生物炭对水稻吸收重金属的阻控效应及生态机制

Heavy metal contamination of soil and farm product continues to be the focus of numerous environmental studies and attract a great deal of attention worldwide. Therefore, it's of significance in development of a variety of technologies to remediate heavy metal contaminated soils and to prevent heavy metals from entering food chain. Biochars are able to complex metal ions on their surfaces and therefore reduce bioavailability, which renders a reduced risk. With indoor simulation experiments, pot-culture experiments combined with field studies, this project will carry out research on the effects of biochar, produced by pyrolysis of rice-straw, on immobilizing soluble cadmium and lead in soil, and effects on the fractionations and biological characteristics of metals in soil-plant ecosystem. The overall goal of this proposal is to test the effectiveness of biochar soil amendment for reducing the bioavailability and phytotoxicity of Cd and Pb in field soils. The specific objectives of this research are to: 1) Determine effects of biochar on fate and transport of Cd and Pb in different soil types, and reveal the influence factors of pH, ionic strength; 2) Test effects of biochar on the soil-plant micro-interfaces of Cd and Pb in soils during different growth stages of paddy rice; 3) Assess the characteristics of soil micro-ecological environment in rhizosphere and non-rhizosphere region of paddy rice induced by biochar, with PCR-DGGE and BIOLOG techniques. Results obtained from this study are expected to provide greater understanding of processes with regard to immobilization remediation of Cd and Pb contaminated field soils, and thus realize remediation along with production in contaminated farmland and guarantee for agricultural sustainable development and agriculture product safety.

重金属是农田土壤和农产品中的一类重要污染物，深入开展土壤重金属污染修复技术研究，阻控有毒重金属进入食物链，对于恢复污染土壤生态服务功能，保障农产品安全和人体健康具有重要意义。本项目针对目前国内外生物炭在土壤重金属污染修复中的研究现状，以生物炭对土壤Cd、Pb的根际迁移及生物学过程为切入点，采用实验室模拟和野外大田试验相结合的方法，研究生物炭对Cd、Pb在不同类型土壤中的环境行为、影响因素及其对水稻吸收Cd、Pb的阻控效应；结合PCR-DGGE技术及BIOLOG微平板分析方法探索生物炭对水稻根际与非根际土壤微生物群落结构和功能多样性的影响特征。通过以上研究，阐明生物炭对土壤-水稻系统中Cd、Pb迁移转化规律，揭示生物炭对土壤微生物的分子生态学影响机制，以期为我国重金属复合污染原位修复提供重要的理论依据。

本项目采用室内土壤培养实验和野外大田实验相结合的方法，研究了生物炭对不同土壤类型重金属污染行为、影响因素及农作物吸收重金属的阻控效应。在野外大田实验中，主要对普遍存在的镉污染土壤进行了田间小区试验。通过3年的研究，获得了生物炭对土壤重金属镉污染钝化修复效应及其对土壤养分、酶活性和微生物群落结构多样性等的影响行为。（1）吸附试验表明，生物炭对Cd离子的吸附可以用Freundlich等温线进行拟合，在不同温度下其饱和吸附量分别为9.738 mg/g（288.15 K）、10.14 mg/g（298.15 K）、10.40 mg/g（308.15 K）、10.71 mg/g（318.15 K）；XPS分析表明生物炭对Cd的化学吸附机制主要为表面羟基（-C-OH）与羰基（-C=O）与Cd离子发生络合化学反应作用。（2）大田试验表明，低（5 t/ha）、中（10 t/ha）、高（20 t/ha）三种处理，与对照相比，油麦菜可食部分Cd含量降低32.6-54.8%，根部Cd含量降低14.4-30.9%。（3）经过不同的钝化处理后，水稻根、茎、叶、稻壳和稻米的镉含量分别降低了4.36-17.57%、17.69-32.31%、5.51-22.79%、5.88-41.76 %和37.70-73.77%；水稻茎、稻米Cd含量与土壤有效态Cd的相关性都达极显著水平。（4）与对照相比，各试验处理中，土壤脲酶、过氧化氢酶、酸性磷酸酶活性均有所提高，增幅分别70.28-231.87%、15.38-31.59%、89.51-152.45%；土壤有效态Fe、Mn、Cu、Zn的含量增幅依次为40.45-271.94%、51.68-322.34%、5.75-62.09%、63.67-1378.54%；土壤NH4+-N、NO3-N的活性、有效P、速效K、有效Mg及有效Ca的含量增幅分别为44.82-70.53%、8.69-52.55%、19.31-81.04%、50.01-622.24%、26.13-369.71%、73.28-522.69%。（5）土壤的微生物丰度较对照有所提高，相似性指数和聚类分析均显示，低用量生物炭施入土壤对土壤微生物群落的影响较小，随着生物炭用量的增加，DGGE指纹图谱中条带数量和亮度增加，会对土壤微生物群落结构多样性产生一定的影响。