Microbial Contribution to Organic Carbon Sequestration in Mineral Soil.

Soil productivity and sustainability are dependent on soil organic matter (SOM). Our

understanding on how organic inputs to soil from microbial processes become converted

to SOM is still limited. This study aims to understand how microbes affect carbon (C)

sequestration and the formation of recalcitrant SOM (RSOM) in soil. We hypothesize

that biofilm formation on mineral surfaces is an important first step toward the formation

of mineral-organic complexes that eventually form RSOM in soil, a process mediated

by minerals, plant roots, nutrients, and other environmental factors. Specifically, we

are studying the formation of biofilms on typical mineral surfaces to determine how

the lability of biofilm-associated C is affected by properties of mineral surfaces, plant

roots and microbes. We conducted laboratory microbe growth experiments in batch

reactors and replicated columns with or without plant growth. At selected times, we

collected mineral, soil, and biomass samples to conduct a variety of analyses to evaluate

the changes of C pools. The labile fraction of the biomaterials on mineral surfaces

was determined by sequential oxidation with permanganate salt, and total biomaterials

were determined with total organic C analysis. We quantified the microbially-mediated

change of RSOM pools by analysis of microbial biomarker amino sugars in soil. We

determined the biofilm compositions on mineral surfaces using spectroscopic and

microscopic techniques including NMR, FTIR, SEM and TEM. Our results illustrate the

role of the mineral surface in biofilm formation and how formation of RSOM depends

on the interaction between microbes and minerals. This study advances our fundamental

understanding of mechanisms of SOM production and retention in soil.