Boosting tree growth in the Amazon rainforest using Amazonian Dark Earths

The restoration of degraded tropical ecosystems, particularly in the Amazon, requires innovative and sustainable solutions. This study investigates the potential of Amazonian Dark Earth (ADE), a highly fertile and resilient soil, as a microbial bio-inoculant to improve the growth of two key tree species, Schizolobium amazonicum and Handroanthus avellanedae. By applying a small volume of ADE, we observed a significant improvement in the growth of both tree species, characterized by enhanced plant height and stem diameter at breast height. These positive results are linked to ADE's ability to fundamentally restructure the soil’s microbial communities. Our findings reveal that ADE acts as a powerful suppressive soil, selectively depleting a wide range of opportunistic and pathogenic bacterial and fungal genera, while simultaneously promoting the establishment of a new, beneficial microbial community. We observed a notable decrease in pathogens, such as the fungus Lasiodiplodia and the bacteria Pseudoxanthomonas, alongside a significant increase in well-known biocontrol agents and plant-growth promoters, including the fungi Metarhizium and Tomentella and the bacteria Rhizobium and Enterobacter. The high nutrient content of the ADE may create a negative feedback loop that reduces the need for certain microbial functions, such as nitrogen fixation, but this targeted microbial “re-wiring” is the key mechanism driving improved plant health. Our work demonstrates that ADEs true value lies in its living microbial community, offering a sustainable and effective strategy for accelerating the restoration of degraded tropical landscapes.