根际土壤中汞甲基化与去甲基化作用双同位素示踪研究

根际环境特殊的理化性质可能显著促进汞(Hg)的甲基化.为证实上述假设,本研究采集了三峡库区消落带狗牙根根际土和非根际土,分别测定了根际土与非根际土中总汞(THg)和甲基汞(MeHg)含量及主要理化性质,并采用双同位素示踪法(~(199)Hg~(2+)和Me~(201)Hg)进行室内模拟培养实验,探究其Hg的甲基化与去甲基化速率.结果表明,根际土壤中的Fe~(2+)、Mn~(2+)、有机质含量、过氧化氢酶活性显著高于非根际土(p0.05),MeHg含量、细菌、真菌数极显著大于非根际土(p0.01);根际土壤中MeHg的含量与Mn~(2+)、SO_4~(2-)、有机质含量存在显著正相关性(p0.05),与过氧化氢酶活性、细菌、真菌数存在显著正相关性(p0.01);根际土壤中Hg甲基化、去甲基化速率、净甲基化潜力均显著大于非根际土(p0.05),有菌根际土的甲基化与去甲基化速率显著大于无菌根际土(p0.05).本研究证实了根际是Hg发生甲基化的一个活跃区域,其中,微生物在根际土壤中Hg的甲基化与去甲基化过程中均起着主要作用.

Methylation and demethylation of mercury in rhizosphere soil by double isotope tracing

The special physical and chemical properties of the rhizosphere environment would significantly promote the methylation of mercury. In order to confirm this hypothesis, we investigated the concentration of total mercury (THg), methyl mercury (MeHg), and the critical physical and chemical properties in the rhizosphere soil of Cynodon dactylon and bulk soil in the water-fluctuating zone of the Three Gorges Reservoir Region (TGRR), and further used the dual-isotopic tracer method (¹⁹⁹Hg²⁺ and Me²⁰¹Hg) to determine the Hg methylation and demethylation rate of rhizosphere and bulk soil under different culture conditions. Results showed that concentrations of Fe²⁺, Mn²⁺, organic matter and catalase in rhizosphere soil were significantly higher than those in bulk soil (p<0.05), and specifically, the concentration of MeHg and the number of bacteria and fungi were significantly higher than those in bulk soil (p<0.01). Additionally, MeHg exhibits a significantly positive correlation to Mn²⁺, SO₄^2- and organic matter content in rhizosphere soil (p<0.05), and an extremely positive correlation to catalase activity, bacteria and fungi (p<0.01). Finally, the Hg methylation, demethylation rate and net methylation potential in rhizosphere soil were significantly greater than bulk soil (p<0.05), and the rate of methylation and demethylation in the rhizosphere soil were also significantly greater than sterile rhizosphere soil (p<0.05). This study suggests that the rhizosphere is an active region of Hg methylation, in which microbes play a major role in the methylation and demethylation of Hg.