Quanta Magazine

Scientists started to believe that large amounts of atmospheric carbon could be used to bring down the climate change damage.This has been difficult in practice. The idea of increasing carbon stores by planting crops in the ground without tilling has fallen flat. Farmers who drilled the seeds directly into the soil instead of tilling the soil, had their carbon stores grow in the upper soil layers but disappear from the lower ones. Many experts believe that this practice does not increase carbon in the soil, but it can help improve other factors like water quality and soil health.Harnessing Plants Initiative is a form of soil carbon sequestration 2.0. It involves a more direct intervention to basically jam a lot of carbon into the ground.Joanne Chory, a Salk Institute plant geneticist, and Wolfgang Busch, a Salk Institute plant geneticist, had an idea. They wanted to create plants whose roots are rich in carbon-rich molecules. According to their calculations, these plants could sequester as much as 20% of the carbon dioxide added by humans each year if they are grown in large numbers.Researchers focused on suberin, a complex cork-like molecule that is produced by many plant root systems. Suberin and other similar molecules have been shown to resist soil decomposition, according to studies from the 1990s and 2000s.The Harnessing Plants Initiative was noticed with its flashy marketing. In 2019, the Harnessing Plants Initiative raised $35 million in its first round of fundraising. The multibillionaire Jeff Bezos donated $30 million to his Earth Fund last year.As the project gained momentum it was met with doubters. In 2016, one group of researchers noticed that no one had ever observed suberin's decomposition process. The relevant experiment was performed by the authors who found that suberin decomposed quickly.Chory presented the project at a TED conference in 2019. Asmeret Asefaw, a soil scientist from the University of California Merced, spoke at the same conference. She pointed out that suberin, as any other carbon-containing compound should, according to modern soil science. (Berhe was nominated for the U.S. Department of Energys Office of Science. He declined to interview.After hearing Busch speak at an event, Hanna Poffenbarger from the University of Kentucky made the same comment. Poffenbarger recalls telling Busch that she thought it was a mistake to assume that we can breed more resistant roots.Jonathan Sanderman, a Woodwell Climate Research Center soil scientist in Woods Hole (Massachusetts), raised questions about the project earlier this year. He tweeted: I thought the soil biogeochem field had abandoned the notion that there is some magical recalcitrant compound. Do I miss any important literature on suberin?" A second soil scientist replied, "Nope, the literature indicates that suberin will not be broken down like other organic plant components." This is why @salkinstitute based its Harnessing Plant Initiative.Busch acknowledged in an interview that there is no unbreakable biologicalmolecule. However, he cited published papers on suberin's resistance to degradation and said, "We are still very optimistic when we come to suberin."He also mentioned a second initiative Salk researchers are working on in parallel with enhancing suberin. They are working to develop plants with more roots, which could deposit carbon in the soil. Independent experts like Sanderman agree that carbon tends stay longer in deeper soil layers. This puts the solution on possibly firmer conceptual ground.Chory and Busch also have collaborations with Berhe, and Poffenbarger. Poffenbarger will, for instance, study how soil samples containing suberin rich plant roots react to different environmental conditions. Even though these studies will not answer the question of how long suberin stays around, Poffenbarger stated that it is important to know if the goal to keep carbon out the atmosphere for long enough to reduce global warming.Money and momentum are moving toward climate projects that rely on long-term carbon storage and sequestration in soils. In April's speech to Congress, President Biden suggested that farmers be paid to plant cover crops. These crops are not grown for harvest, but to nourish the soil between cash crops. Although evidence suggests that some carbon remains in the soil after cover crop roots are broken down, it is not clear how long.There are not enough bugs in the codeRecalcitrant carbon could also be influencing climate prediction.Scientists began to create complex computer programs in the 1960s to predict the future of the global climate. Climate models attempt to account for soil's interaction with the atmosphere, as soil absorbs and releases carbon dioxide. The global climate is complex and simplifications were required to allow the programs to run on current machines. Scientists made a huge mistake when it came to soil. They completely ignored the microbes present in soil. They instead divided the soil carbon into two pools: short-term and longer-term, according to the humus paradigm.Torn said that recent models, such as those used by the Intergovernmental Panel on Climate Change for their widely read reports are essentially palimpsests, which are built on older ones. They assume that soil carbon exists in both long-term and shorter-term pools. These models could be underestimating the amount of carbon dioxide they will emit and overestimating how much carbon remains in soils.A study published in Nature last summer examined the release of carbon dioxide when soil was artificially heated in Panama to simulate the long-term effects climate change. The researchers found that the soil warmed by artificial heating released 55% more carbon dioxide than unwarmed areas, a significantly higher release than was predicted by climate models. Researchers believe that soil microbes become more active when temperatures rise, which leads to an increase in carbon dioxide.This was particularly disappointing because the majority of the earth's soil carbon is located in the tropics or the northern boreal zones. However, the most popular soil models are calibrated according to soil studies done in temperate countries like the U.S. and Europe. This is a significant change from what was previously possible. Lehmann said that we were doing very poorly in the tropics and high latitudes.Even models of temperate climate need to be improved. Torn and his colleagues reported earlier this summer that deep soil layers in California forests released about a third of their carbon when heated for five years, contrary to what was predicted.Torn stated that models should represent soil closer to its true nature. It is a complex, three-dimensional environment, governed by a diverse community of microbes, bacteria and fungi. Even smaller steps are welcome. She said that adding microbes to a single class of models would be a major step forward.Fertile GroundThe question is: What will replace the humus paradigm?The three-dimensional structure and function of soil is an important factor that has been overlooked for too long. Scientists refer to soil as a separate world, with its own equivalent of continents, oceans, and mountain ranges. This microgeography is complex and determines where bacteria and fungi can travel and what they cannot. It also determines what food they have access to and what they are prohibited from eating.Pett-Ridge said that a soil bacterium is only 10 microns from a large chunk of organic matter, which they would love to destroy, but it's on the opposite side of a cluster minerals. It's almost as if it were on the other side.A second, unexplored, component of a new soil paradigm is carbon's fate within the soil. Research now suggests that most organic material will be digested by microbes. Sanderman said that soil organic matter is a loose mixture of plant matter with varying degrees. The carbon dioxide will be absorbed into the atmosphere. The rest could be consumed by another microbe, another and so forth. It could also bind to clay or become trapped in soil aggregates. A porous clump could contain particles that could be as big as a city but as small as a fortress. Studies on carbon isotopes show that soil can retain a lot of carbon for many centuries, or even longer. Minerals and aggregates may be stabilizing humus if it isn't.There will be many more surprises before soil science can settle on a new theory. A Princeton University group of researchers may have just presented one. They created a simplified artificial soil by using microfluidic devices, which are tiny plastic channels that allow fluids and cells to move around. Researchers discovered that the carbon they added to an aggregate of clay bits was protected against bacteria. The researchers added a digestive enzyme to the aggregate, which allowed the carbon to be released and was quickly absorbed. Howard Stone, an engineer, led the study and said that no one had ever made this connection between enzymes and bacteria or trapped carbon.Lehmann wants to replace the old dichotomy between stable and unstable carbon by a soil continuum model that shows carbon in various stages of degradation. This model, as well as others, is far from complete and, at this stage, it's more conceptually than mathematically predictive.Scientists agree that soil science is undergoing a paradigm shift. It is not known where soil science will end up and what the next edition will look like. Mark Bradford, Yale University soil scientist, stated that we are going through a conceptual revolution. There is no new cathedral. There are many churches that have appeared.