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Plant Roots: When Biology Is More Than Biology

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Lately, I keep having the same conversation over and over:

Curious: "So, what do you do?"

Me: "Oh, I'm a Ph.D. student in physics."

Curious: "Wow, that sounds hard. Do you do quantum mechanics?"

Me: "No, I study plant roots."

Curious: "Wait, what? What are you studying that for? Aren't plants biology?"

Me: "Yeah, about that... Funny story."

To say it in a sentence, I work with an interdisciplinary team of scientists at Cornell University growing plants, making 3-D movies of their roots develop, and interpreting what we see with mathematical theories based on well-established physical principles.

Okay, it's a mouth full, but if that doesn't grab you, let me just say watching 100 hours of plant growth in under 10 seconds in 3-D is pretty awesome. Don't take my word for it, have a look for yourself:

What does it mean? Well, if you never saw the movies, and instead just looked at the roots after a couple days, you might think, "Oh, of course they're wiggly. All roots are wiggly because they're alive and that's what living things do. So there's nothing really special here, right?" The experiments tell us that this reasoning is dead wrong. In fact, measurements from 3-D movies of roots grown under controlled conditions demonstrate that some of the more interesting shapes roots make come from universal physical principles that apply to all things, living or dead. It's true that roots do things you wouldn't expect a steel rod to do -- for example, roots grow. But the "living" aspects of the problem can be neatly compartmentalized and treated on equal footing in the context of Newton's laws. Ultimately, this lets us predict what the roots will look like well before they fully develop.

Describing the growth of roots in the language of physics represents a fundamental shift in perspective. By no means is our group the first to make this leap; we're part of a growing branch in the biophysics community. That said, I'd like to point out that with new perspectives and technology come new discoveries that are just beginning to open the door to useful applications.

Here's a problem that matters to anyone who likes to eat food. Whether you believe in climate change or not, the current drought ravaging parts of the U.S. is changing soil conditions, making it tougher to grow food, and increasing prices at the grocery store. Taken with an increasing global population, a big problem is getting bigger -- farmers are being squeezed on both sides by supply and demand, leading to food prices that are unaffordable for the poorest among us.

As climate and agricultural practices change soil conditions, the question becomes: How will food crops fare in their new environment? In some areas, plants are now growing in a loose topsoil atop a stiff, compact subsurface foundation. This is a real-life example of the controlled conditions we studied in our experiments. What do the experiments tell us? If the topsoil is too soft, then the roots won't be able to brace against it as they try to penetrate into the subsurface soil -- a problem since that's where they'll find the water needed to survive. Though a variety of factors lead to compacted subsurface soil, the punch line is the same: Soil can be overtilled -- a counterintuitive result since tilling is such a cornerstone of modern agricultural practices!

In the interest of full disclosure, I have to add that the roots in the 3-D movies weren't grown in real soil; far from it, in fact. In order to be able to see them grow, we used a transparent block of gel much like Jell-O. It turns out however, this didn't affect our results as much as you might think. We did some checking with chopped blocks of gel, which more closely resemble the grainy nature of soil, and ultimately found that our conclusions weren't significantly changed. Nevertheless, it's still not the same as live in-the-field experiments, a place where, for the time being, our results are waiting to be applied.


For more information, visit here.

To read the paper, visit here.

This work was funded by the National Science Foundation and the U.S. Department of Energy.