To the Editor — Soil is the most biodiverse ecosystem on Earth but also the most unknown. More than any other ecosystem, soils have been impacted by humans, but consequences for soil biodiversity continue to be ignored1.
Microbial biofertilizers such as arbuscular mycorrhizal fungi (AMF) have been applied to soil for decades, yet their ability to improve yields is mixed. Some growers view the use of biofertilizers as a viable alternative to fertilizers. However, unlike synthetic fertilizers that are increasingly subject to strict regulation, the impact of biofertilizers on biodiversity and ecosystem function has not been assessed and regulations are lacking2.
Commercially produced AMF inoculants represent a small genetic pool of fungi selected to be at once generalists and aggressive colonizers. These traits have potential to threaten local AMF communities, which may not be resistant to alien introductions.
So, what happens to local soil communities when alien AMF are introduced through commercial inoculants en masse? The role of invasive species in soil ecosystems has received little attention, which is surprising given how much we know about the role of soil biodiversity in ecosystem processes3, and the deleterious effects of invasive species in other systems4. Despite the fact that tools exist to answer this question, it has not been a research priority.
Some believe that for microorganisms, invasion threat is insignificant, since ‘everything is everywhere’. Although preliminary research suggests that many AMF species are cosmopolitan5, there is compelling evidence showing local adaptation of plants, AMF and soil6. It is also not clear whether cosmopolitan taxa represent natural distribution patterns or are the result of human introductions7. What is clear is that AMF diversity is closely aligned with plant diversity and ecosystem services8, thus the soil biodiversity matters.
There have been few attempts to quantify the financial benefits of AMF inoculants9, and even fewer to understand the ecological consequences10. Unfortunately, the lack of baseline data on soil microbial communities means that it may not be possible to determine the relative abundance of all invasive AMF in natural systems. It is possible, however, to identify the abundance of commercial inoculants, as we have the ability to produce genotype-specific markers11. Although there is an urgent need for such research, there is a more urgent need for regulation within the current industry. We cannot wait for science to catch up; international policies on the use of microbial inoculants are needed to protect endemic AMF communities.
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The authors declare no competing financial interests.
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Hart, M., Antunes, P. & Abbott, L. Unknown risks to soil biodiversity from commercial fungal inoculants. Nat Ecol Evol 1, 0115 (2017). https://doi.org/10.1038/s41559-017-0115
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