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ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Publications at this Location » Publication #222655

Title: Laboratory Assay of Soil Microbial Activities is Congruent with In Situ Conditions

item Lehman, R - Michael

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2008
Publication Date: 6/1/2008
Citation: Lehman, R.M., Garland, J.L., Frey, S.D. 2008. Laboratory Assay of Soil Microbial Activities is Congruent with In Situ Conditions. 108th General Meeting of the American Society of Microbiology, Boston MA, June 1-5, 2008.

Interpretive Summary:

Technical Abstract: We used microtiter plates loaded with an oxygen-sensitive fluorophore to assay respiration of organic substrates by soil microbial communities. The respiration of soil slurries was measured at low substrate concentrations (0.5 mg substrate per g soil) with no additional nutrients over a short seven hour incubation period in the lab. A month-long field study was conducted in which replicate 1 m2-plots received weekly amendments of either glucose or casamino acids (two application rates: 0.6 and 0.006 mg substrate per g of soil) or no carbon source (control). Soil samples were collected from all plots before and after each amendment and inoculated into the fluorophore-containing microtiter plates with the following substrates: none, glucose, mannose, sucrose, asparagine, glutamic acid, lysine, and casamino acids. Six days after the first amendment and one day before the second amendment, no significant effect of field treatment on measured activities could be detected; but, significant effects were detected one day following the second amendment and both one day before and one day after the last amendment. At these intervals, the respiration of all carbon sources was stimulated by the higher level of casamino acid treatment and the respiration of only the amino acid substrates was stimulated by the higher level of glucose treatment. Substrate respiration for the lower levels of both casamino acid and glucose treatments was equal to that of control plots. These results demonstrate that lab-measured activities reflected known in situ conditions and that the responses were consistent with the low ambient nitrogen levels measured in the field plots.