Brazilian researchers have unraveled the mystery of a unique soil known as “terra preta da Amazônia,” or Amazon dark earth (ADE), revealing its remarkable potential to turbocharge tree growth rates and promote plant development and forest restoration.
This study, published in the journal Frontiers in Soil Science, introduces a promising avenue for sustainable biotech applications designed to combat land degradation.
The research was conducted as part of FAPESP‘s Biodiversity, Characterization, Conservation, Restoration, and Sustainable Use Program (BIOTA).
The researchers embarked on an in-depth exploration of Amazon dark earth, a soil type known for its nutrient richness and bustling community of microorganisms. Indigenous Amazonians have appreciated these benefits for generations, using the soil in crop cultivation without resorting to artificial fertilizers.
Luís Felipe Guandalin Zagatto is a master’s student at the University of São Paulo’s Center for Nuclear Energy in Agriculture (CENA-USP) and co-author of the study.
“ADE is rich in nutrients and supports communities of microorganisms that help plants grow, among other things. Native people of the Amazon have used ADE to grow food for centuries and don’t need fertilizer for plants,” said Zagatto.
The team discovered that the microorganisms living within ADE, such as bacteria, archaea, fungi, and other microorganisms, provided significant benefits to plant growth.
When they mixed ADE with ordinary soil, they observed a significant surge in the growth of three monitored tree species. In particular, Brazilian cedarwood and Yellow poinciana seedlings grew up to five times their typical height in soil enriched with 20% ADE.
Even more striking, their growth was three to six times greater in 100% ADE soil than in control soil. Ambay pumpwood’s response was most notable. It failed to grow in control soil but thrived in 100% ADE.
In addition to tree growth, the researchers noticed an increase in the dry mass of Brachiaria forage grass, a common pasture plant. This grass flourished in ADE-enriched soil. It grew three times more in soil with 20% ADE, and eight times more in 100% ADE soil compared to control soil.
“The bacteria in ADE convert certain molecules in the soil into substances that can be absorbed by plants. Using a very rudimentary analogy, you could say the bacteria act as miniature ‘chefs’ by transforming substances that can’t be ‘digested’ by plants into substances they can profitably metabolize,” explained study first author Anderson Santos de Freitas.
The nutrient composition of Amazon dark earth was significantly richer than the control soil. It contained 30 times more phosphorus and up to five times more of other nutrients, except for manganese. The soil also demonstrated a higher pH level.
The team collected samples of ADE from the Caldeirão Experimental Field located in the Amazonas state. They used these samples to fill 36 four-liter pots. Then, they divided them into into three categories.
We housed the pots in a greenhouse to simulate future global warming scenarios. In that environment, the average temperature hovered around 34 °C.
Despite the encouraging results, the researchers are cautious about advocating for extensive use of Amazon dark earth. They recognize that it as a finite and protected resource. Their focus is to comprehend the beneficial chemical, biological, and biochemical properties of ADE that foster plant growth, rather than promoting ADE itself.
“We need to understand exactly which microorganisms are responsible for these effects, and how we can use them without requiring ADE as such. We can then try, for example, to replicate these characteristics by means of biotech developments. This study was a first step in that direction,” said Zagatto.
As the specter of deforestation continues to haunt Brazil and the world at large, these findings shine as a beacon of hope. If scientists can harness the insights gleaned from Amazon dark earth to expedite land restoration, we could pave the way for a resurgence of forest growth.
In addition, it would kickstart the resumption of critical ecosystem services. These include climate and air quality regulation, and carbon sequestration in soil.
“We believe these results are promising and show that using the characteristics of ADE in seedling production or even directly in the field can be a way to accelerate tropical forest ecological restoration,” said Zagatto.
Forest restoration involves activities that aim to regain the ecological integrity and functionality of deforested or degraded forest land. This can involve a variety of techniques and goals depending on the particular forest and the extent of the degradation. Here are some key aspects:
This is one of the most traditional and intuitive methods of forest restoration. You can do it manually or use modern techniques such as drone planting. This process requires replanting native tree species in areas that have experienced deforestation.
In some cases, if the conditions are right and there is a nearby source of seeds, forests can regenerate on their own. This can sometimes be the most cost-effective method of forest restoration. This method also guarantees the regrown forest adapts well to the local conditions.
In some forest types, especially those prone to large fires, controlled or ‘prescribed’ burns can be an important tool for forest management and restoration. These can help to prevent larger, more destructive fires. Controlled burns also promote the growth of certain types of trees and plants.
In many areas, invasive species may outcompete native plants and hinder forest regrowth after deforestation. Removing these species can be a key step in restoring these forests.
Forests are not just about trees. The health of the soil and the local water cycle can be critical to the success of forest restoration efforts. This can include techniques like erosion control and the restoration of natural waterways.
Forests are full of wildlife. In some cases, these animals, birds, and insects can play important roles in the health of the forest. Restoring wildlife can involve measures such as the reintroduction of native species, the creation of wildlife corridors, and the protection of critical habitats.
Forest restoration is an effective strategy to mitigate climate change. Growing trees helps absorb CO2 from the atmosphere, thereby reducing the overall amount of greenhouse gases. This is one of the key reasons why forest restoration is increasingly seen as a critical global priority.
Image Credit: Luís Felipe Zagatto/CENA-USP