Warming induces unexpectedly high soil respiration in a wet tropical forest

Background

Tropical forests play a key role in regulating the global carbon cycle, exchanging more carbon dioxide with the atmosphere than any other terrestrial biome.  However, limited in situ experiments constrain understanding of their response to climate warming. Understanding these responses is crucial, as even small changes in soil respiration in tropical regions can substantially influence global carbon dynamics and climate feedbacks.

Goals and Methods

This study examines how tropical soils in the Luquillo Experimental Forest, Puerto Rico, respond to elevated temperatures. The Tropical Responses to Altered Climate Experiment (TRACE) assessed soil respiration responses to +4 °C warming in wet tropical forest soils. Researchers applied infrared heaters to warm three 12 m² forest plots while maintaining three control plots at ambient temperature, each located at distinct topographic positions (upper, mid, and lower slopes). They recorded soil respiration rates every 30 minutes for one year (September 2016–September 2017), generating over 57,000 measurements. Additional field sampling measured root biomass, microbial carbon, and soil moisture to identify mechanisms that drove the observed changes.

Conclusions and Takeaways

This research shows that warming increases soil CO₂ flux by 42–204% across all plots, representing one of the highest responses recorded in terrestrial ecosystems. Although overall respiration rates rise, temperature sensitivity decreases by 71.7%, indicating a shift toward higher baseline microbial activity rather than temperature-driven processes. Microbial biomass carbon increases by approximately 50%, while fine root biomass declines, suggesting that enhanced microbial activity, rather than root respiration, is responsible for the elevated CO₂ emissions. The findings challenge the assumption that tropical soils exhibit low sensitivity to warming and indicate that tropical forests may contribute greater carbon losses under future climate conditions. Continued long-term monitoring is necessary to evaluate the persistence and broader implications of these warming-induced carbon fluxes.