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

Abstract

Arbuscular mycorrhizal fungal (AMF) inoculants are sustainable biological materials that can provide several benefits to plants, especially in disturbed agroecosystems and in the context of phytomanagement interventions. However, it is difficult to predict the effectiveness of AMF inoculants and their impacts on indigenous AMF communities under field conditions. In this review, we examined the literature on the possible outcomes following the introduction of AMF-based inoculants in the field, including their establishment in soil and plant roots, persistence, and effects on the indigenous AMF community. Most studies indicate that introduced AMF can persist in the target field from a few months to several years but with declining abundance (60%) or complete exclusion (30%). Further analysis shows that AMF inoculation exerts both positive and negative impacts on native AMF species, including suppression (33%), stimulation (38%), exclusion (19%), and neutral impacts (10% of examined cases). The factors influencing the ecological fates of AMF inoculants, such as the inherent properties of the inoculum, dosage and frequency of inoculation, and soil physical and biological factors, are further discussed. While it is important to monitor the success and downstream impacts of commercial inoculants in the field, the sampling method and the molecular tools employed to resolve and quantify AMF taxa need to be improved and standardized to eliminate bias towards certain AMF strains and reduce discrepancies among studies. Lastly, inoculant producers must focus on selecting strains with a higher chance of success in the field, and having little or negligible downstream impacts.

Keywords: arbuscular mycorrhizal fungi; commercial inoculants; community structure; ecosystem functions; metabarcoding; symbiosis.

Figure 3

Overview of ecological impacts of AMF inoculants and driving factors.

Figure 1

(A) AMF genera whose ecological effects were investigated in the field (B) Time-dependent changes in the abundance of introduced AMF according to results from six sites where the abundance of introduced AMF was monitored using metabarcoding twice or more. Introduced AMF: decreased in abundance compared to previous sampling; excluded (not detected in the sample) or abundance remained the same.

Figure 2

Impacts of inoculated strains on indigenous AMF under field condition. The figure was produced by case-by-case analysis of inoculants impacts as reported in the studies listed in Table 2.