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通过培养实验,研究了70%田间持水量、干湿交替及淹水等3种水分管理方式对外源Hg在稻田土壤中甲基化的动态过程.外源添加浓度为5 mg·kg~(-1)Hg~(2+),培养时间为42 d.结果表明,70%田间持水量下,土壤甲基汞(Me Hg)含量基本保持稳定,平均为11.55μg·kg~(-1);淹水条件下,土壤Me Hg含量呈上升趋势,平均为30.70μg·kg~(-1),约为70%田间持水量的2.7倍;干湿交替条件下,土壤Me Hg呈现“涨-消”的波动趋势,平均含量为20.41μg·kg~(-1),约为70%田间持水量的1.7倍.培养结束后土壤Me Hg含量和占总Hg比例依次为:淹水(37.42μg·kg~(-1),0.76%)>干湿交替(16.08μg·kg~(-1),0.33%)>70%田间持水量(11.75μg·kg~(-1),0.25%),表明淹水条件有利于稻田土壤中汞的甲基化.Elovich方程可以拟合淹水条件下稻田土壤Me Hg含量变化的动力学过程,表明土壤中Me Hg含量在试验前期(7 d)快速升高,随后呈现缓慢增长的趋势.培养期间,各水分处理下稻田土壤中硫酸盐还原菌(SRB)数量均表现为上下波动式的周期性变化特征,均值分别为(533±31)cfu·g~(-1)(70%田间持水量)、(615±39)cfu·g~(-1)(淹水)和(509±43)cfu·g~(-1)(干湿交替).相关分析表明,土壤Me Hg含量与硫酸盐还原菌(SRB)数量、氧化还原电位(E_h)、土壤含水量之间的相关性达到了显著性水平(p<0.05),与其他因素之间无显著相关性.可以推测,在稻田土壤淹水形成的厌氧环境中,SRB可能是生物汞甲基化的优势菌群.
Through the cultivation experiment, the dynamic process of exogenous Hg methylation in paddy soil with 70% field water holding capacity, alternating wetting and drying and flooding was studied, and the effects of exogenous added concentration of 5 mg · kg ~ (-1) 1) Hg 2+, and the incubation time was 42 d.The results showed that the contents of MeHg in soil remained stable with an average of 11.55 μg · kg -1 under 70% field water holding capacity. Under flooded condition, the content of Me Hg in soil increased with an average of 30.70 μg · kg -1, which was about 2.7 times of that in 70% field. Under alternate dry-wet conditions, The average content was 20.41μg · kg -1, which was about 1.7 times of that of 70% field.The content of Me Hg and the proportion of total Hg in soil after flooding were as follows: flooding (37.42 kg · kg -1, 0.76%)> dry and wet alternations (16.08 μg · kg -1, 0.33%)> 70% field water holding capacity (11.75 μg · kg -1, 0.25%) , Indicating that flooding conditions are beneficial to the methylation of mercury in paddy soils.The Elovich equation can fit the dynamic process of Me Hg content in paddy soils under flooding conditions, indicating that the content of Me Hg in soil is fast at the early stage of the experiment (7 d) Increased, then showed a slow growth trend during cultivation, the water office The number of SRB in paddy soils varied with up-and-down fluctuations. The average values were (533 ± 31) cfu · g -1 (70% field capacity), ( 615 ± 39) cfu · g -1 (flooding) and (509 ± 43) cfu · g -1 (alternation between wet and dry) .Analysis showed that the contents of Me Hg in soil were similar to those of sulfate-reducing bacteria SRB), redox potential (E_h) and soil water content (p <0.05), and no significant correlation with other factors.It can be inferred that the formation of In anaerobic environment, SRB may be the predominant microbial biomembrane methylation.