Do mycorrhizal fungi alleviate the impact of different factors of global change on soil processes?
We mostly care about the effects of mycorrhiza on plants; but what about effects on soil?
In a recent post I reported on a recent study from our lab, where Bo Tang/ Jing Man and Anika Lehmann showed in a meta-analysis that arbuscular mycorrhizal (AM) fungi help soils better deal with the impacts of drought. These fungi don’t make the effects of drought disappear, that’s impossible; but the effects of drought on soil processes were milder in the presence than in the absence of these fungi. What was surprising about this analysis: there are not so many studies that measure the soil impacts of AM fungi. There are far more studies that are concerned with plant effects.
So this made me think: is this a general effect of the symbiosis? In other words, do AM fungi help soils deal also with the negative impacts of other factors of global change?
Let’s have a look at some possible mechanisms.
The first one is, in fact, effects on plants, where is a lot more data. By helping plants cope with certain environmental stress factors (e.g. salinity, drought), the symbiosis allows positive effects of plants on soil processes to continue more than would be possible without the symbionts. Plants can then continue to input carbon into soils, via rhizodeposition, leaf and root litter, fueling microbial processes in the rhizosphere and perhaps beyond what would otherwise be possible without AM fungi having helped plants deal with stress.
The soil aggregation function of AM fungi is often cited in the context of carbon storage in soils; which is certainly true. But soil aggregates can also encapsulate pollutants, inorganic pollutants like heavy metals, or microplastics or perhaps synthetic organic pollutants, and hence render them less available. This in turn prevents their toxic effects from more fully unfolding in the soil, leading to continued soil functioning at a rate perhaps higher than would be expected without AM fungi.
There are likely other functions of AM fungi that can become important for soils, related to the production of an extensive extraradical mycelium in soil that is important for carbon processing and microbial interactions.
Maybe there are also mechanisms that reside at higher levels of the ecological hierarchy, in particular I am thinking about the plant community level. Plant communities with AM fungi can have higher diversity (depending on effects of the symbiosis on the competitively dominant species), and more diverse plant communities may be able to buffer effects of global change on soil better.
What about the positively-acting factors of global change (i.e. where effects of the factor are nominally positive, which doesn’t mean the same as ‘desirable’)? For example, elevated atmospheric carbon dioxide concentrations often lead to more carbon input into soils. Can AM fungi help soils profit more from these effects? A recent meta-analysis from our group seems to suggest that at least in terms of plant growth effects this may be true: benefits of such ‘positively acting’ global change factors were higher with than without AM fungi. Is this also true for soil effects?
I believe this is a very interesting angle of mycorrhizal ecology research. It seems much of the work has been focused on plant performance effects (for obvious reasons), but maybe we should think more about these soil effects. From an ecosystem perspective, they may be just as important…
What do you think? Please let me know in the comments.
Really interesting ideas! I have been loving all the fungi/mycorrhiza discussion lately. This one made me think about the interactive effects AM fungi might have on the ecosystem services of other organisms. Such as burrowing invertebrates are known to aerate the soil or promote nutrient cycling, so how would the presence of AM fungi affect this? Or vice versa? Anyways, thanks for your newsletters! I always like reading them.
Thank you for sharing these insightful thoughts. We recently set up a similar experiment in the field, and I'm also considering the mechanisms by which AM fungi mitigate the ecological effects of multipule global change factors. I have two additional thoughts. First, soil is a heterogeneous environment, and the impact of global change factors on soil processes should exhibit a broad range of heterogeneity. The hyphae of AM fungi may demonstrate a stronger adaptation capacity to cliamte change induced heterogeneity at a small scale compared to plant roots, helping plants adapt to global climate change. For example, they may grow more hyphae in N-rich patches (Hodge et al., 2001). Additionally, one possible function is that mycorrhizal fungi might promote the synergy between plants and beneficial soil microorganisms through hyphosphere processes (Duan et al., Cross-kingdom nutrient exchange in the plant - AM fungus - bacterium continuum, Nature Review Microbiology), thereby enhancing the overall resistance of the plant-soil system.