Into the Deep: Temperature effects on coupled biogeochemical cycles in deep soil profiles of a wet tropical forest

Ciudadanos Del Karso Inc., San Juan PR

Investigators

Abstract

Tropical forests are an important part of the planet's biosphere. Although they only cover about 15 % of the planet's surface, tropical forests contain two-thirds of live plant biomass and nearly one-third of all soil carbon. Also, these forests exchange more carbon dioxide with the atmosphere than any other terrestrial ecosystem. Changes in carbon cycling in tropical forests, therefore, could substantially alter global atmospheric carbon and, in turn, our planet's future climate. Tropical forests also have very deep soils, yet little is known about carbon cycling of these deeper soils. Temperatures in tropical forests are expected to increase significantly in the next 20 years. Little is known about how tropical forest soil carbon cycling will respond to temperature changes, especially in deeper soils. This research will use a unique soil warming experiment to test hypotheses about how tropical forest soils might respond to future changes. The scientists involved will also use this research to communicate to public audiences the importance of tropical forests for the global environment. The primary goal of this research is to assess relationships between temperature and biogeochemical cycling in deep soils of a wet tropical forest in Puerto Rico. This work takes advantage of the first in situ warming experiment in a tropical forest. Three primary goals of this work are to investigate the mechanisms by which temperature and depth interact in tropical soil to regulate: (1) carbon, nitrogen, and phosphorus cycling; (2) soil oxygen availability; and (3) root lifespan, respiration, and depth distribution. This work will provide information critical to improving our ability to predict tropical forest responses to warming and the potential for these responses to feed back onto future climate. Three 12 m2 circular plots will be warmed + 2 to 4 degrees C relative to three control plots, up to 50 centimeters in depth. Each plot will be instrumented throughout the depth profile for soil temperature, moisture, oxygen, soluble carbon, nutrients, greenhouse gas emissions, and root dynamics. The variation in carbon and nutrient availability along the depth profile will be used to test hypotheses about substrate limitation of microbial and root responses to temperature. The soil and root measurements will further illuminate potential controlling mechanisms on deep soil responses to increased temperature. Ultimately, this deep-warming experiment will significantly advance understanding of processes and organisms below the rooting zone, an exciting biogeochemical frontier. 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.