不同水分管理模式下坡缕石修复稻田土壤镉污染效果

  目的  探究在合理的水分管理模式下提高坡缕石钝化稻田土壤镉的效率，及坡缕石施加对土壤理化性质、环境质量和水稻抗氧化胁迫的影响。  方法  采用盆栽试验方法，试验设置长期淹水、传统灌溉和湿润灌溉3种水分管理措施，每一水分管理模式下设0%、0.5%、1.0%、1.5%、2.0%和2.5% 6个坡缕石施加浓度，共18个处理，通过测定土壤pH、zeta电位、有效态镉、稻米生物量、稻米镉含量、土壤酶和叶抗氧化酶活性，分析不同水分管理措施与坡缕石用量组合修复镉污染的效果。  结果  长期淹水、传统灌溉和湿润灌溉下，坡缕石处理土壤pH分别增加0.49 ~ 1.24、0.49 ~ 1.47和0.42 ~ 1.64个单位，0.025 mol L?1 HCl提取态镉含量分别下降15.4% ~ 46.2%，11.5% ~ 39.7%和11.4% ~ 32.4%，毒性浸出法提取态镉最大降幅分别为47.4%、42.4%和40.2%（P < 0.05）。未施加坡缕石条件下，与传统灌溉比，长期淹水、湿润灌溉的稻米生物量降低11.2%和19.3%（P < 0.05）。3种水分管理模式下，坡缕石处理的稻米镉含量分别下降21.9% ~ 75.0%，17.8% ~ 70.2%和17.4% ~ 66.5%，土壤磷酸酶活性最大增幅分别为40.0%、57.1%和40.9%，叶超氧化物歧化酶活性最大增幅分别为33.9%、50.2%和37.4%（P < 0.05）。  结论  长期淹水下坡缕石钝化土壤镉的效率最高，1.0%坡缕石施加使稻米镉含量降至我国食品污染物含量限量标准0.20 mg kg?1（GB 2762—2012）以下，长期淹水联合坡缕石施加组合为镉污染稻田土壤修复技术。

Use of Palygorskite to Remediate Cd polluted Paddy Soils under Different Water Managements

  Objective  The water management model plays an important role in remediation of cadmium (Cd) polluted paddy soils. The reasonable water management regime is explored to promote the immobilization of Cd by palygorskite in contaminated paddy soils and investigate the effects of palygorskite addition on physicochemical property and environmental quality of soil and resistance of rice plant to Cd oxidative stress.   Method  There were totally 18 treatments in the pot experiment, which included 3 water managements of continuous flooding (5-7 cm surface water during the whole growth period of rice plant, with a scale line on the sidewall of pot), traditional irrigation (moist soil surface during the late tillering state and grain filling stage, and 5-7 cm surface water during the other growth stages of rice plant) and wetting irrigation (moist soil surface during the entire growth period of rice plant. The deionized water (2.3 kg) was added in the pot according to soil moisture content of 75% field water capacity and 8.0 kg of soil sample added in the pot) and six palygorskite treatments included the doses of 0, 0.5%, 1.0%, 1.5%, 2.0% and 2.5% in paddy soils. The effects of palygorskite addition on pH, zeta potential and contents of chemically extractable Cd (0.025 mol L?1 HCl extractable Cd and Toxicity Characteristic Leaching Procedure, TCLP extractable Cd) were determined in paddy soils, and biomasses and concentrations of Cd in brown rice were tested in the pot experiment, as well as the activities of enzymes in soils and antioxidant enzymes in leaves of rice plant.   Result  After the palygorskite was added to paddy soils, the pH increased by 0.49-1.24 units under continuous flooding, 0.49-1.47 units under traditional irrigation, and 0.42-1.64 units under wetting irrigation (P < 0.05). The absolute values of zeta potential in amended soils rose significantly. The contents of chemically extractable Cd in treated soils declined significantly, with reductions of 15.4%-46.2%, 11.5%-39.7% and 11.4%-32.4% for the 0.025 mol L?1 HCl extractable Cd and maximum decreases of 47.4%, 42.4% and 40.2% for the TCLP extractable Cd under 3 water managements (P < 0.05). In paddy soils untreated with palygorskite, the biomasses of brown rice reduced by 11.2% under continuous flooding and 19.3% under wetting irrigation in contrast to traditional irrigation (P < 0.05). The concentrations of Cd in brown rice in amended soils reduced by 21.9%-75.0% under continuous flooding, 17.8%-70.2% under traditional irrigation, and 17.4%-66.5% under wetting irrigation (P < 0.05). The activities of phosphatase in paddy soils amended with palygorskite under 3 water managements rose significantly with maximum increases of 40.0%, 57.1% and 40.9%, and the activities of superoxide dismutase (SOD) in leaves of rice plant upon palygorskite treatment increased by 33.9%, 50.2% and 37.4% maximally (P < 0.05).   Conclusion  The continuous flooding promotes the Cd immobilization by palygorskite in heavy metal contaminated paddy soils with a maximum reduction of content of chemically extractable Cd among 3 water managements. The 1.0% palygorskite treatment causes the concentration of Cd in brown rice lower than Chinese standard of 0.20 mg kg?1 (GB 2762—2012, Maximum permissible concentration of contaminants in food in China). The palygorskite addition combined with continuous flooding management, could be recommended as a practical measure for immobilization remediation of Cd-polluted paddy soils.