A few of my favorite things…

By Kelly Ramirez

The influence of global changes (climate change, nitrogen deposition, urbanization, etc) on microbial communities is really one of my favorite research topics and sustains my job as a science policy – microbial ecologist (that is a thing, right?). Last month Drs. Jennifer Lau and Jay Lennon published in PNAS, on a few of my favorite things– “Rapid responses of soil microorganisms improve plant fitness in novel environments.” Soil, microbes, plants, global change, complex interactions- what more could you ask for?

(As an added bonus, I have sketched out some highlights, which may, or may not, help elucidate the content)

In this manuscript the authors set out to address the complex interactions of species (in this case plants and soil microbes) under drought conditions and how those interactions may be important for adapting to climate change. The influences of climate change on our ecosystems is wide ranging, and as ecologists we are especially concerned with how climate change will affect the communities we study, whether that is microbes, plants or animals, and in turn how those community changes will feedback to ecosystem effects. As the authors state- climate change effects can be catastrophic to communities and ecosystems (e.g. coral reefs (Baker et al. 2004)).

The questions and directions to explore within the realm of climate change research are seemingly exhaustive…and often equally disheartening. One such area that is of specific concern is the loss of biodiversity caused by climate change. As an environment changes (i.e. warmer, dryer, colder, greater oscillations in temperature) the organisms living there must adapt to the changed (novel) environmental conditions or die (or at least maybe have lower fitness).

Sketch 1: Under historic conditions the mouse and plant are living next to each other. Under climate change conditions, the mouse escapes up the mountain to more optimal conditions, but the plant stays…

Sketch 2: For the plant: if it stays in the now drier conditions, in some instances it may die. In other instances, it may live. What are the mechanisms behind the plant living and triving?

In this manuscript the authors focus specifically on adaptations to climate change through rapid evolution (reviewed here) – where species evolve to the novel environment over fewer generations and shorter time scales. This mechanism is especially important for organisms that are stationary (i.e. plants) and cannot easily move to a location with the preferred climate conditions. However, climate change is a rapid process and it is unclear if organisms can evolve quickly enough to keep up with the changing conditions. Further, making it even more difficult to predict the effects of climate change on interacting species and communities.

So a quick summary of the questions addressed:

HOW do species adapt to climate change? (i.e. if an area receives less rainfall with climate change resulting in drought conditions, what are the mechanisms species use to adapt?)

IF communities can adapt to these climatic changes through rapid evolution, will changes occur fast enough?

 

FINALLY, no species is an island, therefore how do changes in one species/community influence or interact with changes in species sharing the same environment.

Sketch 3: Here is an artful illustration of plants and microbes interacting in the soil. Here is a nice article about those interactions.

To address these questions, the authors used a greenhouse experiment, growing plants for 3 generations under either wet or dry conditions. After establishing a ‘dry’ plant community and a ‘wet’ plant community they transplanted ‘dry’ plants to a ‘wet’ soil*, and ‘wet’ plants to ‘dry’ soil*. *The soil and corresponding microbial community had also been maintained for 3 plant generations under either wet or dry conditions- meaning there were dry- and wet-adapted microbes

Then they asked- do ‘dry’ plants do better under dry conditions and do ‘wet’ plants do better under ‘wet’ conditions? And how do soil microbes (dry or wet) affect these dynamics.

What did they find?

First, plant type ‘dry’ or ‘wet’ grew equally under drought conditions. This tells us that the 3 generations was not enough time for the plants to ‘rapidly’ evolve.

However, plants did not grow equally when soil microbe type matched the growing conditions. In other words the best combination was:  ‘dry’ soil microbes + drought conditions = better plant fitness and ‘wet’ soil microbes + wet conditions = better plant fitness. This tells us that the soil microbial community did rapidly adapt during the 3 generations of the plants. Well almost… to test if the soil microbial community did rapidly adapt to drought conditions the authors examined the soil microbial community composition. And they found that ‘wet’ soil microbes were different from ‘dry soil microbes:

Sketch 4: Under drought conditions, after 3 plant generations, the microbial community shifted, from one of O, X and Y to one of A, B and C.

 

But here are the real results:

Fig. 2 from the manuscript: Briefly, fungal communities (top) from ‘dry’ soils (dotted circles) are different from those of ‘wet’ soils (solid circles). This trend held true for bacterial communities as well (bottom).

In summary, while 3 plant generations was not sufficient for plants to adapt to drought conditions, it was sufficient time for the soil microbial community to respond and that response in turn had a positive effect on plant fitness when subjected to drought conditions.**

I enjoyed this manuscript for a number of reasons:

1. Topic: Climate change is affecting ecosystems drastically and if we are to help manage and mitigate the chaos in any way we must first understand the complex interactions between species and communities.
2. Novel experimental study to address a pertinent question: As microbial ecologists we frequently ask who is there and what are they doing, but it is much more rare to link who is there and what they are doing back to larger processes and interactions, and then relate that back again to how will all of this matter with climate change. Rapidly we are establishing a much clearer of picture of soil microbial communities function and composition, the next steps are to clearly relate this knowledge back to global change questions, and identify areas where it matters for management and policy.
3. I love that you can still get a PNAS publication with T-RFLP microbial data in the age of high throughput sequencing madness. That is all.

(This is a simplified summary of the manuscript and results, my goal with this post was to present results for those not as familiar with microbial ecology or global change or artful sketches of plant-microbe interactions)

References:

1. Jennifer A Lau, Jay T Lennon (2012) Rapid responses of soil microorganisms improve plant fitness in novel environments. Proceedings of the National Academy of Sciences of the United States of America 109 (35) p. 14058-62

2. Baker et al. (2004) Coarl reefs: Corals’ adaptive response to climate change. Nature 430:741-741

3. John Carey. Is global Warming Happening Faster Than Expected? Scientific American

4. Ary A Hoffmann, Carla M Sgrò (2011) Climate change and evolutionary adaptation. Nature 470 (7335) p. 479-85

5. David A Wardle, Richard D Bardgett, John N Klironomos, Heikki Setälä, Wim H van der Putten, Diana H Wall (2004) Ecological linkages between aboveground and belowground biota. Science (New York, N.Y.) 304 (5677) p. 1629-33

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