Functional diversity in arbuscular mycorrhizal (AM) symbioses: the contribution of the mycorrhizal P uptake pathway is not correlated with mycorrhizal responses in growth or total P uptake

Abstract

Summary• We investigated structural and functional diversity in arbuscular mycorrhizal (AM) symbioses involving three plant species and three AM fungi and measured contributions of the fungi to P uptake using compartmented pots and 33 P. The plant / fungus combinations varied in growth and P responses. Flax ( Linum usitatissimum ) responded positively to all fungi, and medic ( Medicago truncatula ) to Glomus caledonium and G. intraradices , but not Gigaspora rosea . Tomato ( Lycopersicon esculentum ) showed no positive responses.• Hyphal growth in soil was very low for Gi. rosea and high for both Glomus spp. Hyphal lengths in root + hyphal compartment (RHC) and hyphal compartment (HC) were similar for G. intraradices , but much higher in HC for G. caledonium .• Specific activities of 33 P in plants and soil indicated that fungal P uptake made substantial contributions to five plant/fungus combinations and significant contributions to a further two. G. intraradices delivered close to 100% of the P in all three plants. G. caledonium and Gi. rosea delivered less P. The amount was not related to colonisation or to growth or P responses.• We conclude that: AM colonisation can result in complete inactivation of the direct P uptake pathway via root hairs and epidermis; calculations of AM contributions to P uptake from total plant P will often be highly inaccurate; and lack of plant responsiveness does not mean that an AM fungus makes no contribution to P uptake.

Defense Related Phytohormones Regulation in Arbuscular Mycorrhizal Symbioses Depends on the Partner Genotypes

“…Despite the high promiscuity of AMF species capable of forming a successful symbiosis with most host plants, a high functional diversity among different combinations has been reported in terms of morphology, efficiency, and gene expression patterns of the symbiosis (Feddermann et al 2010). The two AMF species used in this study, Funneliformis mosseae and Rhizophagus irregularis, −formerly Glomus mosseae and Glomus intraradices, both within the Glomeraceae family (Krüger et al 2012)-are the most common AMF used in functional and biodiversity studies, and they are present across drastically different environments (Smith and Read 2008). A different level of mycorrhizal colonization was observed when comparing both fungi, R. irregularis being the most effective colonizer in the three host plants tomato, soybean, and maize.…”

“…The effective regulation of defense mechanisms upon recognition of the microbe relies on the phytohormones salicylic acid (SA), jasmonic acid (JA) and derivatives (JAs), ethylene (ET), and abscisic acid (ABA), which play central roles in coordinating plant responses . Among plant associations with beneficial microorganisms, arbuscular mycorrhizas (AM) are one of the most widespread, with a major impact on plant health and ecosystem dynamics (Smith and Read 2008). About 80 % of all land plants are able to form this mutualistic association with soil-borne fungi from the phylum Glomeromycota, known as arbuscular mycorrhizal fungi (AMF) (Smith and Read 2008).…”

“…Among plant associations with beneficial microorganisms, arbuscular mycorrhizas (AM) are one of the most widespread, with a major impact on plant health and ecosystem dynamics (Smith and Read 2008). About 80 % of all land plants are able to form this mutualistic association with soil-borne fungi from the phylum Glomeromycota, known as arbuscular mycorrhizal fungi (AMF) (Smith and Read 2008). They are obligate biotrophs that obtain carbohydrates from their host, while they improve mineral nutrition and water acquisition by the host plant (Parniske 2008).…”

“…Although AMF are considered non specific with respect to host range, there is evidence for certain "functional diversity". That is, both the plant and fungal genotypes determine the benefits of the interaction, some combinations being more efficient than others in terms of nutrition and/or stress resistance improvement (Cavagnaro et al 2001;Feddermann et al 2010;Pozo et al 2002;Smith et al 2004). The interaction requires a high degree of coordination between both partners, and bidirectional (plant and fungal) control assure a fair trade of resources between the symbionts (Kiers et al 2011).…”

Water management, rice varieties and mycorrhizal inoculation influence arsenic concentration and speciation in rice grains

“…Arbuscular mycorrhizal fungi (AMF) are ubiquitous symbionts for the majority of higher plants in the terrestrial ecosystems (Smith and Read 2008). It has been well documented that AMF may play an important role in protecting host plants against As contamination Liu et al 2005).…”