Soil has a microbiome, too
The Netherlands is home to windmills. It is home to clogs. It is also home to intensively farmed cropland. Holland is small in size. But is has a large population. This means that the country has historically needed savvy agriculturalists to feed its people. It grows less and less of its own food. So the government has to buy out farmers to return cropland to a wilder state.
This program started several decades ago. That's according to Martijn Bezemer. He is a biologist. He works at the Netherlands Institute of Ecology. Back then, conservationists would simply stop planting. They would let the land be. Or, they would strip off the top layer of soil. They would leave the sandy subsoil exposed to the elements. Neither approach met with much success. They waited for a healthy grassland to take hold. But the soil was degraded after decades of high-intensity farming. It wasn’t recovering.
The government recruited Bezemer to try and speed up the restoration process. His group began experimenting with the process of inoculating degraded soils with dirt from healthy ecosystems. Bezemer’s group wanted to use healthy microbes to treat a sick ecosystem. This is the way physicians can treat many intestinal problems. They transplant gut microbes from a healthy person into a sick one.
Their initial work in greenhouses and on small plots impressed Machiel Bosch. He is a nature manager. He works for the government. He was helping to oversee the restoration process in the Netherlands. Several years ago Bosch received a new parcel of land. He invited Bezemer to try his soil microbial transplants on a larger scale.
The results were published in the journal Nature Plants. They revealed that small soil inoculations from grassland or heathland could help determine which plants would colonize the area and thrive in the future. “You don’t get the right plants if you don’t have the right soil,” says Bezemer.
Scoop up a handful of soil. The dirt you hold in your palms forms the basis of the life around you. This ranges from the earthworms crawling in your garden to the raptors hundreds of feet in the air. But soil is not just a lifeless pile of earth. Symbiotic fungi lives in plant roots. They are known as mycorrhiza. They help the plants extract vital nutrients. Other microbes break down decaying plants and animals. They replenish the materials used by the plants.
Scientists believed that soil microbes were broadly similar around the world. But more recent work has revealed that microbial populations are actually hyper-local. That's according to Vanessa Bailey. She is a microbiologist. She works at Pacific Northwest National Labs. She studies at the foot of Rattlesnake Mountain. It is in Washington State. That soil is actually quite different from the soil at the top. From the foot to the top there is an elevation change. It is just 3500 feet.
What does this mean for scientists? It is two-fold. It means that microbial diversity in soil alone is probably far more immense than anyone had thought.
“We have the tools now to describe microbes in much greater detail than even five or ten years ago.” That's according to Noah Fierer. He is a microbiologist. He works at the University of Colorado at Boulder.
“Yet 80 percent of the soil microbes in Central Park are still undescribed. There’s a lot of diversity to reckon with.”
The second implication is that two different ecosystems could have very different microbes living in their soil. A plant might survive drought. But not because of something inherent to its physiology. Instead it may be because of the assortment of symbiotic microbes in the dirt.
Plant the seeds elsewhere. They may not be able to germinate. They may not grow. And they may not thrive. This is without the proper mixture of bacteria and fungi. Researchers are learning more about the depth and complexity of these interactions. And Bezemer has realized that could explain why his native country’s attempts at returning farmland to native ecosystems was failing.
The process could work, Bezemer believed. But it could work if the right soil was present. He tried moving the soil wholesale. It wasn’t a problem for small projects. These were in pots and greenhouses. But scaling any projects up would be difficult. That's because soil is heavy. And it is hard to move. These early trials gave Bezemer enough data to show that seeds did better when they were planted in soil taken from other ecosystems where those species thrived.
This way, the plants grew better. And the transplanted soil also prevented weeds and other non-desired plants from dominating the new system. This was before the native species had a chance to take hold.
For Bezemer, the problem with this approach was the amount of soil needed. Conservationists would effectively have to strip all of the soil from healthy ecosystems. This would be necessary to adequately convert farmland to grass or heathland across the Netherlands. But if microbes were the important factor, then maybe he didn’t need massive quantities of dirt.
The experiment took six years. But the data clearly showed that the donor soil steered the former agricultural land towards an ecosystem that looked like the original source. Grassland soil created grassland. And heathland became heathland. Stripping the topsoil allowed for stronger donor soil effects. And the ecosystems also recovered faster.
Bailey published her own study. It was on how climate change might affect soil microbes. She says that these results show the effects of donor soil on ecosystem restoration. They also show how competition between soil microbes can affect how plants grow. The likely reason was that the inoculations had less of an effect when the topsoil wasn’t removed. It was competition between the existing microbes and the ones in the transplanted soil.
Soil remains an ecological black box for scientists. Researchers are just beginning to understand how microbes that we can’t even see could potentially shape the world around us.