Exploring economic assessment of the arbuscular mycorrhizal symbiosis

Comparative effects of Serendipita indica and a mix of arbuscular mycorrhizal fungi on the growth, photosynthetic capacity, and proteomics of Schinus terebinthifolius Raddi

MAIN CONCLUSION

Both, Serendipita indica and AMF, show promise as sustainable biofertilizers for reforestation, improving nutrient uptake and stress tolerance, despite contrasting effects on photosynthetic capacity and biomass allocation. Reclaiming degraded areas is essential for biodiversity conservation and enhancing ecosystem services enhancement, especially when using native species. This study investigated Schinus terebinthifolius Raddi, a native Brazilian species, and its compatibility with plant growth-promoting microorganisms (PGPM), including an endophytic fungus (Serendipita indica) and a consortium of arbuscular mycorrhizal fungi (AMF), to identify effective strategies for reforestation in nutrient-poor environments. We observed growth stimulation by both PGPMs; however, S. indica primarily enhanced root weight, whereas AMF improved shoot weight. S. indica's positive effects on root systems could be attributed to increased auxin levels and altered root architecture, which are critical for seedling establishment in reforestation programs. In terms of nutritional status, both treatments increased the content of most nutrients, with higher micronutrient contents in the shoots and higher macronutrient content in roots of inoculated plants. Despite AMF's role in enhancing photosynthesis, plants inoculated with these fungi showed reduced photosynthetic capacity traits, possibly due to lower leaf nitrogen content. The proteomic analysis of Schinus terebinthifolius leaf extracts revealed that, despite the upregulation of several proteins associated with the photosynthetic apparatus in response to S. indica treatment, no enhancement in photosynthetic capacity was observed. We also found several proteins related to oxidative stress in plants inoculated with both fungi, indicating a greater tolerance to adverse environmental conditions. These findings underscore the potential of both, S. indica and AMF, as sustainable alternatives to chemical fertilizers in reforestation efforts, enhancing seedling quality and survival in nutrient-poor soils.

Impacts of Rock Mineral and Traditional Phosphate Fertilizers on Mycorrhizal Communities in Pasture Plants

Intensive fertilizer use can constrain contributions from soil biological processes in pastures, including those associated with arbuscular mycorrhizal (AM) fungi. We evaluated the effect of fertilizers of different P solubility on the colonization of the roots of two common pasture plants by a community of AM fungi in a pasture soil. The treatments were a rock mineral fertilizer, a chemical fertilizer and a microbial inoculant. Subterranean clover and annual ryegrass were grown in pots for 10 weeks. Both fertilizers reduced the proportion and length of roots colonized by naturally occurring AM fungi. However, by 10 weeks, there was a much greater length of mycorrhizal root for annual ryegrass than for subterranean clover. The relative abundance of mycorrhizal fungi in the families Glomeraceae and Acaulosporaceae in roots was not affected by the form of fertilizer, but diversity indices of AM fungi in roots were altered. The chemical fertilizer had a greater negative effect on AM fungal diversity indices in the annual ryegrass roots compared with the subterranean clover roots. The reduction in OTU richness of AM fungi with fertilizer application corresponded with reduced soil pH. Differential effects of P fertilizers on naturally occurring AM fungi in this agricultural soil have the potential to influence the efficacy of P fertilizer use and dominance of plant species in grasslands.

Multitrophic Interactions Between Arbuscular Mycorrhizal Fungi, Foliar Endophytic Fungi and Aphids

Almost all living plants can be simultaneously colonised by arbuscular mycorrhizal fungi in the roots and endophytes in the shoots, while also being attacked by insect herbivores. However, to date, no study has ever examined the multitrophic interactions between these two different fungal groups and insects on any species of forb. Here, we examined the effects of two commercial species mixtures of arbuscular mycorrhizal fungi (AMF) and two foliar endophytes (Colletotrichum acutatum and Cladosporium oxysporum) on the growth of an invasive weed, Impatiens glandulifera, and the aphids that attack it. AMF reduced plant biomass, which was most evident when C. oxysporum was inoculated. Mycorrhizal fungi had few effects on aphids, and these depended on the identity of the endophytes present. Meanwhile, endophytes tended to increase aphid numbers, but this depended on the identity of the AMF inoculum. Throughout, there were differences in the responses of the plant to the two mycorrhizal mixtures, demonstrating clear AMF specificity in this plant. These specific effects were also strongly affected by the endophytes, with a greater number of interactions found between the AMF and endophytes than between the endophytes themselves. In particular, AMF reduced infection levels by the endophytes, while some endophyte inoculations reduced mycorrhizal colonisation. We suggest that both AMF and endophytes could play an important part in future biological control programmes of weeds, but further multitrophic experiments are required to unravel the complexity of interactions between spatially separated parts of the plant microbiome.

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

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.