Microbial role in disintegration and formation of clay mineral-organic matter associations
EMSL Project ID
49562
Abstract
Recent study estimates that soil is one of the three largest reservoirs of organic matter (OM) on Earth. Soil carbon is a highly dynamic carbon repository, and its turnover time has a major impact on carbon cycle and global climate. Virtually all of this soil carbon is intimately associated with minerals via various mechanisms. Association with minerals is known to decelerate OM decomposition because of physical and chemical protection against microbial and enzymatic oxidation, but various mechanisms exist to release OM from such associations, ultimately returning C from soil to the atmosphere as CO2. The mechanisms involved in the latter are not well understood. Past studies have focused on either bulk soil or metal oxides, and the role of phyllosilicates (interchangeably called clay minerals) has not been well studied, despite their ubiquity in soils and sediments, and their high capacity of sequestering OM in both modern soils and ancient sediments. The objective of this research is to establish a quantitative understanding of the role of phyllosilicates in mediating the flow of carbon through the dynamic soil carbon reservoir. The reservoir size and residence time of mineral-associated soil carbon represents a critical element of any attempt to control carbon flow through the biosphere for the purpose of reducing anthropogenic CO2 concentration in the atmosphere. Mineral-OM association also controls the aqueous transport of OM, the bioavailability of OM to microorganisms, and the reactivity of OM towards contaminant migration and nutrient cycling. Therefore, this research contributes to our molecular-level understanding of the fate of soil OM with important implications for environmental challenges and national energy needs.
We hypothesize that microbial activity can not only release and mineralize soil OM via Fe redox process and acidity generation but may also generate new clay-OM associations via generation of microbial products. We further hypothesize that these new clay-OM associations are responsible for the long-term preservation of OM in soils and sediments. We will test these hypotheses by performing laboratory experiments using synthetic soil materials which will be prepared by mixing model clay minerals with 13C labeled proteins and celluloses. These clay-OM associations will be incubated with iron-reducing and acid-producing bacteria in the absence and presence of priming molecules to examine the disintegration of these associations and formation of microbially produced organic materials. The stability of newly formed OM-clay associations will be tested against microbial decomposition. A suite of analytical techniques, including aqueous chemistry, X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, Mossbauer spectroscopy, nuclear magnetic resonance spectroscopy, nano-SIMS, and Fourier transform ion cyclotron resonance mass spectrometry will be used to characterize change of OM as a result of bacterial activity. Respiration rates of the clay-associated OM will be determined and compared across different combinations of minerals and bacteria to reveal the protective role of minerals in OM decomposition. This proposal is a first step towards our contribution to earth system models by incorporating the mineralogy control of OM availability in order to better predict the response of soil carbon stocks to anticipated climate warming. The requested EMSL resources are essential to characterize the interactions among clay minerals, OM, and bacteria to understand the mechanisms and pathways of their interaction.
Project Details
Project type
Exploratory Research
Start Date
2016-10-24
End Date
2017-12-31
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Liu X, H Dong, X Yang, L Kovarik, Y Chen, and Q Zeng. 2018. "Effects of Citrate on Hexavalent Chromium Reduction By Structural 1 Fe(II) in Nontronite." Journal of Hazardous Materials 343:245-254. doi:10.1016/j.jhazmat.2017.09.038
Xia Q., X. Wang, Q. Zeng, D. Guo, Z. Zhu, H. Chen, and H. Dong. 2020. "Mechanisms of Enhanced Antibacterial Activity by Reduced Chitosan-intercalated Nontronite." Environmental Science & Technology 54, no. 8:5207-5217. PNNL-SA-152192. doi:10.1021/acs.est.9b07185
Zeng, Q.-, Wang, X., Liu, X., Huang, L., Hu, J., Chu, R., Tolic, N., and Dong, H. (2020) Mutual interactions between reduced Fe-bearing clay minerals and humic acids under dark, oxygenated condition: hydroxyl radical generation and humic acid transformation. Environmental Science and Technology, 54, 23, 15013-15023
Zuo H., R.K. Kukkadapu, Z. Zhu, S. Ni, L. Huang, Q. Zeng, and C. Liu, et al. 2020. "Role of clay-associated humic substances in catalyzing bioreduction of structural Fe(III) in nontronite by Shewanella putrefaciens CN32." Science of the Total Environment 741. PNNL-SA-153739. doi:10.1016/j.scitotenv.2020.140213