Caitlin Buchheim, University Miami U of Ohio, BS

1. Get up off the couch!
How much of the soil microbial biomass is active?
Caitlin Buchheim, Mentor: Dr. Melany Fisk

2. Get up off the couch!
How much of the soil microbial biomass is active?
Caitlin Buchheim, Mentor: Dr. Melany Fisk
• Total microbial biomass is important as a nutrient pool
• The active fraction rapidly decomposes organic matter and returns nutrients to
soil nutrient pools
• It is said that 90% of the microbial community is dormant at any time
• Substrate-induced respiration (SIR) method compares the basal respiration (BR)
to the substrate-induced respiration
BR = respiration by the active microbes
SIR = respiration by all the microbes “awakened” in response to added glucose
• N and P availability can both influence the fraction of the microbial biomass
that is active
• Does N or P increase the active fraction of the microbial biomass?

3. Get up off the couch!
How much of the soil microbial biomass is active?
Caitlin Buchheim, Mentor: Dr. Melany Fisk
• Total microbial biomass is important as a nutrient pool
• The active fraction rapidly decomposes organic matter and returns nutrients to
soil nutrient pools
• It is said that 90% of the microbial community is dormant at any time
• Substrate-induced respiration (SIR) method compares the basal respiration (BR)
to the substrate-induced respiration
BR = respiration by the active microbes
SIR = respiration by all the microbes “awakened” in response to added glucose
• N and P availability can both influence the fraction of the microbial biomass
that is active
• Does N or P increase the active fraction of the microbial biomass?
BR:SIR indicates the relative fraction of total biomass that is active