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Low-molecular-weight organic acids (LMWOAs) derived from root exudates and complexed with available metals in the rhizosphere soils of Taiwan red cypress (Chamaeyparis formosensis, FRS), peacock pine (Cryptomeria japonica, JRS), and moso bamboo (Phyllostachys pubescens, PRS) were identified by gas chromatograph (GC). The fresh plants (i.e., leaves, stems, roots, and litters) and soil samples of those three vegetations were examined for their organic functional groups. This study focused on (1) assessing methods for processing LMWOAs in the rhizosphere soils and fresh plants by GC analysis and (2) determining the relative proportions of organic carbon (C) functional groups in the three vegetations and fresh plant materials with 13C nuclear magnetic resonance (NMR) analysis. The proportion of LMWOAs contents followed the order of PRS>FRS>JRS>bulk soils. The recovery and spiking tests analyzed by GC showed good recovery (>83.6%) and reproducibility of LMWOAs. The proportion of organic functional groups in the rhizosphere and bulk soil quantified by 13C NMR analysis followed the general order alkyl-C>aromatic-C>O-alkyl-C>N-alkyl-C>phenolic-C>acetal-C>carboxyl-C. The carbohydrates, hemicellulose, lignin, and cellulose contents obtained by 13C NMR analysis suggested that Phyllostachys pubescen (PB) cannot easily be decomposed under the mountain forest soil environments. [ABSTRACT FROM AUTHOR]