Global climate change will increase the frequency and duration of drought in many places. These droughts not only affect plants, but also the microbes in the soil that are critical for plant growth. In a study published this week in Proceedings of the Royal Society B, CSUN biologist Casey terHorst and colleagues documented that drought indeed has large effects on the diversity and composition of bacteria and fungi in the soil. However, the evolutionary history of the plants, whether they evolved in a wet or dry environment, had an equally big effect on the composition of these soil microbes. “Drought is really tough on plants, and only the tough plants survive. When they do, they make baby plants that are also pretty tough and aren’t affected by drought as much”, says terHorst. In just a few generations, plant populations can evolve to be drought-tolerant. The study finds that the evolutionary history of the plants had just as big of an effect on the microbes as does the drought itself. “We were really surprised at how important evolution was in just this really short time period…just three generations of plants. For these types of plants, that’s only about six months!”
When microbes were growing in wet soil, they were reasonably happy and weren’t affected very much by the type of plant growing next to them. But in dry soil, microbes were stressed out, and only those ones who get along with the plant are able to survive.” The study suggests that we need to consider this sort of rapid evolution much more when thinking about how organisms will respond to climate change. “In this experiment, if we hadn’t accounted for the evolutionary history of the plants, we would have completely misinterpreted the effect of drought on the microbes”, says terHorst. Interactions between plants and microbes are crucial for both ecosystem health and for feeding a growing population. Predicting how the evolution of one affects the other will help us better understand how ecological and agricultural communities will respond to the increasing threat of drought.
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Above: Evolutionary experiments were conducted in these mesocosms. In the foreground mesocosm, conditions were dry and only a few hearty plants survived to reproduce. In the background mesocosm, plants were well-watered and many more plants survive and reproduce. The composition of the plant community has a big effect on which bacteria and fungi survive in the soil.
