Rhizosphere Chemistry of the Ta-Ta-Chia Forest Soils: Physicochemical Properties and Metal Speciation

H.T. Hu(1), M.K. Wang(1) and C.Y. Chiu(2)

(1) Dept. of Agri. Chem., National Taiwan University, Taipei, Taiwan;

(2) Institute of Plant Sci., Academia Sinica, Taipei, Taiwan

Abstract

The rhizosphere and bulk soils from A and B horizons under coniferous forest in the sites of the central mountain ridges of Taiwan were fractionated into clay (<2um), silt (2-50um), and sand (>50um) fractions, and analyzed for their pH, CEC, C and N contents, and metal speciation and bioavailability index. The 13-C NMR spectroscopy was used to investigate the nature of soil organic matter (SOM) in the various particle size fractions of the rhizosphere and bulk soils.

The organic C contents of the rhizosphere and bulk soils were in the range of 102~381 and 2-341 C/kg soil, respectively. The bulk soils were significantly lower than in total C contents and CEC than the rhizosphere soils; in contrast, the former were lower in pH than the latter. The particulate-bound species of Al, Fe, Mn, Cu and Zn and their bioavailability index values show a large variation which depended on the species of metals and rhizosphere and bulk soils. The 13-C CPMAS NMR data show that the intensity of signals assigned to carbohydrates (most O-alkyl C) and lignin (phenolic) decrease with decreasing particle-size in ehizosphere and bulk soils.