Multiple Arbuscular Mycorrhizal Fungal Consortia Enhance Yield and Fatty Acids of Medicago sativa: A Two-Year Field Study on Agronomic Traits and Tracing of Fungal Persistence

Abstract

Arbuscular mycorrhizal fungi are promoted as biofertilizers due to potential benefits in crop productivity, and macro- and microelement uptake. However, crop response to arbuscular mycorrhizal fungi (AMF) inoculation is context-dependent, and AMF diversity and field establishment and persistence of inoculants can greatly contribute to variation in outcomes. This study was designed to test the hypotheses that multiple and local AMF inoculants could enhance alfalfa yield and fatty acids (FA) compared to exotic isolates either single or in the mixture. We aimed also to verify the persistence of inoculated AMF, and which component of the AMF communities was the major driver of plant traits. Therefore, a field experiment of AMF inoculation of alfalfa (Medicago sativa L.) with three single foreign isolates, a mixture of the foreign isolates (FMix), and a highly diverse mixture of local AMF (LMix) was set up. We showed that AMF improved alfalfa yield (+ 68%), nutrient (+ 147% N content and + 182% P content in forage), and FA content (+ 105%). These positive effects persisted for at least 2 years post-inoculation and were associated with enhanced AMF abundance in roots. Consortia of AMF strains acted in synergy, and the mixture of foreign AMF isolates provided greater benefits compared to local consortia (+ 20% forage yield, + 36% forage N content, + 18% forage P content, + 20% total FA in forage). Foreign strains of Funneliformis mosseae and Rhizophagus irregularis persisted in the roots of alfalfa 2 years following inoculation, either as single inoculum or as a component of the mixture. Among inoculants, F. mosseae BEG12 and AZ225C and the FMix exerted a higher impact on the local AMF community compared with LMix and R. irregularis BEG141. Finally, the stimulation of the proliferation of a single-taxa (R. irregularis cluster1) induced by all inoculants was the main determinant of the host benefits. Crop productivity and quality as well as field persistence of inoculated AMF support the use of mixtures of foreign AMF. On the other hand, local mixtures showed a lower impact on native AMF. These results pave the way for extending the study on the effect of AMF mixtures for the production of high-quality forage for the animal diet.

The Potential Applications of Commercial Arbuscular Mycorrhizal Fungal Inoculants and Their Ecological Consequences

“…Thus, using two primers (NS31 and LSUGlom1) to amplify the 3′ end of the SSU and the 5′ end of LSU rRNA, together with the ITS region, Pellegrino et al (2012) [ 67 ] traced an isolate of Funneliformis mosseae from an inoculum, using the polymerase chain reaction–terminal restriction fragment length polymorphism (PCR-(T)-RFPL) method. Pellegrino et al [ 45 ] also targeted the SSU, ITS, and LSU regions to resolve both local and exotic F. mosseae and R. irregularis AMF strains.…”

“…Selecting multiple AMF families having contrasting traits that favor diverse conditions can mitigate these compromises and help improve the chances of success in the field. A mixture of foreign inoculants consisting of F. mosseae and R. irregularis had greater persistence in alfalfa root than the respective single strain and local mixture, while also exerting the greatest impact on plant yield, nitrogen and phosphorus content, and fatty acids [ 45 ]. Merely increasing AMF diversity may not produce additional benefits [ 26 ]; however, the selected AMF should include distant family, which is likely to increase the possibility of finding complementary traits, as shown by Parhar et al [ 115 ], who reported that consortia consisting of distant AMF families conferred greater additive effects than closely related ones.…”

“…Results from a 2012 study by Pellegrino et al [ 48 ] suggest that persistent AMF could sustain yields two years after inoculation. A recent study by Pellegrino et al [ 45 ] also indicated that AMF could sustain positive effects on the host crop several months after inoculation, whereby both F. mossaeae BEG12 and AZ225C enhanced alfalfa yield, nutrients, and fatty acid content. Similar findings were reported by Thioye et al [ 47 ] where the growth-promoting effects of R. irregularis IR27 on Ziziphus mauritiana Lam continued 18 months after planting.…”

“…For example, out of the two non-native Funneliformis mosseae isolates—AZ2256C and IMA1, which originated from the USA and the UK, respectively—only the former was detected two years after inoculation, but in lower proportions compared to the native R. irregularis and R. intraradices , despite early establishment success and the stimulatory effects of both strains on the roots of Medicago sativa [ 67 ]. In a recent study, Pellegrino et al [ 45 ] also reported that although the AMF strains F. mossaeae BEG12 and AZ225C were detected in alfalfa roots two years post-treatment, the AZ225C strains had longer persistence.…”

“…The following supporting information can be downloaded at: , Figure S1: Country location of studies investigating ecological fates of AMF inoculants; Figure S2: Search results on effect of AMF inoculants on indigenous AMF in the field indicating: (A) source of inoculum; (B) site-specific effects on composition and structure of indigenous AMF (Yes means observed effect; No means no effect). References [ 41 , 45 , 46 , 47 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ] are cited in the supplementary materials.…”