Samuel T. Dunn 1, 2 , Andrew G. Bunn 3 , John D. Schade 1

1. Response of soil microbial respiration to varying temperature and moisture in three soils from the Siberian Arctic B31G-0395 Samuel T. Dunn 1, 2, Andrew G. Bunn 3, John D. Schade1 1. Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, United States. 2. Biology, St. Olaf College, Northfield, MN, United States. 3. Environmental Sciences, Western Washington University, Bellingham, WA, United States Introduction: The mean annual temperature of the arctic is warming at a faster rate than the rest of the world. This warming will have effects on multiple ecosystem properties including soil temperature, soil moisture content, active layer depth, and plant community composition. What is uncertain is how these interactive properties will affect soil respiration. The permafrost soils of the arctic are estimated to contain over 1600Pg of C which is more than the atmosphere currently holds. (Schuur, E. A. G., J. Bockheim, et al., 2008) so any major change in decomposition and microbial respiration rates will have major implications for the global climate. Question: How will the soil respiration rate of different ecosystems in the arctic respond to changes in temperature and moisture? Discussion: Pleistocene Park: This site is a grazed pastureland that was converted from taiga forest after 1988. Rates of soil respiration increased due to higher temperatures but were unaffected by changes in soil moisture content (Figure. 1). Interestingly, the strength of temperature’s effect (the β value) was an order of magnitude lower than the Taiga (Table. 1). This apparent decrease in sensitivity to temperature may be indicative of a change in the microbial community after the conversion to pasture. The overall rates of soil respiration in Pleistocene Park were higher than the taiga. This difference in respiration rates is likely due to larger soil nutrient pools or the increased lability of compounds within the soil that resulted from the introduction of new plant species and grazers. The Taiga: Soil respiration rates in taiga soils increased with temperature but were not significantly influenced by soil moisture (Table. 1). It may be possible that the moist acidic environment of the taiga soil is home to a microbial community that is well adapted to moist conditions but is temperature limited. The Tundra: Soil respiration rates in the tundra were roughly equal to those in the taiga (Figures. 2,3). The sensitivity to change, however, was an order of magnitude greater for both soil moisture and the interaction between soil moisture and temperature (Table. 1). Unlike the Taiga or Pleistocene park, there was a marginally significant response in respiration to changes in soil moisture. The tundra has harsher growing conditions than either of the other 2 sites so this strong response may simply be the result of environmental inhibition that was alleviated by this study. Figure. 2 Rates of soil respiration increase as a function of both temperature but not moisture in soil from Taiga forest. There is a significant interaction effect between soil moisture and temperature (Table. 1) Figure.1 Rates of soil respiration increase as a function of temperature but not of moisture in a grazed grassland. There is a significant interaction effect between temperature and moisture (Table. 1) • Methods: • Samples were collected from 3 locations near the North-East Science Station in Siberia: a) tundra, b) taiga, and c) grazed pasture (Pleistocene Park). • Soils were sieved and homogenized to 2mm and a subset analyzed for % ash-free drymass , % gravimetric water content , and water holding capacity. • Soils were placed in mason jars and were modified to be at approximately 25, 50 and 75% water holding capacity (Diagram. 1) • The jars were placed in locations across a range of temperatures to incubate for 48hours. • Flux measurements were taken after 2, 24, and 48 hours by removing a series of headspace samples. • Temperature loggers recorded temperature every 5 minutes. • Loss of soil water was calculated via mass lost over time. Table.1 Multiple linear regression analysis reveals that temperature stimulated respiration the most. Moisture generally did not have any significant effect on respiration. The interaction between temperature and moisture increased soil respiration rates significantly. Figure. 3 Rates of soil respiration significantly increase as a function of temperature and marginally as a result of moisture in tundra soils. There is a significant interaction between soil moisture and temperature on respiration (Table. 1) Take Home Points: When exposed to similar conditions in the lab, soils from different communities responded to changes in unique ways. When taiga is converted to pasture, the metabolic response of the soil’s microbial community to change is muted. Interacting ecosystem characteristics have a significant effect on soil respiration. Characterizing these interactions is key to understanding how the arctic will change as the climate warms. Diagram. 1 Conceptual schematic of the experimental design used for each site I would like to thank all the members of the Polaris Project for their assistance in the collection of data. Thank you to Becky Tachihara for her photos. Special thanks to the staff of the North East Science Station for hosting this project. Funding for this project was supplied by a grant from the National Science Foundation Office of Polar Programs. Travel funds were graciously provided for by the Polaris Project and Colorado State University. Pleistocene Park Taiga Tundra