Submitted to: Journal of Environmental Monitoring and Restoration
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2008
Publication Date: 12/31/2008
Citation: Hoilett, N.O., Nkongolo, N.V., Kremer, R.J., Eivazi, F., Adisa, S.J., Paro, R.M., Schmidt, K. 2008. Understanding the relationships between microbial biomass, enzymes and greenhouse gas efflux in a secondary forest in Missouri. Journal of Environmental Monitoring and Restoration. 5(1):109-118.
Interpretive Summary: Earth’s atmosphere is dominated by nitrogen (78%) and oxygen (21%) gases with the remaining 1% comprised of a number of trace gases. Trace gases with greatest impact on the environment and human health include carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), which have multiple roles in the atmospheric system. These trace gases can absorb infrared rays that are re-radiated from earth in the lower atmosphere and result in warming the earth’s surface. This is the ‘greenhouse effect’ and these trace gases are often referred to as greenhouse gases. N2O and CH4 can also be transported to the stratosphere and react with ozone to damage the atmospheric protective layer that reduces ultraviolet radiation reaching earth to levels that do not threaten human health. The amounts of greenhouse gases produced and released by soil microorganisms are influenced by land management and agricultural practices such as fertilization, irrigation, and tillage. Little information is available on the interactions of management practices with combined soil biological, chemical, and physical properties on the release of greenhouse gases from soil into the atmosphere. Therefore, our objective was to gather preliminary information on the microbial relationships with greenhouse gas emission from a managed forest in central Missouri. Sampling chambers were installed in the upper soil profile throughout the forest tract to collect and measure the three greenhouse gases released from the soil during 2006 and 2007. Soils samples (20-cm deep), collected near each chamber, were analyzed for moisture, temperature, carbon and nitrogen contents, and microbial activity. When these measured values were mapped according to sample points within the forest tract, higher greenhouse gas emission and soil property levels were found in the upper landscape, reflecting a spatial distribution of gas emission activity within a landscape. We also found relationships between soil thermal properties and greenhouse gas emissions and between soil thermal properties and soil biological activity, which suggested an indirect influence of soil biological activity on greenhouse gas emission. Even though a direct relationship between greenhouse gas production and soil biological activity could not be shown, other soil properties including soil moisture, soil particle composition (texture), and temperature could be interfering with the detection of these interactions. Because this was a preliminary study, subsequent trials where individual properties can be held constant will allow us to better detect direct influence of biological activity. Nevertheless, the results of this study are important to other soil scientists, climatologists, and land managers because they provides a framework for designing studies to better understand how greenhouse gas production is a) influenced by combinations of soil properties, land management and microbial activity; and b) spatially distributed across a landscape. The understanding of gas emission characteristics from soils might be used in eventually controlling accumulation and hazardous effects of these gases.
Technical Abstract: Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) concentrations are increasing at annual rates of 0.5%, 0.75% and 0.75%, respectively. Documented research has established links between soil physical and chemical properties and efflux of greenhouse gases; however a need exists for closer examination of the relationship among soil microbial properties, management practices, and greenhouse gas efflux. This study investigated the relationship between the spatial distribution of greenhouse gases, soil microorganisms and microbial activity within a secondary forest in central Missouri. Laboratory assessments of field samples included determination of gas flux rate, microbial biomass by total organic carbon (TOC) and chloroform fumigation extraction; and enzyme activity by beta-glucosidase assay. Results showed a slight but non-significant decrease in CO2 efflux, and significantly higher efflux of N2O and CH4 in 2007 versus 2006. The higher efflux in N2O and CH4 may be related to similar changes in some soil biological and thermal properties from 2006 to 2007. For example, Beta-glucosidase activity significantly increased from 228.5 µg PNP g-1 soil h-1 in June 2006 to 421.2 µg PNP g-1 soil h-1 in June 2007. Soil microbial biomass carbon (MBC) was correlated with soil thermal conductivity (K) (r = 0.4785; p < 0.05); K also correlated with CO2 efflux (r = -0.4577; p < 0.05). These correlations suggest an indirect influence of soil biological indices on greenhouse gas efflux.