Above and belowground impacts of climatic warming drive rates of decomposition in a grassland ecosystem
Climatic warming has the potential to alter rates of decomposition in terrestrial systems. However, the mechanisms by which warming may regulate carbon dynamics and overall storage are diverse. Aboveground, warming has the potential to alter plant community composition while belowground climate change may drive shifts in the composition of the microbial community, both of which have the potential to alter rates of decomposition. Data from a fourteen-year temperature manipulation in a tallgrass prairie reveal shifts in the belowground microbial community, as well as shifts in the relative abundance of the two most abundant grasses, Schizachyrium scoparium (little bluestem) and Sorghastrum nutans (Indian grass). Through two lab incubation experiments, we sought to understand how these biotic shifts might alter rates of plant litter decomposition in this ecosystem. In one experiment we varied the proportions of little bluestem and Indian grass and examined rates of decomposition. In a second experiment, we examined rates of litter decomposition on soils derived from warmed and control plots in the fourteen-year grassland warming experiment, incubated with a common substrate (little blue stem litter) under warmed and control lab conditions in a fully factorial design.
We find that shifting biotic communities, both above and belowground, likely play a role in altering rates of decomposition as a consequence of climatic warming. Specifically, as we increased the proportion of Indian grass relative to little bluestem, rates of decomposition decreased in our lab incubations. Further, while decomposition was generally higher under warmed lab conditions, we also observed a strong effect of soil origin on rates of decomposition, with higher decomposition on soils derived from warmed field plots. Together, these results suggest that changes to the biotic community, both above and belowground, are likely altering rates of decomposition. In our system, warming-induced changes belowground seem to increase rates of decomposition, while changes to plant communities aboveground may slow decomposition.