Recent research shows that drought is forcing tropical trees to reorganize their root systems in unexpected ways: fine roots that once spread near the soil surface are giving way to deeper-growing roots that reach further into the ground in search of moisture. But this adaptive shift is not enough to compensate for the significant loss of roots in the upper soil layers, resulting in an overall decline in root production.
The study, titled “Drying suppresses fine root production to 1 m depths and alters root traits in four distinct tropical forests,” was published in the journal New Phytologist in November 2025. The research was led by Amanda L. Cordeiro under the supervision of Daniela F. Cusack, together with an international team examining how chronic reductions in rainfall affect root dynamics across four lowland tropical forests in Panama. The sites differ in rainfall patterns, soil fertility, and species composition, offering a broad view of how tropical ecosystems respond to sustained drying.
Researchers conducted a long-term rainfall-exclusion experiment, setting up control plots and drought-exposed plots, then monitoring the behavior of “fine roots” down to one meter in depth. Using minirhizotron tubes—transparent cylinders inserted into the ground that allow cameras to observe root growth—they tracked biomass, new root production, root turnover, and shifts in root traits such as arbuscular mycorrhizal (AMF) colonization and specific root length (SRL).
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Belowground Plasticity
The results were striking. In the upper soil layers, between zero and twenty centimeters, chronic drought sharply reduced fine-root biomass, production, and turnover. In response, roots showed increased colonization by AMF fungi, suggesting that trees rely more heavily on fungal partners to obtain water and nutrients during dry periods. However, SRL values remained relatively stable, indicating that root morphology did not change as dramatically as their distribution. In deeper soil layers—below sixty centimeters—fine-root production increased during the dry season and in drought-exposed plots, with one exception: the wettest and most nutrient-poor forest did not show the same shift.
Lead researcher Daniela Cusack noted that while the experimental drought imposed in the study is not as severe as long-term droughts expected under future climate change, the observed responses nonetheless reveal the “belowground plasticity” of tropical forests.
“Trees appear capable of reallocating root growth to deeper soil layers where water remains available, tapping into an emergency supply when surface soils dry out”, Cusack explain.
Co-author Amanda Cordeiro added that these changes in root distribution and traits could have significant implications for soil-carbon storage and long-term ecosystem functioning, potentially altering how tropical forests interact with the global carbon cycle.
“Still, this adaptive behavior has limits. The increase in deep roots cannot fully offset the substantial decline of roots in the upper soil, where most nutrient cycling and water uptake typically occur”, Cordeiro added.
This imbalance may weaken the overall capacity of trees to absorb water and nutrients, reducing ecosystem stability and undermining the ability of tropical forests to act as major carbon sinks. In a warmer world where droughts are projected to become more frequent and long-lasting, the capacity of roots to compensate may be increasingly strained.
Signaling Stress
These findings highlight a looming challenge, as climate change intensifies, the underground networks that sustain tropical forests—roots, microbes, mycorrhizae—are being pushed to their limits. Trees may continue reaching deeper into the soil in search of water, but such adjustments come at a cost. The loss of surface-root production raises concerns about long-term soil health, nutrient cycling, and forest resilience.
In essence, the roots of tropical forests are already signaling stress. While they can dig deeper in search of survival, the broader ecosystem may still struggle to keep pace with accelerating climate pressures. The study underscores the urgent need to understand how these belowground responses will shape the future of some of the planet’s most important and vulnerable forests. (Wage Erlangga)
