Amazon Understory Plants Experience Growth Surge Under High CO2 Levels Before Nutrient Constraints Intervene

Tropical forests increase CO2 absorption by redistributing roots to find phosphorus. Discover why nutrient limits may hinder long-term Amazon carbon storage.

By: AXL Media

Published: Apr 29, 2026, 7:51 AM EDT

Source: Information for this report was sourced from EurekAlert!

The Uncertain Future of Earth’s Primary Carbon Sink

The Amazon rainforest is often regarded as a critical atmospheric regulator, yet its ability to adapt to a high-CO2 world remains a subject of intense scientific debate. New research conducted in the Central Amazon suggests that even small understory trees have the potential to buffer climate change by increasing their growth when exposed to elevated carbon levels. However, this increased productivity appears to be a temporary phenomenon that is heavily dependent on the immediate availability of mineral nutrients. According to Lucia Fuchslueger of the University of Vienna, about 60 percent of the Amazon grows on highly weathered soils that are already naturally depleted of essential minerals like phosphorus, creating a potential ceiling for future forest growth.

Experimental Simulation of Future Atmospheric Conditions

To understand how tropical ecosystems will respond to future climates, a team of international researchers utilized pioneering open-top chamber experiments near Manaus, Brazil. These transparent plexiglass structures allowed the scientists to simulate increased atmospheric CO2 concentrations directly within the forest understory while maintaining natural rainfall and temperature patterns. The results showed that after one to two years of exposure, the trees successfully increased their carbon uptake and physical growth. This pilot study, co-led by Nathielly Martins, demonstrates that the initial response of the forest understory is one of rapid adaptation, though the mechanisms used to achieve this growth may not be sustainable over several decades.

Root Redistribution and the Hunt for Phosphorus

The study identified a specific biological mechanism behind the temporary growth boost, involving a strategic shift in how plants manage their root systems. In response to higher CO2 levels, trees were observed redistributing their roots to extract phosphorus more efficiently from the environment. According to the research, roots increased their presence within the litter layer of fallen leaves, releasing enzymes designed to decompose organic matter before it is absorbed into the soil. This highly efficient internal nutrient cycle allows the plants to bypass mineral-poor soil, but it forces them to rely on a finite and rapidly recycling pool of organic resources.