PNNL

Abstract

Increasing soil C storage is viewed as a legitimate mechanism to offset current increases in atmospheric CO2 from anthropogenic sources. However, microbial transformation and turnover of soil carbon inputs will influence the magnitude of net 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 soil for 125 days at 24 and 34oC. 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 14C 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 (C34oC = 0.75 x C24oC, R2 = 0.90). The 14C in the microbial biomass ranged from 4-15% after 15 days and declined through day 125 contributing significantly to the 14C evolved. Priming of 12C SOM was negative at day 3 but became positive, reaching a maximum on day 12, the total increase in soil C from substrates was greater than the primed C. The data support the concept that the more rapidly a substrate is initially mineralized the more persistent it will be in the soil.