酸性矿山废水污染的水稻田土壤中重金属的微生物学效应

Effects of heavy metals on microbial biomass and activity in subtropical paddy soil contaminated by acid mine drainage

采样调查了广东大宝山地区受酸性采矿废水长期污染的亚热带水稻田的土壤理化性质 ,重金属 Cu、Pb、Zn、Cd的全量及其 DTPA浸提量 ,以及微生物生物量及其呼吸活性等指标。利用主成分和逐步回归分析了影响土壤重金属的有效性及其微生物学效应的因素。结果表明 :土壤高含硫 ,强酸性 ,有机碳、全氮较低 ,4种金属的全量普遍超标。DTPA可提取态金属含量较高 ,不仅与其全量呈显著正相关 ,而且与土壤酸度和粘粒含量正相关 ,和 Mn含量负相关。过量的金属显著降低了土壤微生物生物量 C、N、微生物商、生物量 N/全 N比 ,并抑制了微生物呼吸强度和对有机碳的矿化率 ,导致了土壤 C/N比的升高。同时 ,金属对微生物群落及生理代谢指标 ,如微生物生物量 C/N比和代谢商的影响不显著。 DTPA可提取态金属 ,特别是 DTPA- Cu是导致微生物生物量和活性指标变化的主要因素。以有机碳 (或全氮 )为基数的复合微生物指标降低了土壤性质差异造成的干扰 ,较单一指标更能准确指示微生物对金属胁迫的反应。土壤硫没有对金属有效性和微生物指标产生明显影响 。

Soil samples were collected from long-term metal-contaminated rice field in Dabao Shan area of Guangdong province, China. Soil physico-chemical properties, total contents and DTPA extractable fractions of Cu, Pb, Zn and Cd, and microbial biomass and organic carbon mineralization were investigated to analyze their relationships. Principal component analysis and stepwise regression were employed to characterize availability of heavy metals, microbial responses and their effect factors in the studied soil. The results showed that irrigation with acid mine drainage since end of 1960s resulted in high sulfur content, strong acidity, relatively low organic carbon and total nitrogen, as well as high contents of heavy metals and their DTPA extractable fractions. DTPA extractable metals were not only influenced principally by their total contents, but also were positively related to soil acidity and clay contents, and were negatively correlated with soil Mn contents. Excessive heavy metals remarkably reduced soil microbial biomass carbon, biomass nitrogen, ratio of biomass carbon to organic carbon and ratio of biomass nitrogen to total nitrogen. Metals also inhibited microbial respiratory activity and rate of mineralization of soil organic carbon, finally led to increase in soil C/N. In contrast, elevated heavy metals did not significantly influence microbial biomass C/N and metabolic quotient (qCO_2), which are considered as parameters of microbial community composition and physiological metabolism. Stepwise regression indicated that DTPA extractable metals, especially DTPA-Cu, were major factors affecting microbial biomass and carbon mineralization, rather than total contents. Apart from close relationship between metals and microbial indices, some soil physico-chemical characteristics, such as organic carbon and total nitrogen, were highly associated with microbial biomass carbon, nitrogen and soil basal respiration. Some linked microbial indices including ratio of biomass carbon to organic carbon, ratio of biomass nitrogen to total nitrogen, and CO_2 evolution per unit organic carbon, can decrease the blurring effect of soil spatial variability on study of metal stress. Our results further showed that metal indices were involved in regression models of influencing factors of such linked parameters, while most of soil physico-chemical parameters were eventually excluded from the models. It demonstrates that these linked indices could serve as microbial indicators of metal stress. In addition, soil sulfur did not show pronounced effect on availability of metals and change in soil microorganism. However, oxidation of sulfide was regarded as important cause of metal ion loose and acidification. Soil physico-chemical characteristics may indirectly influence microbial biomass and carbon mineralization through their effects on availability of heavy metals.