Effects of Commercial Arbuscular Mycorrhizal Inoculants on Plant Productivity and Intra-Radical Colonization in Native Grassland: Unintentional De-Coupling of a Symbiosis?

Abstract

There has been a surge in industries built on the production of arbuscular mycorrhizal (AM) fungal-based inoculants in the past few decades. This is not surprising, given the positive effects of AM fungi on plant growth and nutritional status. However, there is growing concern regarding the quality and efficacy of commercial inoculants. To assess the potential benefits and negative consequences of commercial AM fungal inoculants in grasslands, we conducted a controlled growth chamber study assessing the productivity and AM fungal root colonization of nine grassland plant species grown in grassland soil with or without one of six commercial AM fungal products. Our research showed no evidence of benefit; commercial inoculants never increased native plant biomass, although several inoculants decreased the growth of native species and increased the growth of invasive plant species. In addition, two commercial products contained excessive levels of phosphorus or nitrogen and consistently reduced AM fungal root colonization, indicating an unintentional de-coupling of the symbiosis. As there is little knowledge of the ecological consequences of inoculation with commercial AM fungal products, it is critical for restoration practitioners, scientists, and native plant growers to assess the presence of local AM fungal communities before investing in unnecessary, or possibly detrimental, AM fungal products.

The Invasive Plant Impatiens glandulifera Manipulates Microbial Associates of Competing Native Species

“…Commercial inocula very often fail to establish in field conditions, often due to competitive effects with local indigenous species [ 62 ]. Indeed, commercial inocula have been found to benefit invasive species, while reducing growth of native plants from American grasslands [ 63 ]. A detailed analysis of the fate of AM species in the inoculum and the effects on the composition of indigenous communities is clearly needed, yet such analyses are very rarely carried out in mycorrhizal studies [ 64 ].…”

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

“…Despite the growing demand for biofertilizers, results from commercial AMF inoculants have been largely context-dependent, especially under field conditions, contrary to the common laboratory successes [ 29 , 30 , 31 , 32 ]. The inconsistent narrations from the research community regarding the reliability of AMF inoculation as a valid agricultural management technique [ 33 ] are generating low consumer confidence that is hindering large-scale adoption of the technology.…”

“…Unfortunately, most microbial inoculants are selected based on their expressed functional traits in a greenhouse, without proper consideration of the ecologically relevant traits that determine establishment and persistence under natural conditions [ 36 ]. While many cases of inoculation failures could be attributed to poor product quality stemming from the lack of regulatory or quality control frameworks that mandate best practices, resulting in a market flooded by substandard products [ 29 , 32 , 37 ], there is also lack of understanding of ecology and of the mode of action of inoculants [ 38 ]. Duell et al [ 29 ] recently demonstrated that inoculants could decouple native plant symbiosis with indigenous strains in a natural ecosystem already containing a large diversity of AMF community, without conferring additional benefits.…”

“…While many cases of inoculation failures could be attributed to poor product quality stemming from the lack of regulatory or quality control frameworks that mandate best practices, resulting in a market flooded by substandard products [ 29 , 32 , 37 ], there is also lack of understanding of ecology and of the mode of action of inoculants [ 38 ]. Duell et al [ 29 ] recently demonstrated that inoculants could decouple native plant symbiosis with indigenous strains in a natural ecosystem already containing a large diversity of AMF community, without conferring additional benefits. Thus, inoculation in such ecosystems with high mycorrhizal potential may prove unproductive.…”

Impact of Mycorrhizal Fungi from Different Rhizospheric Soils on Fungal Colonization, Growth, and Chlorophyll Contents of Cenchrus ciliaris

“…Symbioses with AMF are especially crucial for the uptake of slow-moving soil nutrients [1]. In nature, DSE and AMF colonize plant roots at the same time, which is frequent in plant ecosystems [14]. Despite the presence of DSE and AMF in plant roots, there has been little research into these symbioses as a whole, and existing information regarding DSE and AMF is uneven [15].…”