Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2008
Publication Date: 8/20/2008
Citation: Steinweg, J.M., Plante, A.F., Conant, R.T., Paul, E.A., Tanaka, D.L. 2008. Patterns of Substrate Utilization During Long-Term Incubations at Different Temperatures. Soil Biology and Biochemistry. 40:2272-2728. Interpretive Summary: Global climate change can influence carbon dioxide releases. Understanding how microorganisms are affected by temperature change and substrate quality will determine the influences on crop residue decomposition, carbon cycling, and carbon dioxide release. We wanted to know how temperature influences the efficiency by which the soil microbial community utilizes an added labile substrate and to determine the effect of labile soil carbon depletion on the microbial community’s ability to respond to an added substrate (cellobiose). Data indicate the time required for the microbial community to take up cellobiose increased as the incubation time prior to substrate addition became greater. As temperature increased, carbon utilization efficiency decreased; therefore, the microbial community was more efficient at sequestering carbon at 15° C than at 25° C. Hence, at warmer temperatures due to global warming, microbial communities may release more carbon dioxide per unit of carbon substrate assimilated.
Technical Abstract: Microorganisms play key roles in biogeochemical cycling by facilitating the release of nutrients from organic compounds. In doing so, microbial communities use different organic substrates that yield different amounts of energy for maintenance and growth of the community. Carbon utilization efficiency (CUE) is a measure of the efficiency with which substrate carbon is metabolized versus mineralized by the microbial biomass. In the face of global change, we wanted to know how temperature affected the efficiency by which the soil microbial community utilized an added labile substrate, and to determine the effect of labile soil carbon depletion (through increasing duration of incubation) on the community’s ability to respond to an added substrate. Cellobiose was added to soil samples as a model compound at several times over the course of a long-term incubation experiment to measure the amount of carbon assimilated or lost as CO2 respiration. Results indicated that in all cases, the time required for the microbial community to take up the added substrate increased as incubation time prior to substrate addition increased. However, the CUE was not affected by incubation time. Increased temperature generally decreased CUE, thus the microbial community was more efficient at 15° C than at 25° C. These results indicate that at warmer temperatures microbial communities may release more CO2 per unit of assimilated carbon. Current climate-carbon models have a fixed CUE to predict how much CO2 will be released as soil organic matter is decomposed. Based on our findings, this assumption may be incorrect due to variation of CUE with changing temperature.