Barak, P.
Molina, J.A.E.
Hadas, A.
Clapp, C.E.

Rival hypotheses, the mineralization-immobilization -turnover (MIT) hypothesis and the direct hypothesis, contend that deamination of soluble, low-molecular-weight nitrogenous compounds in soil is mediated by either extracellular or intracellular enzymes, respectively. To test these hypotheses, two amino acids, glycine (C/N=1.7) and leucine (C/N = 5.2), were added to an acid Hubbard loamy sand (sandy, mixed Udorthentic Haploboroll) and incubated for 7 d. Labeled 15N data, when analyzed using kinetic models reflecting either the direct or MIT hypotheses, reject the MIT hypothesis (~ = 0.01) and show evidence of direct incorporation of amino acids into the microbial biomass. -from Authors