Getting the Dirt on Soil Respiration


Sara Wilson and Ariel Tellatin


CU Fall 2006


          We questioned whether microorganisms would be more prevalent or active in some areas versus others and how soil respiration would compare and contrast in samples from three distinct ecological niches. Although easily overlooked, decomposers are the vital chemical recyclers of our planet without which, chances for all other life surviving would be slim. Therefore, the health of our soil is a major concern and we hypothesized soil respiration depends primarily upon water content and available organic matter.


         Three soil samples were collected at a 2-3” depth from each of three distinct niches: coniferous forest, agricultural field and ponds/creek.  Containers were airtight to maintain water content and opened every 6 hours for 3 minutes to replenish with fresh oxygen.  All were refrigerated and kept in the dark to subdue exponential microbial growth due to temperature and eliminate possible photosynthetic activity by live plant matter.  Samples were brought to room temperature, weighed and placed in a foil wrapped chamber attached to a CO2 probe.  Each trial consisted of a 3 minute stabilization period and 10 minute collection of data.  We predicted the ponds/creek to have the highest rate of respiration but, were uncertain how the forest and field would compare.


         Results indicated there was no significant difference between the forest (mean = 0.2313 ppm CO2/min/g), field (mean = 0.5300 ppm CO2/min/g) and ponds/creek (mean = 0.9987 ppm CO2/min/g) however, the P-value contrasting the forest to field was marginally significant at t = -0.789, P = 0.067 > 0.05.  A 3-4” layer of snow melt on the harvested, and therefore nutrient rich as opposed to nutrient absorbing, corn field in addition to a probable lack of recent pesticide spraying may have elevated respiration considerably.  Its’ muddy, clay-like consistency contrasted sharply with the damp, “potting-soil” quality of the forest floor.  One sample from our ponds/creek contained a relative overabundance of organic matter and, tested so much higher than the others, we believe it skewed any comparisons to the niche overall.


 Further tests would be necessary to determine more accurate distinctions but, we believe results indicate water content and available organic matter are primary determinants as hypothesized. Comparisons to other student projects were limiting but, a significant result by Wynn et al. 2001 revealed, after adding water to all their samples, respiration under conifers to be greater than under deciduous trees.


It would be interesting to compare and contrast data from agricultural field samples at various times throughout the year to test for microbial response to pesticides, fertilizers and nutrient variations at differing stages of plant growth.  Also, the amount of water in the soil would vary, as would temperatures.  To see the changes in respiration as different variables are isolated would help determine how mans’ intervention may be causing serious disruptions.  Contrasting organic versus industrialized agriculture would be even more intriguing and may give us clues as to how to rectify resulting problems.