M. Smith, K. Hofmockel, S. Bell, A.Thompson, E. Hobbie
Microbial activity plays an important role in decomposition as well as in carbon and nitrogen cycling. Microbial communities are also sensitive to change, and with increasing temperatures it can be expected that these microbes will show a response. Boreal peatlands are one of the largest carbon sinks on Earth, only covering about 3% of the Earth, but storing almost one third of the terrestrial carbon. One of the main mechanisms of decomposition can be seen in the extracellular enzymatic activity, specifically those enzymes important for breaking down carbon, nitrogen, and phosphorous. To study how increasing temperatures will affect microbial enzyme production, we examined extracellular enzymatic activity in Spruce and Peatlands Resources Under Climatic and Environmental Change (SPRUCE) site in the Marcell Experimental Forest of northern Minnesota. Microbial ingrowth peat cores were installed and microbial response to deep peat heating (up to +5°C above ambient) was evaluated. Ingrowth cores were installed in May of 2014 and extracted in June of 2015 (cores are composed of 10cm bags of 41 micron mesh to exclude roots, but allow fungal hyphae). Potential enzyme rates were measured in the hummock and hollow areas of the acrotelm in 10 cm peat increments from the peaks of hummocks to 30cm below hollow surface.
Overall, enzymatic activity was found to increase with increasing temperatures in carbon, nitrogen, and phosphorus degrading enzymes: beta-glucosidase, beta-xylosidase activity, and N-acetyl-beta-d-glucosaminidase (in unsaturated zone of hummocks) and cellobiohydrolase (saturated zone of hummock and hollow). While shifts can be seen across average measured temperature, significance could not be determined for this sample group, due to small sample size. Peptidase activity showed slight fluctuations with depth and temperature. We can conclude that enzymatic activity in response to warming was greatest at the surface, with some response to elevated temperatures.
Nitrogen, carbon and phosphorous degrading enzymes play a key role in the breakdown of organic matter; once material is broken down, nutrients are available to plants and other microorganisms. This positive feed back loop will only continue to increase and have greater effects on carbon and nitrogen cycling. Based on our results, increased warming could greatly influence nitrogen and carbon availability within these peatlands, which could have a harsh affect on the plant community in these ecosystems. Future responses will continue to be studied at the SPRUCE site.