Temperature Dependency of Soil Microbial Respiration with Changes in Organic Matter Quality and Clay Type.

The estimated amount of C stored globally in soils is more than twice that present in terrestrial vegetation or in the atmosphere. The IPCC in 2007 predicted that elevated temperatures might induce changes in soil microbial respiration rates and alter the C flux into the atmosphere. Soil organic matter (SOM) is complex, and it is unknown how global warming will affect SOM decomposition. To control confounding factors, we developed an artificial soil that allowed us to examine single factors, such as OM quality or clay type, by controlling other factors, like soil texture, OM composition, pH, and water content. We asked these questions: 1) Will chemical quality of organic matter affect the temperature dependency of soil C mineralization? 2) Will clay type affect the temperature dependency of soil C mineralization? In a chemical quality experiment, artificial soils were amended with organic materials of different chemical properties, inoculated with diverse soil microbes, and incubated at 4 to 34oC. High-quality C (cellulose) responded to temperature quite dramatically, whereas low-quality C (lignin) decomposed very slowly at all temperatures, which indicted that microbial growth was slow and fewer microbes might be able to decompose low-quality C. Furthermore, high- and intermediate- quality C had higher temperature sensitivities than low-quality C on 30-day incubation. In a clay-type experiment, artificial soils had the same amount of clay and the same organic matter, but different contents of kaolinite and montmorillonite. A higher content of montmorillonite reduced CO2 efflux, especially at high-temperatures. This might be because montmorillonite has a larger surface area than does kaolinite, and at high temperature (34oC), montmorillonite may have greater interaction with organic matter than it does at lower temperature.