Redox And Reactive Minerals: The Impact Of Redox Fluctuations On Iron-Organic Matter Associations And Soil Carbon Cycling
EMSL Project ID
48832
Abstract
Tropical forest soils store more carbon (C) --in the form of plant litter and decomposed organic matter-- than any other terrestrial ecosystem and play a critical role in the production of greenhouse gases (methane, nitrous oxide, carbon dioxide) that affect both atmospheric chemistry and climate. Humid tropical forests also exchange vast amounts of carbon, water, and energy with the atmosphere and can lose large amounts of dissolved carbon via runoff and leaching. The rapid carbon cycling characteristic of wet tropical ecosystems is driven in part by high rainfall and warm temperatures. This combination of environmental conditions causes tropical soils to alternate between oxygenated and anaerobic conditions, affecting the behavior of both tropical soil microorganisms and short range order Fe minerals that regulate many aspects of the belowground carbon cycle. In the coming half-century, tropical forests are predicted to see a 2 - 5 degrees C temperature increase and substantial differences in the amount and timing of rainfall. Although the importance of tropical soils to the global C cycle is clear, we have a surprisingly poor understanding of how the carbon cycle of wet tropical soils will respond to these climate changes. This makes predicting future climate impacts extremely difficult. Our ability to forecast how new moisture and temperature patterns will shape tropical microbial activity is also a gap in knowledge because so little is known about the fundamental abilities and chemical preferences of tropical soil microorganisms. As wet tropical forests experience shifts in rainfall patterns/abundance, redox-based microbially-mediated processes that produce greenhouse gases, or generate precursors of stabilized soil carbon, will likely be affected. In the later case, shifts in rainfall patterns will also alter the abundance and composition of redox-sensitive iron minerals that serve to sorb and 'store' organic carbon under aerated conditions and act a potent electron acceptor for organic carbon under anoxic conditions.
In this project we will examine the functional potential (via proteomics) of tropical soil microorganisms as they experience shifts in soil moisture and oxygen availability. We will also track the degradation and fate of organic carbon compounds (13C-NMR, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR MS)) that are mobilized in soils undergoing redox oscillation, and will evaluate the role of Fe mineral phases (Mossbauer) associated with organic carbon. In addition, we will collect supporting data in our home labs: 1) NanoSIMS, to map 13C/15N organic matter associations with Fe-oxides at high spatial resolution (REF 1) ; 2) microbial community composition and biomass via amplicon sequencing (16S and ITS Itags) and qPCR of bacterial and fungal populations; 3) microbial gene expression (metatranscriptomes) and stable isotope tracing (REF 2-4); 4) 14C age dating of bulk field soils, DOC and soil density fractions; and 5) 13CO2 production using CRDS (Picarro) and dynamics of added 57Fe spikes using ICP-MS (REF 5). Our results will feed directly into numerical models we are developing to describe carbon accumulation/degradation in redox dynamic soils. Our refinement of the mechanisms governing carbon dynamics during fluctuating redox conditions will also inform broader numerical models seeking to forecast the future tropical soil carbon balance.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2015-10-01
End Date
2017-03-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)