Ancient Amazonian soil boosted tropical tree growth by 88% on degraded land, study finds

A field study conducted in Brazil’s Amazonas state demonstrated that small amounts of Amazonian dark earth, or terra preta, significantly accelerated early growth of native tree species on degraded land. These findings underscore the importance of soil microorganisms in tropical forest restoration.

Researchers observed that pink trumpet tree seedlings treated with Amazonian dark earth grew up to 55% taller and developed stems up to 88% thicker within 180 days compared to untreated controls. Brazilian firetree seedlings also exhibited increases, growing approximately 20% taller and 15% thicker. The study was conducted on a former cassava field in Itacoatiara, Amazonas, by scientists from the University of São Paulo’s Center for Nuclear Energy in Agriculture, Embrapa Eastern Amazon, and the National Institute for Amazonian Research.

The research, published in BMC Ecology and Evolution, examined the influence of Amazonian dark earth on microbial communities surrounding plant roots, rather than focusing solely on nutrient content. According to lead author Anderson Santos de Freitas, treated plants exhibited substantial shifts in fungal populations, with increases in beneficial microorganisms and declines in potential pathogens. These microbial changes may account for the enhanced growth response, particularly in the pink trumpet tree, which is generally more challenging to establish on degraded land.

Amazonian dark earth is a fertile, anthropogenic soil developed over centuries by pre-Columbian communities through the accumulation of organic matter and controlled burning. As these soils are legally protected, researchers emphasized that the objective is not to extract terra preta for direct application, but to investigate the biological and ecological mechanisms underlying its effectiveness. Tsai Siu Mui, coordinator of the broader project, stated that the long-term goal is to identify microbes and soil processes that could facilitate scalable restoration strategies without dependence on fertilizers or herbicides.

The field trial included two native species with distinct ecological roles: the fast-growing Brazilian firetree and the pink trumpet tree, valued for both timber production and ecological restoration. Seedlings were established without the use of fertilizers, herbicides, or supplemental irrigation beyond natural rainfall. After six months, all plants survived.

Researchers cautioned that these findings represent preliminary results from a single experimental site involving 72 plants and two species. The complete three-year dataset remains under analysis. Nevertheless, the study indicates that restoring microbial relationships in degraded soils may serve as a valuable approach for tropical forest restoration and ecosystem recovery.

Sources: BMC Ecology and Evolution, The Brighter Side of News