Microbial activity plays an important role in decomposition and influences elemental cycling in soil. These organisms are sensitive to environmental shifts, and are expected to respond to ecological change. A major mechanism of decomposition in soil can be measured in the extracellular enzymatic activity of microbes, specifically those enzymes important for breaking down carbon (C), nitrogen (N), and phosphorous (P). Peatlands cover about 3% of the Earth’s are terrestrial surface, but store almost one third of the C. These systems are cold, wet, and very nutrient limited, resulting in a buildup of non-decomposed plant material where C is stored. To study how ecological change could affect microbial enzyme potential, we examined extracellular enzymatic activity in the Spruce and Peatland Responses Under Changing Environments (SPRUCE) site in the Marcell Experimental Forest of northern Minnesota. To evaluate inputs of microbes, fungal ingrowth cores were used to assess microbial community responses to temperature and CO2 treatments (with temperature treatments ranging from +2.25 to +9°C above ambient and CO2 +500ppm above ambient). Samples were collected in June of 2015, after 11 months of initial below ground warming (Deep Peat Heat, DPH), and in August 2016, with 14 months of DPH, 11 months of above ground heat, and 2 months of elevated CO2 (Whole Ecosystem Warming, WEW).
Results/Conclusions
Potential enzyme rates were measured at 10cm increments of the surface of hollow and hummocks of the acrotelm. C, N, and P linked enzymes showed significant responses to changes in temperature and CO2. These responses varied significantly from hummock to hollow at corresponding depths, showing the importance of understanding the microtopography of these systems. Initial responses to DPH showed an increased potential with warming in C linked enzymes. However, after WEW, responses declined without elevated CO2. This trend was consistent across microtopography, though intensity was variable. N linked enzymes showed a general decrease with increased warming, implying that the microbial communities aren’t putting as much energy towards N acquisition as expected. This decrease in activity was shown to be strongest in the -20-30cm depths of the hollows and was seen with DPH and WEW. P linked enzymes showed an increase at all depths, except within -20-30cm, where a non-linear response was shown. Based on our results, microbial communities are affected by elevated temperatures and CO2, which could change how they store or utilize C in peatlands.