Determination of low molecular weight dicarboxylic acids and organic functional groups in rhizosphere and bulk soils of Tsuga and Yushania in a temperate rain forest

Low molecular weight organic acids (LMWOAs) derived from root exudates, dec omposing organic matter, and other sources are important ligands. The speci es of these LMWOAs in the Tsuga rhizosphere soil (TRS), and Yushania rhizos phere soil (YRS), and bulk soil (BS) from an alpine forest region were iden tified. LMWOA and organic functional groups were used to those fresh twigs and leaves, litters, and roots as comparison. The objectives of this study were to (i) develop a method that could be used to determine LMWOAs in soil solution by gas chromatography (GC), (ii) assess methods for processing LM WOAs in soil samples, and (iii) determine the relative proportions of organ ic carbon functional groups in the TRS, YRS and BS, and fresh plant materia ls with C-13 nuclear magnetic resonance (C-13 NMR) analysis. The proportion of organic acid contents followed the order of YRS > TRS > BS, and also sh owed significant differences (P < 0.05) from GC analysis. The amounts of ma lonic, fumaric and succinic acids in the YRS samples were greater than in t he TRS and BS. Samples analyzed after 1 month of deep freeze storage (-24 d egreesC) showed no signs of decomposition. The proportion of organic functi onal groups in the rhizosphere and bulk soils quantified by C-13 NMR analys es followed the general order: alkyl-C > O-alkyl-C > N-alkyl-C > acetal-C > aromatic-C > carboxylic-C > phenolic-C.