Soil Microbial Ecology - Soil Molecular Ecology Laboratory

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E X E R C I S E
8
SOIL METABOLIC ASSESMENT
2. RESPIRATION / BIOMASS TESTS
RESPIRATION
OBJECTIVE:
Quantify soil microbial activities by measuring carbon dioxide production in treatments
of different carbon sources.
INTRODUCTION:
Respiration of microorganisms in soil was one of the earliest, and still is one of the most
frequently, used indices of soil microbial activity. Measurements of respiration have
been found to be well correlated with other parameters of microbial activity such as
nitrogen or phosphorus transformations, metabolic intermediates, and average microbial
numbers
Carbon comprises about 45 to 50% of the dry matter of plant and animal tissues. When
these tissues or residues are metabolized by microorganisms, 0 2 is consumed and C0 2 is
evolved in accordance with the following generalized reaction:
(CH 2 0) x + 0 2 ⎯⎯⎯⎯⎯⎯→ C0 2 + H 2 0 + intermediates + cell material + energy
In this reaction, all of the organic carbon should eventually be released as C0 2 . In actual
practice, under normal aerobic conditions, only 60 to 80% of the carbon is evolved as
C0 2 because of incomplete oxidation and synthesis of cellular and intermediary
substances. The quantities of C0 2 evolved depend on the type of carbon substrate, the
environmental conditions, and the types and numbers of microorganisms involved.