Using Biomarker Approaches to Predict the Chemical Attributes of Organic Matter That Facilitates Soil Carbon Sequestration.

The chemical composition of soil organic matter (SOM) can partly dictate the degree to which soils can act as a source or sink of atmospheric CO₂. Thus, understanding the pathways of SOM formation is critical to predict the direction and magnitude of the soil carbon-climate feedback. The formation of SOM is largely influenced by the chemical composition of plant litter, the physiology of soil heterotrophs, which controls the breakdown and resynthesis of plant litter, and by the mineral matrix that stabilizes SOM through physiochemical associations. The plant derived decomposition products have greater propensity to be associated with the aggregate fractions whereas the microbial derived products largely associate with soil mineral fractions. The mineral protected SOM has greater stability compared to the physically protected SOM in the aggregate fractions particularly under warmer climates. Here, we discuss the potential of utilizing a biomarker approach to successfully delineate the chemical composition of SOM derived from plant litters of different chemical composition in soils of different mineralogy. Our studies indicated that the input of recalcitrant litter resulted in a higher abundance of plant derived biomarkers in soil aggregate fractions. However, the input of labile litter into an ecosystem accustomed to recalcitrant litter, resulted in the decomposition of plant biomarkers across both aggregate and mineral soil fractions due to microbial co-metabolism. We further discuss the effect of soil mineralogy in regulating the sequestration of plant and microbial biomarkers. Utilizing a biomarker approach, our studies indicated the complex interactions among litter chemistry, soil biota, and minerals in mediating soil C storage in natural ecosystems.