Trading on the arbuscular mycorrhiza market: from arbuscules to common mycorrhizal networks

Abstract

Summary Arbuscular mycorrhiza (AM) symbiosis occurs between obligate biotrophic fungi of the phylum Glomeromycota and most land plants. The exchange of nutrients between host plants and AM fungi (AMF) is presumed to be the main benefit for the two symbiotic partners. In this review article, we outline the current concepts of nutrient exchanges within this symbiosis (mechanisms and regulation). First, we focus on phosphorus and nitrogen transfer from the fungal partner to the host plant, and on the reciprocal transfer of carbon compounds, with a highlight on a possible interplay between nitrogen and phosphorus nutrition during AM symbiosis. We further discuss potential mechanisms of regulation of these nutrient exchanges linked to membrane dynamics. The review finally addresses the common mycorrhizal networks formed AMF, which interconnect plants from similar and/or different species. Finally the best way to integrate this knowledge and the ensuing potential benefits of AM into sustainable agriculture is discussed.

Dual‐mycorrhizal plants: their ecology and relevance

“…We suggest that the mechanisms underlying mycorrhizal switching due to soil nutrient availability involve the following: first, the ability of EM fungi to access organic P, which accumulates in older soil, via excretion of phosphatases; second, the ability of EM fungi to scavenge more effectively and at further distances from the host roots compared with AM fungi; and third, the host plant's ability to control the level of AM fungal colonization and/or arbuscule development depending on nutrient requirements (Wipf et al, 2019).…”

Discreet heterotrophs: green plants that receive fungal carbon through Paris‐type arbuscular mycorrhiza

“…In the Arum-morphotype, greatly branched hyphal structures (arbuscules) develop within root cortical cells while sparsely branched hyphae run in the intercellular spaces along cell files (Gallaud, 1905;Dickson et al, 2007). Arbuscules presumably are the site of mineral nutrient fluxes from fungus to plant, and together with intercellular hyphae are also involved in photosynthate transfer from plant to fungus (Smith & Smith, 1997;Dickson et al, 2007;Wipf et al, 2019). This morphotype is frequent among agricultural plants (Dickson et al, 2007).…”

“…A selective advantage is suggested for plant control over morphotype establishment (Dickson, 2004;Dickson et al, 2007). However, the process of carbon transfer from fungi to plants is yet not completely clear (Dickson et al, 2007;Wipf et al, 2019). Interestingly, the 15 N enrichment of P. quadrifolia, partially mycoheterotrophic Gentianaceae (Cameron & Bolin, 2010) and Burmanniaceae (Bolin et al, 2017) as well as fully mycoheterotrophic plants on AM fungi (Merckx et al, 2010;Courty et al, 2011;Hynson et al, 2013) appears to be considerably lower than for mycoheterotrophic plants associated with fungi simultaneously forming ectomycorrhizas with neighboring forest trees (Hynson et al, 2016).…”

Imbalanced Regulation of Fungal Nutrient Transports According to Phosphate Availability in a Symbiocosm Formed by Poplar, Sorghum, and Rhizophagus irregularis

“…The extraradical mycelium (ERM) of the AM fungi engaged in such a network is able to acquire nutrients that are out of reach or not accessible to the plant partners. For a given plant, this makes the mycorrhizal uptake pathway often more effective than the direct uptake pathway (Wipf et al, 2019). The nutrients taken up by the ERM are transported to the hyphal network inside the host root via the intraradical mycelium (IRM), which forms highly branched tree-like structures (arbuscules) inside the root cortical cells.…”

“…The expression of transporters is regulated by nutrient availability. In this way, a steady and efficient translocation of nutrients adapted to given environmental conditions can be guaranteed (Smith and Smith, 2011;Courty et al, 2015;Garcia et al, 2016;Wipf et al, 2019).…”