Redox And Reactive Minerals: The Impact Of Redox Fluctuations On Mineral-Organic Matter Associations And Microbial Carbon Transformations In Tropical Forest Soils
EMSL Project ID
49804
Abstract
In tropical ecosystems, changes in future Earth Systems will likely affect both the amplitude and periodicity of redox oscillations due to predicted increases in temperature and changes in the frequency of precipitation. Our research will measure how shifts in soil oxygen/redox patterns affect the fate of carbon in soil. Redox conditions are a major driver of soil trace gas fluxes, microbial community dynamics and carbon stabilization in tropical soils, but are poorly constrained by soil biogeochemical process models and underestimated in representations of upland soils. In wet tropical soils, low redox events are common, occurring on daily to weekly timescales and driven by high biological oxygen demand, high moisture (limiting O2 diffusion), warm temperatures and abundant labile carbon. These oscillations prime tropical soils for rapid C, Fe and P cycling, and regulate mechanisms of both carbon stabilization (mineral sorption) and loss (dissolved organic matter (DOM) leaching). Although the importance of tropical soils in the global C cycle is clear, we have a poor understanding of how soil C cycling in these systems will respond to change; this makes predicting future Earth System impacts extremely difficult. Better forecasting of soil C cycling in wet tropical soils depends on a mechanistic understanding of organic matter-mineral interactions, and more detailed knowledge of the chemical nature of DOM.Our prior research has shown that microbial community composition responds to shifting O2 availability, correlated with significant differences in DOC concentration and molecular composition (measured by FTICR-MS). These results, along with parallel studies of biogeochemical responses (pH, Fe speciation, P availability), suggest our wet tropical soils are a highly responsive microbial and geochemical system, where the frequency of low-redox events controls exchanges of C between mineral-sorbed and aqueous pools. In our soils, Fe-organic matter complexes also appear highly vulnerable to variable redox effects, and can rapidly solubilize and re-precipitate in response to local Eh conditions. However the role of Fe reducing events in liberating DOM in tropical soils remains poorly understood.
In our proposed EMSL research, we will use isotope tracing and molecular characterization of both mineral-sorbed and dissolved soil C following manipulations of soil redox. The composition of DOC during oxidation and reduction events will be monitored by FTICR-MS. DOC pools will be characterized with high mass accuracy using high field FTICR-MS and NMR. We will identify 57Fe mineral phases using Mossbauer analysis and attempt to target 57Fe-OM linkages with 21T FTICR-MS. We hypothesize that shifts in soil O2 availability and Fe (hydr)oxide mineral crystallinity will have a significant effect on microbial C processing, leading to altered degradation of complex C compounds and mineral stabilization. Microbial activity will be measured using shotgun proteomics and protein-stable isotope probing ('Pro-SIP'). Our results will directly benefit attempts to reduce uncertainties in model predictions of tropical soil carbon balance.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2017-10-01
End Date
2021-03-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Bhattacharyya A., A. Campbell, M.M. Tfaily, Y. Lin, R.K. Kukkadapu, W. Silver, and P.S. Nico, et al. 2018. "Redox fluctuations control the coupled cycling of iron and carbon in tropical forest soils." Environmental Science & Technology 52, no. 24:14129-14139. PNNL-SA-135734. doi:10.1021/acs.est.8b03408