Abstract: The transformation and renewal of amino acid enantiomers is of significance in indicating the turnover mechanism of soil organic matter. In this paper, a method of gas chromatogram/mass spectrometry combined with U-¹³ -C-glucose incubation was developed to determine the ¹³C-enrichment in soil amino acid enantiomers, which could effectively differentiate the original and the newly synthesized amino acids in soil matrix. The added U-^13-C-glucose was utilized rapidly to structure the amino acid carbon skeleton, and the change of relative abundance of isotope ions could be determined by mass spectrometry. The direct incorporation of U-¹³C glucose was estimated by the intensity increase of m/z (F+n) to F (F was parent fragment, and n was the carbon number in the fragment), while the total isotope incorporation from the added ¹³C could be calculated according to the abundance ratio increment summation from m/z (Fa+1) through (Fa+T) (Fa was the fragment containing all original skeleton carbons, and T was the carbon number in the amino acid molecule). The ¹³C enrichment in the target compound was expressed as atom percentage excess (APE), and that of D-amino acid needed to be corrected by the coefficient of hydrolysisinduced racemization. The¹³C enrichment reflected the carbon turnover velocity of individual amino acid enantiomers, and was powerful to investigate the dynamics of soil amino acids.

Key words: Pinus tabulaeformis plantation, closetonatural forest management, seedling regeneration, stand growth, species diversity, soil characteristics.