Submitted to: Biology and Fertility of Soils
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/15/2007
Publication Date: 6/15/2007
Publication URL: handle.nal.usda.gov/10113/54366
Citation: Smith, J.L., Bell, J.M., Bolton, H.J., Bailey, V.L. 2007. The initial rate of C substrate utilization and longer-term soil C storage. Biology and Fertility of Soils. 44:315-320. Interpretive Summary: The world’s atmosphere is increasing in CO2 due to human activities. This CO2 can be used by plants for growth and returned to the soil as litter and other organic substrates. Thus the soil could be a sink for this “human derived” carbon and offset the increase of CO2 in the atmosphere. A better understanding of decomposition processes is needed to develop this strategy. We found that the faster a carbon compound was initially decomposed, the longer it persisted in the soil environment. In addition, we found that the initial amount of the compound that was used and maintained in the decomposer microorganisms was a good predictor of the carbon compound remaining over longer periods of time. It has been long believed that compounds that decomposed rapidly were less likely to persist in soil. With our findings, new avenues of research and management strategies can be developed to enhance C storage in soil systems. An example would be to more finely chop plant residues during harvest of grain crops thereby increasing the decomposability and enhancing the persistence of the residue in the soil over time.
Technical Abstract: Increasing soil C storage is viewed as a legitimate process to offset current increases in atmospheric CO2 from anthropogenic sources. However, microbial transformation and turnover of soil carbon inputs will influence the magnitude of soil C storage. The purpose of this study was to investigate several simple model C compounds to determine their decomposition rates in soil and the relationship between their initial decomposition rate and longer-term C sequestration. Pure 14C compounds of glucose, acetate, arginine, oxalate, phenylalanine and urea were incubated in silt loam soils for 125 days at 24 and 34 degrees C. Total respired 14CO2 and specific activity was quantitatively measured every day for 15 days and residual soil 14C after 125 days. At both temperatures, the percent substrate remaining in the soil after 125 days of incubation was positively and significantly correlated with the percent substrate utilized in the first day. For the two temperatures, the correlation of total 14CO2 and specific activity was significant (R2=.86,.78) as was the percent remaining after 125 days (34 degreesC = 0.75 x 24 degrees C, R2 = .90). The 14C in the microbial biomass ranged from 4-15% after 15 days and declined to day 125 contributing significantly to the 14C evolved during that time. Priming of 12C SOM was negative at day 3 but after was positive and increased to day 12, however the increase in soil C from the substrates at day 125 was greater than the primed C thus soil C increased. The data support the concept that the more rapidly a substrate is initially mineralized the more persistent it will be in the soil. In addition, the percent of 14C initially incorporated into the microbial biomass is also a predictor of the %14C remaining in the soil over a longer period of time.