Microbial Community Composition, Microbial Community Function, and Carbon and Nitrogen Dynamics in Soils Exposed to Chronic Warming and Nitrogen Additions
NSRC researchers investigated how soils respond to two threats of global environmental significance: climate warming and nitrogen deposition. Researchers examined how increased temperatures and nitrogen inputs affect soil microorganisms, such as bacteria and fungi, and the processes they perform. Because soil microbes are active in the Northern Forest under snowpack as well as during the summer months, researchers also assessed the soil's response to global change during the winter.
Researchers established a long-term soil warming and nitrogen fertilization experiment at the Harvard Forest Long Term Ecological Research site in Massachusetts. The experiment contained four different treatments: control, heated, nitrogen, and heated plus nitrogen. Since August of 2006, researchers have measured soil carbon and nitrogen changes and the soil microbial community. So far, soil warming has increased annual rates of carbon dioxide (CO2) respiration by soil microbes. Researchers estimate that as much as 17% of the increase in CO2 occurred during winter.
The treatments have had an early impact on the microbial community with differences in soil bacteria and fungi between the heated plus nitrogen and the control plots. Soil enzyme activity, associated with microbes, tended to be lower in nitrogen-fertilized plots; however, the activities of several plant litter degrading enzymes differ seasonally, with the highest rates in the summer and the lowest during the winter. These early results suggest that soils are active in winter, and global changes, such as climate warming and nitrogen deposition, can alter the soil microbial community and soil carbon cycling year-round.