Mediate global warming by engineering lignin in crop plants

[Simon Quellen Field]

Here's an idea I have not yet explored quantitatively, but I thought I'd pass along for comments.

In the Carboniferous era, plants had evolved lignin, but microbes had not yet evolved to degrade it. It took a hundred million years or so for that to happen. In that time, carbon got locked up in plant material which eventually got buried and formed our current coal supplies. As carbon got sequestered, and trees evolved, carbon dioxide levels fell, and oxygen levels rose.

If we could engineer the lignin in our crops so that it was not degradable, we could lock up a lot of carbon as a by-product of our current activities.

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[David Murphy]

imagine if all the leaves from trees were about as biodegradable as bits of plastic bag. 

it would probably mess up a lot of other things along the way. Imagine the buildup of non-biodegradable dead vegetable matter clogging up rivers, suffocating soil and simply clumping on the ground blocking out the light from the plants bellow like some kind of permanent snow. 

Don't forget the increased problems with fires from all the piles of dead plant matter.

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[Simon Quellen Field]

If we engineered a bacterium to sequester carbon, it would not be able to compete with wild strains that did not waste that metabolic energy doing unproductive things.

Screwing around with ocean ecology has a host of unknowns that bother smart people.

But with food crops, we are already creating our own ecologies on land that was previously hosting organisms we were not as fond of. In other words, factory farming is already making so many changes to the local ecology that we don't think twice about destroying whole ecologies and replacing them wholesale. We call it crop rotation.

Weathering of mountains is how calcium gets back into the ocean to soak up the carbon dioxide.

We could speed that up, at some cost in energy. If we get that energy from fossil fuels, it may not make sense. If we get the energy from renewable sources that could have replaced fossil fuel use, it is just as bad. Artificial weathering either has to be very low energy, or we have to wait until we no longer put carbon into the air to get energy.

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On Tue, Jun 3, 2014 at 12:39 PM, Chuck McManis <chuck....@gmail.com> wrote:

It is an interesting thesis but would it be any more difficult to simply design a strain of E.coli that sequestered carbon? The whole 'seed the ocean with iron so that plankton will take up more carbon' is a pretty solid example of that which was widely opposed, is that something you would favor Simon? A couple of E.coli projects have been around for converting CO2 into long chain hydrocarbons as a bio diesel precursor.

And the other question which I think about from time to time is the carbolic acid cycle. So the ocean is busy taking in CO2 which is resulting in acidification of seawater, so can we use chemistry on a very large scale to precipitate that carbon out as calcium carbonate or something? I don't have any idea on that side of things.

[Simon Quellen Field]

There isn't a lot of lignin in leaves.

Lignin is the tough stuff that holds the plant up.

The non-degradable plants would be the wheat and rice crops mostly (or exclusively -- we decide as a matter of policy).

What is left after harvest can be plowed back into the soil. The non-lignin parts would degrade, leaving the lignin skeleton to hold moisture and nutrients, improving the soil. Currently, one of the best soil improvers is biochar, used to make terra preta. A non-degradable lignin would have similar properties.

Quite a bit of the soil is already made of non-biodegradable materials like quartz, feldspar, mica, and other minerals. If your bits of plastic bag were shredded finely enough (into sand grains) they would indeed be a decent way to sequester carbon in the soil. Unfortunately, they weren't made from carbon in the air, so it is not a solution to the climate crisis. But lignin is made from carbon in the air.

If we had policies that made it cost effective for farmers to char the crop remains and return it to the soil, then bioengineering would not be part of any solutions. But I thought it would be an interesting topic for this group to think about. Are there genes out there in the wild that already produce carbon containing molecules that do not biodegrade? The beauty of lignin is that it is already needed by the plant, so no extra metabolic cost is wasted by the plant, and crop productivity should not suffer.

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[Patrik D'haeseleer]

Actually, we usually want to go the other way: make agricultural waste *less* recalcitrant, so we can turn it into biofuel. Otherwise, your scheme would still require you to spend some money and energy to bury ag waste underground, and then you'd have to spend more money and energy pulling fossil fuel out of the ground. If you can turn ag waste into biofuel, you kill two birds with one stone.

Rice straw and husks are actually a significant problem right now. It degrades very slowly because of the high silica content. So rice growing regions wind up with these mountains of rice straw in the fields that take ages to degrade. Yes, I guess you could dump it into a landfill somewhere, but unless you can get some sort of carbon offsets for that, it's probably not economically feasible.

[Eugen Leitl]

On Wed, Jun 04, 2014 at 12:54:30AM -0700, Patrik D'haeseleer wrote:

> Rice straw and husks are actually a significant problem right now. It
> degrades very slowly because of the high silica content. So rice growing
> regions wind up with these mountains of rice straw in the fields that take
> ages to degrade. Yes, I guess you could dump it into a landfill somewhere,

Should be gasified, and ash/biochar spread in the fields it comes from
to close the material loop.

[Simon Quellen Field]

I agree that using biomass to offset fossil fuel use is the first thing to do.

The prevents the fossil carbon from going into the air.

But it does nothing to remove the carbon already in the air.

Once we have weaned our energy production off of fossils, sequestering carbon from the air would be the next step. Doing that in our own anthropogenic ecologies, instead of playing with natural ecologies, still has some advantages.

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[John Griessen]

On 06/04/2014 06:33 AM, Eugen Leitl wrote:
> It
>>degrades very slowly because of the high silica content. So rice growing
>>regions wind up with these mountains of rice straw in the fields that take
>>ages to degrade.

It's going to become building material reinforcement one of these days when robot plasterers
can handle troweling and packing it into meta-concrete forms and onto stucco walls.