Effects of heavymetal accumulationin apple orchard surfacesoils on the transformation processes of organic matter

研究了连续施用重金属农药对苹果园表层土壤重金属（Cu、Pb、As）积累对植物残茬分解及微生物生物量大小和活性的影响。实验结果如下：1。重金属在苹果园土壤中的积累对新鲜植物残体的分解没有抑制作用，而对腐殖化植物残体的分解有较大的抑制作用。2 .重金属在苹果园土壤中的积累降低了土壤有机质中微生物生物量的比例，增加了真菌生物量占总微生物生物量的比例。作为微生物活动指标的脱氢酶活性和土壤呼吸在重金属的存在下降低，当以土壤有机质为基础表示时。苹果园土壤重金属积累对植物残体分解、微生物生物量和微生物活性的毒性依次为Cu>>Pb>As。水溶性铜和交换性铜的含量与土壤pH值有关，对植物残体分解和微生物活性有不利影响，而苹果园表层土壤中微可溶性重金属的积累则对微生物生物量有不利影响。

The effects of heavy metals (Cu, Pb, As) accumulated in apple orchard surface soils associated with the continuous application of metal-based pesticides on the decomposition of plant residue and the size and activity of the microbial biomass were assessed. The results obtained were as follows :1.The heavy metals accumulatedin apple orchard soils did not inhibit the decomposition of fresh plant residues, while inhibited considerably the decomposition of humified plant residues.2.The heavy metals accumulated in apple orchard soils reduced the proportion of the microbial biomass in the soil organic matter and, further, increased the proportion of fungal biomass in the total microbial biomass.3.The dehydrogenase activity and soil respiration measured as indications of microbial activity were reduced in the presence of heavy metals, when expressed on a soil organic matter basis.4.The toxicity of the heavy metals accumulated in apple orchard soils was in the order of Cu>>Pb>As with respect to the plant residue decomposition, microbial biomass, and microbial activity.5.The plant residue decomposition and microbial activity were adversely affected by the water-soluble and exchangeable Cu whose amount depended on the soil pH,whereas the microbial biomass by the slightly soluble heavy metals accumulated in apple orchard surface soils.