Cu胁迫下土壤硝化功能的变化及其影响因素初探

随着养殖业的规模化发展，Cu、Zn等重金属元素作为饲料添加剂被广泛应用于畜禽养殖，并随着畜禽粪便的大量、广泛农用，Cu、Zn等低生物毒性的重金属元素在土壤中的逐渐累积以及污染问题日趋严重，这对土壤生态系统的稳定造成了严重的威胁。为探讨Cu胁迫下土壤生态功能的动态变化，文章采用室内模拟培养法，测定了红壤、黄土等8种典型土壤的潜在硝化势对Cu污染胁迫的时间效应；并利用统计分析手段研究了影响Cu胁迫下土壤的硝化功能恢复的主要因素。研究结果表明，在试验处理剂量下，Cu污染处理一周，各土壤潜在硝化势均受到完全抑制，即抑制率在80%以上；随着污染胁迫时间的延长，各土壤的硝化功能均有不同程度的恢复，且在540 d后，500 mg·kg-1 Cu处理土壤（除pH较低的红壤和黑土外）潜在硝化势的恢复率均达到其初始值的80%，即土壤硝化功能基本完全恢复；1000 mg·kg-1 Cu处理土壤（除褐土、棕壤和黄土3中土壤外）潜在硝化势的恢复率均显著低于80%。这表明Cu污染程度的增加可延迟土壤硝化功能的恢复。多元逐步回归分析表明，Cu 污染胁迫下土壤硝化功能的恢复与其初始硝化功能以及其对 Cu 耐受能力显著相关。由此可知，长期Cu污染胁迫下，土壤的硝化功能的恢复主要取决于土壤初始的硝化活性及其对Cu的耐受能力。

Primary Research on the Recovery of Soil Nitrification and Its Key Factors under the Cu Stress

Up to 90% of trace elements, such as Cu and Zn, that are fed to livestock are excreted and thus are present in manure. By the wide application of manure as fertilizer, these light toxic elements can reach soil, accumulate and cause serious risk on soils microbial ecology. The aim of this study is to determine the effect of Cu on soil nitrification function for a longtime after application, and its key factors. To this end, the soil potential nitrification rate （PNR） was determined, and the relationship between PNR and soil properties was tested. Eight soil samples, collected from 8 locations of China, were used to represent soil nitrification bacterial difference, and to assess s effects on the recovery of the soil nitrification to long time metal stress （Cu）. Soil （700 g） was amended with either mineral water and incubated in dark at 25℃ for 7 days. Then each of these soil treatments was mixed with CuCl2 solutions at two total concentration levels 500 mg kg-1 and 1000 mg kg-1, respectively. No Cu treated samples were selected as control treatments. After 0, 30, 180, 360 and 540 d, soils PNR were determined. At the same time, a spike-on-spike assay was set-up to test for tolerance of soil nitrification to copper （Cu）. The results indicated that all soil PNRs were seriously inhibited by Cu at the beginning, which was over 80 % for the soil samples treated with 500 mg·kg-1 and was 100 % for the soil samples treated with 1000 mg·kg-1. After a long time Cu exposure （540 days）, recovery of the soil nitrification rate were found in all the Cu amended soils, especially for the soils treated with Cu 500 mg·kg-1, PNR almost restored to the same level to the control treatments as the recovery rate ranging from 80% to 100%. Multiple steps regression analysis indicated that the recovery was strongly related to the soil primary nitrification activity and its initial tolerance to Cu. Increased Cu tolerance of soil nitrification was consistently observed in response to corresponding soil contamination,