Abstract: The purple soils collected from four land-use types, including tea garden, dry land, paddy field and woodland in the Mingshan River watershed, were used to investigate the effect of purple soil aggregate components on the adsorption and desorption of Pd²⁺ by aggregates using the isothermal adsorption method of equilibrium and the desorption method of NH₄OAc and EDTA. The results showed that before and after removing organic matter, the absorbance of Pd²⁺ by differently sized aggregates increased with the initial Pd²⁺ concentration, in a sequence of (<0.002 mm) > 2-0.25 mm > bulk soil > 0.053-0.002 mm > 0.25-0.053 mm. The Freundlich equation was the best to fit the adsorption pattern. The distribution coefficient K_d was negatively correlated with the initial Pb²⁺ concentration. Woodland soil showed the maximum capacity of Pb²⁺ adsorption while tea garden soil showed the minimum. The adsorption was mainly based on electrostatic adsorption, supplemented by complexation adsorption. The nondesorption rate was in order of woodland > dry land > paddy field > tea garden, indicating that the holding capacity of the tea garden soil was the weakest and woodland soil was the strongest. After removing the organic matter, the Pd²⁺ absorbance by differently sized aggregates all decreased. The adsorption reductions of woodland and dry land soils were more obvious compared with those of tea garden and paddy soils. The reduction of maximum adsorption had a significant positive correlation with the amount of organic matter removal. In purple soils of the four landuse types, NH₄OAc desorption rate increased obviously while EDTA desorption rate decreased accordingly, and the nondesorption rate decreased in varying degrees.

Key words: diet composition, feeding change, trophic level, feeding intensity, Solenocera melantho