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For billions of years, plants and their ancestors, the cyanobacteria, have been powerful agents of change on Earth. They pumped out oxygen and squirreled away carbon dioxide, transforming the chemistry of the biosphere. They colonized land and allowed animal life to follow, changing the course of evolution.
Now molecular biologist Wolfgang Busch wants to recast plants into agents of stability, offsetting the tremendous amount of climate-warming carbon dioxide that humans are pouring into the environment. As part of the Harnessing Plants Initiative at the Salk Institute in La Jolla, California, Busch is working on a bold scheme to modify major crop plants so that they grow deeper, bigger root systems, leaving those carbon-rich roots embedded in the soil after harvest time. While we humans get to work cutting back on our carbon emissions, the plants will be busily lending a hand.
A fundamental challenge with this idea is that the shallow roots of crops normally rot and release much of their carbon over the course of the year. The Harnessing Plants team, under the direction of Joanne Chory, has come up with a clever solution. The researchers are modifying plants so that they produce suberin (the primary ingredient in cork) in their roots. Suberin stubbornly resists decomposition, so the roots masses of these "Salk Ideal Plants" could remain in the soil for an extremely long time without sending their carbon back into the air.
Many different parts of the plan have to come together just right for the Harnessing Plants Initiative to work. The plants have to bury carbon efficiently and effectively. The modified crops have to provide all the same seed yield as before. Farmers need to embrace these crops on a global scale. And the rest of the world still needs to keep working on cutting carbon emissions, since plants alone won't save our bacon.
On the other hand, the humongous scale of agriculture provides a unique opportunity for large-scale decarbonization. Busch and his colleagues are therefore plowing full-speed ahead (with some COVID speed bumps along the way) to see whether carbon-sequestering corn and wheat can help us turn down the heat from climate change while also recharging the planet's carbon-depleted soils. An edited version of my conversation with Busch follows.
What drew you to the idea of using plants as a way of burying carbon dioxide in the ground?
I've been conducting research on the genetic and molecular basis of root growth since a long time. I started my own lab almost 10 years ago in Vienna. Then I moved three and a half years ago to the Salk Institute. My main interest has long been the factors in plant genes that determine whether roots grow deep or shallow, and how they respond to the environment.
Just around the time when I was negotiating with the institute, Elizabeth Blackburn [Salk's president at the time] asked the faculty, “What's the most important question that you'd like to address with your fundamental research?” The plant faculty group came up with an answer after considering: Plants are very good at catching carbon, so they thought about how to make this ability useful for addressing climate change. Which they thought, and I thought, was the world’s most pressing problem.
And that fit in with the work you were already doing?
It was a very good coincidence. The main effort at Salk [the Harnessing Plants Initiative] is related to the root system. We're trying to put more carbon in the root system, to make it deeper with more root mass, and to produce molecules such as suberin that keep the carbon longer in the soil. It fits very well my interests. I have been worried about climate
change since I was in middle school. The Harnessing Plants Initiative gives us all the opportunity to merge our research expertise with what we consider the most pressing problem.
Lots of people talk about planting trees, but this is the first I've heard of using crops to fight climate change. Where did the idea come from?
We had an evolving thought process. At first, we thought about using plants to sequester carbon on marginal lands, and we focused on the things that can grow that can grow on those marginal lands. We would do a good thing for the soil there, and for carbon sequestration.
But soon we realized that it's all about acreage. Focusing on [small amounts of] marginal land, we'd have only a small potential to increase its ability to sequester carbon. Plus, every plant species is different in its lifestyle, and if you have to work with the genetics of many different a species, it's a lot of effort.
Then it became obvious that we should be focusing on crops, because there are only a handful of species that populate a vast area. There's more than 600 million hectares worldwide for the four most prevalent crops. There’s also an existing distribution system. You already have people planting and updated seeds every year. You already have a system of incentives that are market-driven, but also government-driven, like crop insurance.
Human activity releases 18 gigatons more carbon dioxide than the Earth can absorb. Enhanced plants could take up some of that excess. (Credit: Salk/HPI)
With all of that acreage to work with, how much could re-engineered crops do to offset human carbon emissions?
We did a back of the envelope calculation. Taking into account published biomass data and the acreage of the planted crops, how much biomass do they yield above ground? Taking into account root to mass fractions, how much of the plant is root and how much is shoot?
We ran these numbers on five target crops that we think we can deal with: corn, soy, wheat, rice, canola. We considered that at some point in the future, 70 percent of the target crops could be enhanced for carbon-sequestration traits. Then we asked, what would happen if we could stabilize 30 percent of the biomass in the root mass?
If you run the numbers, you end up with 5.5 gigatons of CO2 [per year], which is roughly 30 percent of the annual surplus [anthropogenic emissions] that is leaked in the atmosphere. I have to say, this is just a very rough calculation, but it showed us that if we could make plants better, it would have a global impact. Even if only 10 percent of the biomass is stabilized, you have 1.8 gigatons [of CO2 sequestered].
Essentially, it looked like we could offset 10 percent to 30 percent of the surplus of CO2 that is currently emitted in the atmosphere each year. So, that was to us encouraging.
Those are huge numbers, but to get there you’d also have to make a huge change in the crops we grow. What are the steps to make that happen?
That, basically, is the question driving us. We and others have to do much more research to know how much can we actually sequester. There are so many unknowns. We need to know the residence time of carbon [how long it stays buried]. Soil chemistry and local microbiomes will play a role.
We know that the [plant root] traits that we are working on can make a difference, but we want to get to more quantitative models. We’ve started field research — collaborations
with soil scientists, soil biochemists, soil geochemists — to systematically study these questions. Time is short, so we are developing our [engineered plant] traits and coming up with a better quantification at the same time.
This month we are starting two field trials. We wanted to have more, but COVID makes it really hard. Next year we want to have 10 field sites, and then 15, maybe more, depending on whether we can get additional funding. We will be planting our first plants in a couple weeks. One of our field trials will be located in Yuma, Arizona; one will close to the Central Valley in California. Those are with commercial partner field sites. In the long term, we want to work with a couple of universities on this.
Plants absorb CO2 as they grow, then release it as they decompose. Engineered "ideal" plants would store carbon for many decades in deep roots. (Credit: Salk/HPI)
What about the central issue of how long the carbon stays buried? Can cropland hold the carbon in place long enough to be useful?
So, we know from the literature that deeper rooting leads to slow decomposition rates. And suberin or potentially other stable compounds go into long-lived carbon pools, which can have interactions with the soil minerals. These pools are considered to be stable from decades to centuries.
Centuries! I had no idea.
The root depth and the root depth distribution are important factors in how much carbon you can put into the long-lived carbon fractions in the soil, including suberin. We know it will be dependent on soil chemistry. The quantities and the residence time [of the buried carbon] will very much depend on these variables. That’s why we need to get the experiments going, to be able to quantify these things better.
Right, I was also wondering about total quantity of carbon that farmland can absorb. Can you keep burying more carbon there, year after year?
One fundamental consideration is that the soil carbon content has been reduced dramatically over the past century in industrialized, monoculture agriculture. We know there's a huge potential, because if the soil carbon was there before, we can at least replenish it. I can't give you a specific number until we do more modeling. But there is definitely many years of potential carbon sequestration that can happen.
How far along are you in developing and testing the engineered, deep-root plants you would need for agricultural carbon sequestration?
In the first year [of field experiments], we are not planting any genetically changed plants. We are basically taking crops that we know and quantifying different properties of rooting under field conditions. We estimate that our first [suberin-enhanced] test lines will hit the field site next year. The bulk of our studies of the potential of our changes will come in three years, say.
Have you done studies yet to make sure that suberin-enhanced crops are just as good as the ones the farmers are planting now — similar in yield, quality and so
That's a very important and interesting question. What we are currently trying to do is to have a first pass at answering these questions with the help of our collaboration partners. We are looking to see whether there are trade-offs.
A trade-off that one would be worried about would be the root mass to yield allocation [with the increase in root mass coming at the cost of the harvest]. I think there is ample evidence from the literature that it’s not a fixed trade-off. We’re going to try a lot of different strains. We're going to evaluate the genetic recipe to store more carbon in the roots, and at the same time we will also measure the yield.
Despite COVID, we just finished the construction of a 10,000-square-foot greenhouse that will allow us to grow the crops we are interested in — corn, soy, wheat, rice, canola — in field-like conditions. Not true field condition, but field-like.
Wolfgang Busch (right) with his postdoc Takehiko Ogura, examining one of his green test subjects. (Credit: Salk Institute)
Let’s be optimistic and assume the experiments go well. How do you get farmers planting carbon-sequestering crops on the scales needed to have a meaningful impact?
We have started talking to many different agribusiness companies. We are all active scientists in the [Harnessing Plants] initiative. We get invited to talk a lot, we go to a lot of conferences. Most of the companies in this space are very aware of our activities. Some of them have expressed interest in talking more about the specific issues that are important to them.
We know we won’t get the scale we need without partnering with big seed companies and big ag [agribusiness]. Without seed companies that will allow us to distribute seeds to the farmers, and without the farmers who are interested, this project will never fly. We’re also talking to NGOs [non-governmental organizations], because some crops and some parts of the world are not dominated by the big ag companies. We’re trying to spread the word so that NGOs and companies come to us, but we are also talking to as many of them as we can, to see if we can get together.
In the future, there might be market incentives when it comes to things like carbon credits or other ways that governments might reimburse farmers to store carbon in the soil. We’re
exploring all this, because this is more than just a science project. We really want this to succeed.
What about the consumer side? I’m picturing a future in which some customers might seek out products that have a stamp that says “this was made with greenhouse-fighting crops” or something like that.
That would be wonderful if it could be a consumer choice. We are thinking about this, too.
We have this term, the “Salk ideal plant.” It would be wonderful if that would be a label that consumers at some point could say, "Okay, I'm going to make this choice."
How does the Harnessing Planet Initiative fit in with related concepts, like using partially burned plants (biochar) to increase the carbon content of soils? Are these
potentially synergistic approaches?
Absolutely. Just before the COVID lockdown in California, we had a conference called Plant
Carbon Drawdown 2020 at Salk. We wanted to bring together scientists who think about all these different solutions for sequestering carbon, like biochar, enhanced rock weathering, forestry, and enhanced carbon absorption in the oceans and in wetlands.
A lot of these approaches could be important. We just come at the issue from a genetics
perspective because genetics has revolutionized agriculture multiple times. There's a huge potential to make a global impact by changing plants in a manner that's beneficial for humans. But then, everything else, like no-till agriculture [allowing more organic material
to stay in the ground], and supplementing soils with different materials, is also wonderful. The more approaches, the better.
Who is supporting this type of research? Do you get any state or federal funding?
Not yet. We're reaching out to funding agencies to see if that would fit in. The [government] funding is not currently structured in a way that you could say, "Oh, we want to do carbon sequestration using plants." We’re pretty much ahead of the curve. But we're hoping that by providing data and evidence that we can actually do it, we make it possible for the federal government to spend money on this, and to allow other groups to work on this.
We were lucky to get Audacious funding [funded by the TED nonprofit] last year: a large grant to do what we think we have to do, and to show others that there is a potential. Part of where I see us as hopefully having a big impact is to show not only scientists, but also potential funding agencies and the government that there's something else [for agricultural funding] beyond crop yield and stress resilience. That we should, as a society, put money into this because it's really important, and also realistic.
Your idea to remake agricultural crops around the globe is, as you say, rather far ahead of the curve. What are the obstacles you’re most concerned about?
I think the main unknown is, if we change the crop plants, will there be a trade-off? Will there be something that a farmer will not like about it? Until we have the data, we don't know. But we know that we don't need to change the traits radically. Even a small improvement would help. We think that there's not a lot of question that we can make a large impact just by making roots deeper and having more suberin in them. So, we are optimistic about that.
Another unknown is whether governments will be convinced that addressing climate change is something important. Will they take real action on changing the incentives in our systems to make a positive impact?
Personally, I hope there will be an incentive system for storing carbon in the soil, and good protocols for quantifying this. It really depends on governments all around the planet. There are already a lot of incentives given to farmers in the big agricultural regions; it's just a shift in the type of incentives. Countries could say, "We don't really care about providing incentives for drawing down carbon." That's a risk. On the other hand, I'm hopeful, because it seems that governments are more and more willing to think about this.
Clearly you wouldn’t be devoting your energy to a project like this if you weren’t fundamentally hopeful the world will step up and address climate change.
Yeah. We are all really enthusiastic and motivated here! I'm thrilled to be doing this every day.
For more science news and ideas, follow me on Twitter: @coreyspowell
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