Studying plants across deep time

Boyce, an associate professor of geological and environmental sciences, received undergraduate degrees in biology and literature from Caltech before entering a paleontology graduate program at Harvard University. He joined Stanford's geobiology program from the University of Chicago in July.

Boyce talked to School of Earth Sciences writer Ker Than about what attracted him to his chosen field, and how he feels about being called a "genius".

How did you learn about winning the MacArthur Fellowship?

I was having  lunch with (Stanford paleontologist) Jon Payne when I received the phone call. The last time I tried to have lunch with Jon, I received a call about a sick toddler in daycare. So Jon didn't think anything was amiss when I answered the phone and disappeared for 20 minutes.

The MacArthur Foundation allows grant winners to tell one person about the news. Whom did you tell?

I told my wife. She said she loved me already, and that she would not love me less after I'd won.

How do you feel about being called a "genius"?

I'm not thrilled about it, but what are you going to do? In some ways, it would be more pompous to stop people from saying it, so I just try to ignore it because it will die down pretty quickly.

What's the most unexpected comment, question, compliment or invitation you've received related to winning the MacArthur?

The most fun part about all of this has been hearing from people that I haven't talked to in 15 years or so, such as the dean's secretary from when I was an undergrad at  Caltech. It's been really wonderful in that regard.

The MacArthur Foundation chooses Fellows based on their demonstration of exceptional creativity in their fields. What is the role of creativity in your own research? And do you have a favorite example?

One time, while visiting another lab for a geochemical analysis when I was a postdoc, the machine I had flown out to use broke before I arrived. Situations like that can often be very fruitful because they force you to sit and think about or do something else that you wouldn’t have considered otherwise.

In that case, I happened to find a textbook on industrial wood pulping. Paper engineers think about trees, and I think about trees, so I figured surely something interesting would come out of reading that book.

It turned out the paper people had completely different notions of how different biochemical compounds—the lignin and different polysaccharides like pectin and cellulose—were distributed in the walls of the wood cells compared to what I had read in botanical sources.  I had no doubt that the book was correct because the paper industry had a lot of money invested in that being true.  I figured both camps could be right, and that we were just looking at different plants.

I ended up doing a project with some plant physiologists demonstrating that the distribution of different biochemical compounds varies at a submicron level within these wood cell walls across different evolutionary lineages. That turns out to really matter for the plants.  Wood is how a tree transports water, but it also is the source of structural support. And different patterns of wall layering could maximize transport properties or structural properties, but not both, and different plants had different strategies to handle these tradeoffs.

That discovery came about because a mass spectrometer broke and I ended up reading a book about paper pulping and talking simultaneously to plant physiologists and an organic geochemist. It's always been about that for me—seeing if old questions can be answered by approaching them from an unexpected direction.

What attracted you to paleontology and the study of fossil plants in particular?

I liked biology in high school, and decided to study it in college, too. But the focus available at Caltech was molecular biology, and while the program there was very good, it was both intensive and very reductive in a way that just didn't interest me.

I liked the evolution stuff more. I took a couple of geology classes and I liked those. I liked the deep time and I liked the scale. So when it came time for graduate school, I applied to paleontology programs. I did that even though I had no prior experience in paleontology. I don't know if I could have gotten away with that now.

In graduate school at Harvard I had to make a decision about which to study, plants or animals. Most people study animals, but I had no particular preference. While sitting around drinking coffee one day, I had an epiphany that plants have cell walls.

Because plants have cell walls, you actually get anatomical preservation, which you don't get with animal cells. That is, you get original remnants of those original cell walls. Also, because plants have cell walls, they don't move around during development the way animal cells do. That means you can look at a leaf's mature form and see how it got there in a much more direct way.

Your research helps explain how angiosperms, or flowering plants, became the dominant plant group on Earth. What did you find?

There was a detail that I had known about since I was a graduate student.  It was that flowering plants have more leaf veins than any other plant group, by a factor of like four or five.  I'd never seen that mentioned anywhere because the fern people look at ferns and the angiosperm people look at angiosperms and very few people look more broadly across different groups.

But as a paleontologist, I had spent a lot of time looking at leaf fossils. So I knew that flowering plants didn't just have more veins than any other living plant group, but that they had more veins than anything else that ever lived throughout all of Earth's history.

Scientists have primarily focused on the reproductive characteristics of angiosperms to explain their dominance. Flowers allowed angiosperms to attract very specific animals to pollinate their flowers and to spread their seeds. Their floral biology helps explain why there are so many angiosperm species, but it doesn't explain why they also make up most of the plant biomass on the planet.

I think the answer to that comes down to these physiological characteristics like vein density. More leaf veins means flowering plants can transpire more water, and they can take in more carbon dioxide for photosynthesis. That makes them grow faster.

Another way to think about it is that the reproductive characteristics of flowering plants allowed them to subdivide the landscape very finely, but it's their physiology that gave them most of the landscape.

What scientific questions drive your research?

What I really like is noticing the questions that don’t get asked because we naturally project a modern understanding back onto the fossil record.

For example, if you look at an illustration of a carboniferous forest 300 million years ago, at first you'd feel totally okay with it. There are trees, and bugs buzzing around, and vertebrates. It's a forest.

But when you start thinking about the details, it's totally wrong. None of the vertebrates are herbivores, and the trees had bizarre anatomies and architectures unlike anything alive today. So how did those ancient forests work?

How have plants impacted the Earth?

Plants represent most of the planet's biomass and they strongly influence global chemical cycling, climate, atmospheric composition, sedimentary processes, etc. So, in a real sense, the evolution of plants is the evolution of the Earth's surface.

How do you plan to spend the MacArthur grant money?

I don't really know, and I kind of like not having a plan. There are questions that I can imagine asking differently now that I have the funding to ask them. Such as, what if I wanted to count every leaf on a tree?

I'm actually kind of serious about that, because it touches upon questions of the maximum range of rates over which a growing branch can produce new leaves. Determining those kinds of architectural constraints could explain a lot about the ecological limits on plants of the distant past, but those are difficult questions to answer without support.