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Harvard Forest Symposium Abstract 2016

• Title: Microbial respiration response to shifts in soil moisture in two forest types
• Primary Author: Jaclyn Matthes (Boston University)
• Additional Authors: Fiona Jevon (Dartmouth College); Ashley Lang (Dartmouth College); Mariko Whitenack (Dartmouth College)
• Abstract:

  Soil microbial communities are generally adapted to function best within the range of moisture conditions most commonly observed in their particular environments [1]. At the extreme ends of these ranges, desiccation and anoxic conditions can lead to microbial inactivity or death [2]. While some microbes can “acclimatize” to unfavorable soil conditions in the short-term, these responses are often energetically expensive [3,4]. Further, microbes adapted to wetter environments may not have the ability to maintain homeostasis in dry conditions, and microbes adapted to dry conditions may not be metabolically capable of respiring at higher rates given increased moisture [2]. Since climate projections for New England suggest shifts in the precipitation regime to less frequent, but more intense rainfall events [5], stressful moisture conditions may become increasingly common.
  
  To test how microbial respiration of wet and dry adapted communities respond to changes in their regular moisture conditions, we measured the carbon efflux (CO2) from soils subjected to laboratory manipulations of soil moisture. We collected soils from one deciduous and one hemlock stand on Prospect Hill in November 2015. Within each stand, we took cores at one moist, lowland location and one dry, upland location. In the lab, each sample was divided and treated with either the moisture conditions similar to those measured in their collection sites, or with the opposite moisture condition. We then measured respiration using an Ultra-Portable Greenhouse Gas Analyzer (Los Gatos Research). Measurements were taken daily over the course of seven days with moisture conditions in the samples kept constant during the testing period.
  
  These data will allow us to recognize short-term responses to either increased or reduced soil moisture, which may reflect acclimation (or a lack thereof) to novel moisture conditions within soil microbial communities. We expect that the lab moisture treatment will have the greatest effect on respiration rate, but that the microbial communities that regularly experience the treated moisture condition will respire at greater rates than those that don’t. We also hypothesize that over the course of the experiment the soil microbial communities will acclimate to their given moisture treatments and respiration will increase. Preliminary results suggest that (original) field moisture conditions do have an impact on the response of microbial communities to laboratory manipulations of soil moisture. Understanding how current soil moisture conditions may influence the response of soil microbial communities to changing moisture patterns will be important for predicting future ecosystem carbon fluxes.
  
  
  
  1. Fierer, N., Schimel, J. P. & Holden, P. A. Influence of drying-rewetting frequency on soil bacterial community structure. Microb. Ecol. 45, 63–71 (2003).
  
  2. Schimel, J., Balser, T. C. & Wallenstein, M. Microbial stress-response physiology and its implications for ecosystem function. Ecology 88, 1386–1394 (2007).
  
  3. Bradford, M. A. et al. Thermal adaptation of soil microbial respiration to elevated temperature. Ecol. Lett. 11, 1316–1327 (2008).
  
  4. Killham, K. & Firestone, M. K. Proline transport increases growth efficiency in salt-stressed Streptomyces griseus. Appl. Environ. Microbiol. 48, 239–241 (1984).
  
  5. Melillo, J. M., Richmond, T. C. & Yohe, G. W. (Eds). Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. 841 (2014). doi:10.7930/j0z31WJ2
  
  

• Research Category: Forest-Atmosphere Exchange
  Soil Carbon and Nitrogen Dynamics