Mycorrhizas in the Central European flora: relationships with plant life history traits and ecology

Stefan Hempel et al., 2013. Ecology 94(6): 1389-1399. DOI:10.1890/12-1700.1. Mycorrhizas in the Central European flora: relationships with plant life history traits and ecology

I'm reliably informed there are some mycorrhizae in this photo...

I’m reliably informed there are some mycorrhizae in this photo…


Will Pearse

Aaron David

One of the overarching goals in ecology is to understand the distributions of species and how interacting species shape these distributions. In the world of plant-symbiont interactions, one ongoing question is when is it advantageous to have a symbiont? Hempel et al. compile a dataset of Central European plants and their mycorrhizal associations in order to address several ecological hypotheses. Hempel et al. classify plants as obligate (OM), facultative (FM), or non-mycorrhizal (NM), and ask whether certain types of plants are more associated with various life-history traits (ie. life-form, life-span, pollination, etc.) or environments. The authors find support that different mycorrhizal statuses are over/underrepresented in with different traits and environments. The paper provides strong evidence that mycorrhizal associations may influence plant distributions, and that the benefit of such associations is very much environment dependent. Those such patterns have been shown for individual plant species, Hempel et al. show the generality of this pattern using a large set of plant species.

The authors tackle the exciting question of when it is advantageous to form mycorrhizal associations. For instance, they report that OM plants are found in higher than expected abundance with low soil acidity, while FM plants are found in higher abundance with high soil acidity (NM abundance wasn’t affected by acidity). This result was somewhat puzzling to me, as I would have expected the NM plants to be found with the high soil acidity and the FM to be unaffected. This could suggest that while some plants are able to adjust their associations in different environments, this may not be a general rule for FM plants. The authors define FM plants as those that can form a mycorrhizal association but are not always found with one. Therefore it’s possible that the FM plants as a whole might be composed of NM plants with the occasional mycorrhizal association. It would be interesting to see the FM group split into more definitive categories.

As a fungal ecologist, I found this paper provided interesting insights towards questions of fungal distributions. One of the burgeoning areas in fungal ecology is understanding the distributions of mycorrhizal associations (see the work of Peter Kennedy). Hempel et al.’s results suggest to me that these limitations to mycorrhizae distributions could arise from local environmental conditions or host plant distributions. Of course as the author’s note, it’s not necessarily clear which symbiont is limiting the other. One way to test this idea would be to overlay maps of mycorrhizae distributions with those of plant distributions. Environmental sampling of soil can be used to get a broader picture of mycorrhizae distributions, since many may live as saprobes in addition to being symbionts, though it’s likely the authors could generate a similar distribution map using their available data. Understanding both sides of symbiont distribution would more fully address how species are limited.


Will Pearse

Will Pearse

I’m no mycologist (for what it’s worth I love eating them), but I still thought this was an interesting paper. Literature reviews like this, where massive databases that are going to be of use to future scientists are just thrown out for all to enjoy, are exactly what science should be about. Hurrah.

I think the conclusions of this paper are sound, but I’m going to draw attention to two things just to be picky. Firstly, I have been brought up to think that the phylogenetic corrections employed here should be avoided (listen to Rob Freckleton please). This is a very touchy subject (I’ve heard of people bursting into tears over it!), but in brief the authors create eigenvectors that represent the phylogeny, and then by including them in their analyses hope to correct for phylogeny. A similar approach is used in spatial analyses, but for both it’s hard to know how many eigenvectors is ‘sufficient’, and it’s always unclear to me why you wouldn’t just other methods that directly incorporate the phylogenetic variance-covariance matrix you’re making eigenvectors to describe. Phew. Got that off my chest. Secondly, I wonder what effect the publication bias (that the authors find) will have on these results, particularly as the results are in agreement with what we might expect.

However, as I say, I think the results are pretty sound, and so I wonder whether we could model the co-evolution of plant and fungi. Indeed, there are some very neat new methods (we covered one recently) that examine these questions. More specifically, I wonder if the evolution of a tight association with mycorrhizae would allow a clade to break away from its close relatives and suddenly radiate out into as-yet unexplored habitats and niches. Equally, there could be links between mycorrhizal diversity and plant associations, although I’m almost certain this has already been looked at, and defining fungal species is hard (I think!). I’d quite like to hear from more fungus people!

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About will.pearse
Ecology / evolutionary biologist

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