Microbially Mediated Plant Functional Traits

My Annual Review is available online, representing a ton of work by my fabulous coauthors (thanks Stef, Eric, Joel, Scott and Esperanza!).

Plants are rife with bacteria and fungi that colonize roots and shoots both externally and internally. By providing novel nutritional and defense pathways and influencing plant biochemical pathways, microbes can fundamentally alter plant phenotypes. Here we review the widespread nature of microbially mediated plant functional traits. We highlight that there is likely fitness conflict between hosts and symbionts and that fitness outcomes can depend on partner genotypes and ecological factors. Microbes may influence ecosystems through their effects on the functional trait values and population dynamics of their plant hosts. These effects may feed back on symbiont evolution by altering transmission rates of symbionts and scale up to ecosystem processes and services. We end by proposing new avenues of research in this emerging field.

DOI: 10.1146/annurev-ecolsys-102710-145039

This arose after a workshop at UC Davis, where Joel Sachs was an invited speaker. Since Joel, Stef and myself all work with rhizobia and legumes, we hang out to talk shop whenever possible (I love talking about science). Joel gave a great talk about his potential cheater strain of Brady that makes lots of tiny nodules that are chock full of bacteria—reminding me of a similar account by Parniske of a strain that has a similar phenotype but only on particular host genotypes. Parniske shows this crazy picture of “naked” rhizobia inside nodules, which does not happen in normal symbioses. Typically, the bacteria remain enveloped in a plant membrane to comprise the symbiosome.

Anyways, Stef and I were taking Joel to the airport and we were talking about how we’d love to actually work on something together. I proposed my rhizobia-legume fitness correlation meta-analysis project—version 1 is now complete and in prep. (Anyone interested in version 2, i.e. compiling hundreds of studies on ABM & NBM? Email me!) Joel said he was getting interested in ‘the rest’ of symbiotic (and non-symbiotic) microbes, so we came up with a simple idea: see what is known about who alters plant traits and explore the evolutionary and ecological implications.

Eric (key member of the Medicago project team) had been reading about mycorrhizae and Scott actually works on plant functional traits and how to scale them up to ecosystem & global processes. Then we contacted Esperanza, who Stef and I met when she was visited Doug Cook’s lab. Esperanza is a leader in the field of bacterial endophytes and she leant her vast and foundational knowledge to the cause.

So we put together our proposal, went through a couple rounds at the AREES editors’ meeting, and got the thumbs up! From there we tried a google doc, a wiki, and finally ended up mainly just sending our sections around in doc files. We spent a lot of time on the structure, then divvied up each section to a person. I collated, then we’d meet and discuss. The sections were supposed to change owners multiple times, but never quite did… at one point someone said their section was like a baby and they weren’t ready to pass it to a stranger (though we’re all friends…).

Then we got close to the deadline and I started orchestrating Skype meetings where people were assigned/volunteered for specific, small tasks like re-working a concept or looking for additional literature on X. Around this point we had a major hang-up on the definition of a “functional trait”. Our starting point had been Cornellison’s table of functional traits, which we used to try to estimate the potential impact of microbes on plant functional traits. I still default to this in my head, since most definitions seem to center largely around measurability on individuals. This is more complicated for things like drought tolerance, since you need multiple copies of the same individual to measure it. Working with selfed genotypes of Medicago, I’m totally down with that.

Then there was the word count reality check. I think the final manuscript is a little under 50% of the original length, due to several weeks and several sleepless nights. I tried to Strunk and White it: “Make definite assertions. Avoid tame, colorless, hesitating, non-committal language.” —Rule 12 William Strunk, Jr.


As our test audience, we were fortunate to have R. Ford Denison (evolution of cooperation in rhizobia master) and Scott Saleska (scaling from biosphere to atmosphere ecosystem processes); they gave us fantastic suggestions. We hope that it stimulates research and discussion!

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