Mycorrhizal status helps explain invasion success of alien plant species

 

pege-mycorrhiza-picture

Menzel et al. 2017 Ecology. Mycorrhizal status helps explain invasion success of alien plant species 98: 92-102.


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John Wilson

For my first ever contribution to the PEGE Journal Club (or anywhere) I chose a nicely written article on the importance of mycorrhizal associations to the success of invasive plants. Menzel et al. analysed interactions between the mycorrhizal status and functional traits of 266 plants species and used the geographic distribution as a measure of invasion success. I think we were all quite impressed that this was possible with publicly available data, and some not-too-magical statistics.

The take home message of the study, going by the title, and first line of the discussion, was that mycorrhizal plants are likely to be more successful as invaders. However, since ~90% of plant families are mycorrhizal, is it so surprizing that most invaders are also mycorrhizal? We were also underwhelmed that facultative mycorrhizals plants (FM) seemed to be present in more grid cells. FM plants are free of the constraints on obligate mycorrhizal plants (OM), and may have alternative strategies to choose from, depending on local conditions. These points at first led us to discuss where the interest lay, particularly for a journal like Ecology. Eventually, pushing some slight publication envy aside, we discussed the interactions with plant functional traits. These seem more interesting than the broad statement that plants make fungal associations. It was interesting that rhizomes are particularly associated with FM plant invaders. I was curious whether they are more important to individual plants with a fungal partner or without, or whether the rhizome was also used a storage organ or not made a difference. It perhaps makes sense that plants with a store of carbon could afford to trade with a mycorrhiza, however, no other storage organs showed a similar relationship. The effect of different lifespans was a surprise for us. Discussing this we decided that we might have expected annuals to spread more widely than they apparently have. Also, that variable lifespans increased OM plant success seemed to be an interesting counterpoint to the variable association with fungi for FM plants, perhaps suggesting that having a “choice” between different strategies is useful for invaders adapting to new habitats.

We then wondered whether there was something particularly unique about habitats available in Germany, since Menzel et al. seemed reluctant to suggest a similar pattern would be found outside Germany. Although the data covered only Germany, it seems reasonable to extend the conclusions to other temperate regions, at a minimum to the rest of temperate Europe. We were curious about these limited expectations, since they also mention results from the UK that agreed with their own. However, contradictory results from California seemed to be enough to cause caution in their interpretation.

To finish up, I am now wondering how these results could be used. Perhaps expanding the models to include different combinations of traits, or taking into account factors like propagule pressure would be useful. Alien plants imported into parks or gardens, can co-exist quite peaceably with their neighbours, maybe for 10 or more years, before eventually overstepping their welcome. I don’t know how feasible this would be, but it would be pretty cool if this sort of information was added to the databases and could help identify or monitor potential invasives before they became invasive.

 

Join us next week where Zarah Pattison will lead the discussion of a paper by Azzuro et al. External morphology explains the success of biological invasions.

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