Science

Amazonian dark earth could bring life back to decimated forestland

The research aims to find a way to restore some of the thousands of acres of Amazonian rainforest that have been cut down throughout the last several decades
Depositphotos
The research aims to find a way to restore some of the thousands of acres of Amazonian rainforest that have been cut down throughout the last several decades
Depositphotos

Even though the Amazon is still a powerhouse of plant and animal life, about 18% of it has been cut down since the 1970s. Seeking ways to help get some of that lost forestland back, researchers have turned to a rich soil created by the activities of the Amerindians thousands of years ago.

About 2,000 years ago, as the Amerindian people were living their lives in what is now Amazonia, they inadvertently created an incredibly rich soil. Known as Amazonian dark earth (ADE) or terra preta, this soil was formed as the charcoal from campfires combined with other bits of daily life like animal bones, broken pottery pieces, compost and manure. Not only does the soil contain these ancient components of human life, but it has been found to harbor a rich microbiome as well.

Curious to know if ADE could help restore some of the Amazon's rich rainforests, researchers at São Paulo University in Brazil undertook a simulation. They filled containers with three different types of soil: as a control, they used soil from Amazonian cropland, then they created a mix of the cropland soil with 20% ADE in one container, and placed 100% pure ADE in another.

Next, they sowed grass in each of the containers. Once the grass reached maturity, they cut it down, leaving the roots in place, and planted a variety of trees in the containers. This process simulated what would happen naturally when cropland is left untended and converts first to grassland, and then to forest.

The researchers found that after the trees had grown for 90 days, all soils had fewer nutrients because they had been taken up by the plants, but the ADE soils retained more than the control soil. Both ADE soils also had a greater biodiversity of bacteria and other microbes than the control.

"Microbes transform chemical soil particles into nutrients that can be taken up by plants," said joint lead author Anderson Santos de Freitas. "Our data showed that ADE contains microorganisms that are better at this transformation of soils, thus providing more resources for plant development. For example, ADE soils contained more beneficial taxa of the bacterial families Paenibacillaceae, Planococcaceae, Micromonosporaceae, and Hyphomicroblaceae."

Most impressive is the fact that when grown in this rich microbial soil, the harvested dry mass of the grass was 3.4 times greater in the 20% ADE mixture and a whopping 8.1 times greater in the 100% ADE soil. The trees also fared better. The 20% mixture yielded trees that grew 2.1 and 5.2 times taller by species than in the control soil, and an impressive 6.3 times taller in the 100% ADE soil. One tree species known as Abay pumpwood wouldn't even grow in the control medium, but grew just fine in both ADE soils.

The research team cautions against using actual ADE in reforestation strategies, but says that creating soil rich with the same microbes found in ADE could yield much the same effects, thereby helping to encourage depleted cropland to grow new forests.

"ADE has taken thousands of years to accumulate and would take an equal time to regenerate in nature if used," said senior study author Siu Mui Tsai. "Our recommendations aren’t to utilize ADE itself, but rather to copy its characteristics, particularly its microorganisms, for use in future ecological restoration projects."

The research has been published in the journal, Frontiers in Soil Science.

Source: Frontiers via EurekAlert

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3 comments
TechGazer
The particular microbiome might be what suits soil after 1000 years of not being disturbed. Inoculating fresh soil with those microbes might just cause them to die out quickly. This study result isn't newsworthy until they can cheaply replicate the ADE soil in large quantities. If adding some microbe "could" boost the yield of depleted soil, prove it before calling in the reporters.
Karmudjun
Good article Michael - but many questions unanswered as TechGazer noted. The soil composition or the microbes question doesn't answer how to recreate such conditions! How do you make the fertile ADE in which the useful microbes - if they are identified and can be acquired - can be colonized? There is only one answer in your article to this question of a fertile agar composition: charcoal, bones, detritius of life. We all should know bone meal is useful, charcoal is a great source of carbon, and all the other manure/compost brings a plethora of cellular life support to the soil. I'll start perusing Frontiers in Soil Science to pursue this topic further - the article has very busy reference tables I'll have to "digest" for a while. Thanks for the "heads up" on the topic - but there is so much more information within the journal than you elucidated. But a great start! Instead of a dead end - the article opens up possibilities.
COCO LOCO
This is commonly called biochar and there have been a lot of studies about it. It’s made by burning feedstock in an anaerobic environment, this retaining the carbon, aka char. To reply to TechGazer, it isn’t so much about the inoculation of microbes but the microporosity of the actual char that allows microbes to thrive. Think of the carbon char as a “mini-hotel” that creates micro-structures that these microbes can easily inhabit and facilitate the exchange of nutrients. Dr. Lima out of New Orleans has been studying biochar and animal manures for many years. Check it out! It’s really exciting stuff.

Also, I find it likely to be inaccurate to characterize this as an Amerindian accident. Native people’s the world over have tended land and noticed what works and what doesn’t work for millennia.