Plant litter decomposition serves as a key control on soil carbon sequestration. Recently, there has been much interest in determining the conditions under which soils gain or lose carbon, especially since soils contain more carbon than the atmosphere and could play a role in global warming. Surprisingly, there remains a paucity of research examining specific interactions between drivers of decay, especially the relationship between microbial community behavior and plant litter chemistry. A more mechanistic understanding of the relationship between these drivers will ultimately help us determine the trajectory of litter decomposition and the conditions in which our soils serve as either a source or sink for atmospheric carbon. In order to examine these relationships, a laboratory incubation was established using Acer saccharum litter and soil from the Oak Openings Region of Ohio (< 1.5% organic matter). Extracellular enzyme activities (ß-glucosidase, N-acetyl glucosaminidase, leucine-amino peptidase, acid phosphatase, phenol oxidase, and peroxidase) were monitored on a consistent basis along with instantaneous rates of carbon dioxide production, microbial biomass (carbon and nitrogen), and nitrogen and phosphorus availability.

Results/Conclusions

Microbial biomass and microbial respiration peaked within the first week of the experiment. This was likely due to the high availability of water soluble substrates early in decay that can be obtained without the production of extracellular enzymes. ß-glucosidase, N-acetyl glucosaminadase, and acid phosphatase activities increased quickly following the first week and peaked within the first month (at approximately 15% mass loss). However, no phenol oxidase or peroxidase activity was measured until the second month of the experiment (> 30% mass loss), likely following the depletion of more labile substrates. Therefore, a distinct functional shift in microbial substrate use was apparent that may be associated with either changes in composition of the microbial community or community shifts in enzyme production.  This mechanistic look at litter decay will provide needed information to help predict the situations in which soils gain or lose carbon.