Collaborative Research: How iron states impact temperature sensitivity of heterotrophic respiration in humid tropical soils

Humid tropical forests regulate the Earth’s climate, due to their capacity to absorb large amounts of atmospheric carbon dioxide and store it in vegetation and soils. These forests are also the most impacted by changes to the climate, such as global warming. An increase in temperature may cause tropical soils to release more carbon dioxide, further contributing to warming of the atmosphere. This research evaluates how an increase in temperature can affect the release of carbon dioxide from soils, specifically carbon dioxide produced by soil microorganisms through a process called heterotrophic respiration. The research advances our understanding of the fundamental processes that regulate the functioning of soil microorganisms and their production of carbon dioxide, as well as the mechanisms that affect the ability of soils to store and stabilize carbon dioxide. The work has important implications for environmental scientists, engineers, and policy makers working to assess climate change mitigation and adaptation strategies, such as reforestation and afforestation. The project supports the development of new interdisciplinary curricular material at the intersection of microbiology, hydrology, environmental science and engineering, engages middle and high school students around the impacts of climate change to tropical forests, and trains diverse students. Iron is a relatively abundant mineral in humid tropical soils. This work evaluates how the interactions between iron cycles and soil carbon modulate the temperature sensitivity of heterotrophic respiration over time. The research is guided by the hypothesis that short-term soil organic carbon decomposition through iron reduction increases the temperature sensitivity of heterotrophic respiration. In the long-term, it is hypothesized that both microbial community adaptation and physicochemical protection of organic carbon by iron minerals reduce the temperature sensitivity. The project combines experiments and process-based modeling, leveraging the Tropical Responses to Altered Climate Experiment (TRACE), a state-of-the-art field warming experiment in the Luquillo Rainforest in Puerto Rico. Comprehensive experiments with soils sampled from control and warmed plots at TRACE inform their biogeochemical response to temperature gradients and changing iron states. A process-based soil model is applied to analyze observations and mechanistically explain the response to changing temperatures. The project includes training at the undergraduate, graduate student and postdoctoral levels. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.