake of labeled phosphorus only available for AM fungi.…”