老化生物炭对小白菜积累重金属的影响

Effect of aged biochar on the accumulation of heavy metals in pakchoi(Brassica chinensis L.)

[目的]生物炭对土壤中的重金属具有较强的吸附固定能力,能够降低重金属的植物可累积性。生物炭进入土壤后,在各种生物及非生物氧化作用下发生老化,而老化后的生物炭对土壤重金属的有效性以及对植物累积重金属的影响等方面的研究较少。[方法]本研究以氧化剂-干湿-冻融交替循环的方法对新鲜制备的生物炭(原始炭)进行老化,比较生物炭老化前后的阳离子交换量(CEC)、元素含量和表面官能团等参数的变化,并通过盆栽实验,探究生物炭老化前后对小白菜积累重金属(Pb、Cu、Cd)的影响。[结果]结果显示:与原始炭相比,老化作用能够增加生物炭的CEC、O/C值以及生物炭表面羟基和羰基的数量。相比未添加炭处理(对照组),老化炭的施用显著增加了土壤pH值和有机质含量(P<0.05)。而老化炭对土壤重金属有效态含量表现为显著降低,且施加量越大,效果越明显。即相比对照,5%老化炭处理下土壤中Pb、Cu、Cd的减少率分别为12.42%、11.67%、11.21%。相应地,老化炭的添加显著降低了小白菜体内重金属累积量(P<0.05),即未添加炭处理中小白菜体内Pb、Cu、Cd的含量分别为24.33 mg·kg^(-1)、28.8mg·kg^(-1)、0.2mg·kg^(-1),而在5%老化炭处理下小白菜体内Pb、Cu、Cd的含量各减少至3.33 mg·kg^(-1)、7.23mg·kg^(-1)、0.03mg·kg^(-1)。[结论]因此,老化生物炭依然能有效降低土壤重金属的生物有效性,说明生物炭对重金属污染土壤的修复具有一定的长期稳定性。

[Objective] Biochar has strong adsorption and fixation capacity to heavy metals in soil, which can reduce the accumulation of heavy metals by plants. Biochar undergoes oxidizing process under various biological and abiotic factors once it is introduced into soil. The oxidizing process makes the biochar aging which changes the physicochemical properties of biochar and thus influence the heavy metals availability in soil and the accumulation of heavy metals in plants, however, the research on this filed was much limited.[Methods] In the present study, the pristine biochar was aged by oxidant-drying/wetting-freeze/thaw alternating cycle method. The cation exchange capacity (CEC), element content and surface functional groups before and after biochar aging was compared. And pot experiment was set to investigate the aging effects on the accumulation of heavy metal (Pb, Cu and Cd) in pakchoi (Brassica chinensis L.).[Results] The results showed that aging increased the CEC, O/C value and the number of hydroxyl and carbonyl groups on the surface of biochar. Compared with the treatment without biochar addition (control group), the application of aged biochar significantly increased soil pH and the organic matter content ( P <0.05). However, the bioavailable concentration of heavy metals in soil was significantly reduced by adding aged biochar. And the reducing effect was more obvious with the increasing of biochar application rate, that is, the concentration of Pb, Cu and Cd in soil decreased by 12.42%, 11.67%, 11.21% for aged biochar with 5% application, respectively, compared to the control. Accordingly, the accumulation of heavy metals in the pakchoi was also significantly reduced by addition of aged biochar ( P <0.05). Consequently, the contents of Pb, Cu and Cd in pakchoi without biochar treatment were 24.33 mg ·kg^-1 , 28.8 mg ·kg^-1 , and 0.2 mg ·kg^-1 , respectively, whereas those were markedly decreased to 3.33 mg ·kg^-1 , 7.23 mg ·kg^-1 , and 0.03 mg ·kg^-1 under 5% aged biochar treatment.[Conclusion] Therefore, the aged biochar still effectively reduced the bioavailability of heavy metals to plants which is important to evaluate the long-term application of biochar in remediation of heavy metal polluted soil.