Organic matter accumulation and stabilization is an important process that has created large carbon reserves in soils. We know that much of soil organic matter (SOM) occurring below 20 cm has been cycled through soil microbes. However, we have yet to fully understand the implications of this process on SOM stabilization. Soils are extreme environments for microbes. Microbes use biofilms as a protection strategy to survive these environments, as they provide resistance to desiccation, protection from grazers, and other selective advantages. The insitu study of soil biofilms has been difficult, as drying the soil dramatically changes biofilm structure (Donalhkova et al., 2011, Applied & Env. Microbio, 77). Here we employ several scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) techniques that allow us to image SOM and associated mineral interactions. These techniques provide valuable information on SOM-mineral interaction and give insights into the role biofilms play in carbon processing.
Results/Conclusions
Electron microscopy examination of soil samples demonstrates that biofilms and biofilm residues are abundant in soils. The association of SOM with poorly crystalline or short-range-ordered secondary minerals is important for carbon stabilization. This study supports previous work that showed secondary minerals precipitate on and/or in biofilms (Konhauser and Urrutia, 1999, Chem Geo 161; and Tazaki, 2005, Clays & Clay Min. 53) and we infer that this process leads to organic compounds of the biofilm matrix to be co-precipitated within the secondary mineral phases, thereby increasing stability of the OM. We also found abundant soil biofilm (fungal and bacterial) weathering of primary silicate minerals, presumably for nutrient extraction. The inability to “see” biofilms in soils has prevented the understanding of the ecological significance of biofilms in soil development, the techniques used here show biofilms build soil structure by cementing soil minerals and that the microbial processing of organic matter into biofilms is an important process in creating SOM stability.