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This week in science: biodegradable plastic, crops on Mars and deer vs. caribou


It's time now for our regular science news roundup with our friends at NPR's SHORT WAVE podcast, Emily Kwong and Regina Barber. Hi, y'all.



BARBER: Good to see you.

SUMMERS: Good to see you in person, both of you.


SUMMERS: OK, so how this works is you have brought us three science stories that caught your attention this week. Tell us what they are.

BARBER: How to grow plants on Mars.

KWONG: And how white-tailed deer are expanding throughout Canada.

BARBER: And how to build a plastic that can break itself down.

SUMMERS: I mean, we've got to start with the self-degrading plastic. I mean, that really just sounds too good to be true.

KWONG: Right? OK. Just fair warning - this is just a pilot study. It was published in the journal Nature Communications this week. But it is exciting because plastics are a global problem, Juana, right? Like, according to the EPA, less than 10% of U.S. plastic waste has been recycled.


KWONG: Plastics also take decades to decompose. Like, they never truly go away. They just break down into smaller and smaller pieces.

SUMMERS: And if I remember correctly, these are called microplastics.

BARBER: Right. So what if I told you that there are these researchers that found a way to embed something special in the plastic to help break it down more quickly? Guess what it is.

SUMMERS: I really should have paid more attention in science class. You got to tell me.

KWONG: We'll help you out. It's microbes that love to eat this kind of plastic called polyurethanes that are found in all kinds of things - watch bands, phone cases and footwear.


BARBER: And to break down this polyurethane, the researchers identified a strain of bacteria which they then engineered to withstand extreme high temperatures so that the bacteria could survive the manufacturing process.

KWONG: And the final product, this microbes-plus-plastic construction - it looked kind of like linguini pasta when it came out.


KWONG: It was this, like, long, yellowish strip. And the researchers then put it directly into compost, causing the microbes to wake up and do their thing.

SUMMERS: To eat the plastic.

KWONG: Yes. And after only five months, more than 90% of the plastic had degraded.


KWONG: Adam Feist, a researcher on the study, was pretty pleased with that result.

ADAM FEIST: As our consumption of plastic, you know, skyrockets and is expected to continue to do so, we really need to think about, you know, effective lifecycles of these polymers, you know, what the time of use is and then what the time of, you know, breakdown is.

SUMMERS: That's really interesting. So here's a question. Am I going to be seeing microplastic in my shoes anytime soon?

KWONG: Not anytime soon. Plastics experts I spoke to had a lot of follow-up questions for these researchers. They wanted to know things like, would a product like this break down in a landfill as easily as it did in a lab? Or is this microplastic better than, say, plant-based alternatives already on the market? Still, it is promising. The team wants to do more tests, applying this methodology to other kinds of plastic to ultimately tackle the global plastic pollution problem.

SUMMERS: Worthy goal, for sure. But speaking of innovation, Gina, I understand you've got a story about growing crops in space.

BARBER: Yes, I do. And growing food and space is, like, really crucial to future space exploration because bringing cargo from Earth is way too expensive. So scientists like Rebeca Goncalves are looking at growing tomatoes, peas and carrots in Mars-like soil called Mars regolith right here on Earth.

REBECA GONCALVES: We don't need to wait until there's an actual colony on Mars to start researching with actual Mars regolith. Like, we can get there within, like, 90% of the way done already.

SUMMERS: OK, hold up a second. Earth does not have Martian soil, at least that I'm aware of. So how exactly did they grow these plants?

BARBER: Yeah. So scientists know from Mars rovers what Mars soil is like, and they mixed up a simulation of that using materials from Hawaiian volcanoes and the Mojave Desert.

KWONG: And like the Martian soil, this regolith soil doesn't have a lot of nutrients that plants need. It doesn't have any water. It doesn't have any organic material for them to feed on.

SUMMERS: It sounds like some pretty sad soils.

BARBER: Mars is harsh, Juana.

SUMMERS: So. OK, so tell us. What did they do with the soil?

BARBER: Well, we already know that we can grow stuff in this regolith. And they experimented with this technique called intercropping, which is an ideal growing method when resources are limited. The ancient Maya used it to grow the three sisters - corn, beans, and squash. And think about this intercropping stack as, like, the corn providing a structure for the beans. On the bottom, there was squash, where leaves would provide shade to the roots to, like, help maintain soil moisture.

SUMMERS: OK, so using this intercropping technique for the study, what did they find?

BARBER: Yeah. So in this Martian-like soil, intercropping did help. It helped the tomatoes grow better when they were grown with peas and carrots - pretty cool. Unfortunately, though, the peas and carrots didn't do as well. The study was published in PLOS One this week.

SUMMERS: Hopeful for me. I like tomatoes better anyway.

BARBER: Tomato salads on Mars.


BARBER: Here we go - love it.

SUMMERS: So, I mean, this technique seems to help with some crops. But aren't there a whole lot of other variables to consider when you're growing stuff in space, say, like - I don't know - lower gravity?

BARBER: Well, Rebecca isn't worried about lower gravity specifically because, like, tomatoes are already grown in microgravity in the International Space Station. But Amy Grondin, another microbiologist not on the study, mentioned that there are other growth and safety factors that need to be looked at, like metals and other toxins in the Mars soil. Still, she thinks the study is a really promising start.

SUMMERS: Interesting. All right. Let's move on to our last story. I've heard that deer are moving north. Tell me what that's about.

BARBER: Yeah. So wildlife ecologists have seen whitetail deer expanding their range in North America over many decades. And since the early 2000s, they've moved north into the boreal forests of western Canada. And these forests are, like, full of spruce and pine trees, sandy soil and, like, freezing winters with a lot of snow. So living there is really harsh.

SUMMERS: I don't know about y'all, but that does not exactly sound like a place I want to live. So why...


SUMMERS: ...Are these deer moving there?

BARBER: It's kind of like a mystery because - is it the warmer climate in these forests that's happening recently, or is it human development that might be pushing them up? So Melanie Dickie, a wildlife biologist at the University of British Columbia Okanagan - she tried to disentangle these two things by hiding 300 cameras in western Canada. And she collected data for five years. And then her team used these images to estimate the number of white-tailed deer there.

KWONG: Now, the beauty of this setup, Juana, is that the team place these cameras along two axes. Some were north to south, where the winters got more intense as you move north. Some of the cameras were east to west, where the further you move west, the more human disturbance there is. So they were able to look at both factors.

SUMMERS: And what did they find?

KWONG: Well, they found that, like, a warming climate seemed to play the most significant role in the movement of deer, although human land use was a smaller factor. And they published all these results last week in the journal Global Change Biology.

SUMMERS: OK. And I don't want to be a hater here, but why does it matter if the deer are moving into these new areas?

BARBER: No, fair question. OK. Melanie described these deer as an invasive species. With the deer come more predators like wolves. And while the deer are able to cope with the wolves, other species, like the boreal caribou, are not. So Melanie says these caribous - they have evolved to mostly just avoid areas with a lot of predators. They're not equipped to handle these wolves at all.

KWONG: And she also says that the deer is just, like, one piece of the puzzle for caribou. But having like, more information about what exactly is driving the deer expansion will help her and other researchers find out, like, where to start when it comes to restoring land and protecting wildlife like caribou.

SUMMERS: That's Emily Kwong and Regina Barber from NPR's science podcast SHORT WAVE, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Thanks.

KWONG: Thank you.

BARBER: Thank you so much.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Emily Kwong (she/her) is the reporter for NPR's daily science podcast, Short Wave. The podcast explores new discoveries, everyday mysteries and the science behind the headlines — all in about 10 minutes, Monday through Friday.
Regina G. Barber
Regina G. Barber is Short Wave's Scientist in Residence. She contributes original reporting on STEM and guest hosts the show.