Print PageDecomposition of a range of soil organic matter (SOM) labilities requires a suite of vastly diverse microbial functional groups found in soil. It is intuitive that a shift in the soil microbial community function has the potential to alter carbon cycling rates at global scales. However, decomposition models (CENTURY, ROTH-C) don’t account for changes in microbial community function as a mediator of SOM decomposition. This omission could be a source of inaccuracy in decomposition models, particularly if global change affects microbial functioning. We hypothesized that as the labile substrates were depleted, the soil microbial community would both decrease biomass and experience a shift in its SOM decomposition kinetics. We were specifically interested in how a long-term incubation (707 days, hereafter pre-incubated soils) without substrate addition impacted microbial decomposition of SOM. We used a 42-day laboratory incubation to compare the microbial community response to a labile substrate addition in pre-incubated versus newly-sampled soils.
Results/Conclusions
The pre-incubated soils had very low biomass, but biomass grew in response to added substrate and respiration of the added substrate approached levels found in the fresh soils during the course of incubation. The respiration rates in the pre-incubated soils were generally lower than those of the fresh soils, but response to added substrate were similar to or exceeded those of fresh soils. Our results suggest that relieving substrate limitation enabled the rebounded microbial community to respond to substrate additions similar to the community response in fresh soils. Ongoing enzyme assays and characterization of community composition before and after substrate addition will enable us to determine whether the long-term incubation caused a shift in the optimal temperature for enzymes function and community diversity. We believe that this work has important implications for understanding biological controls on SOM responses to climate change.
