氮素对苜蓿植物修复垃圾堆场镉-多环芳烃复合污染土壤及土壤细菌群落结构的影响

面向我国村镇垃圾存量治理的需求，非正规垃圾填埋场的治理是关键.但目前对富含氨氮的垃圾堆场重金属有机污染物复合污染土壤植物修复效率的研究尚少见报道.选取耐性植物紫花苜蓿，通过盆栽试验研究不同施N水平处理（0、10和50 mg ·kg^-1）对Cd-PAHs复合污染土壤植物生长、污染物的去除及土壤细菌群落结构的影响，以此评估N在植物修复垃圾堆场污染土壤过程中的作用.结果表明，高污染条件下［ω（Cd）为10 mg ·kg^-1和ω（PAHs）为400 mg ·kg^-1］，苜蓿生物量随施N水平的提高而增加，分别为不加N处理的6.0和6.3倍；低污染条件下［ω（Cd）为1 mg ·kg^-1和ω（PAHs）为100 mg ·kg^-1］，低N水平处理能促进苜蓿的生长，但差异不显著，而高N水平处理显著抑制其生长.植物修复中，苜蓿对低污染组中Cd的修复效率在5.58%~7.49%，N的添加显著提高高污染组中苜蓿修复效率，由0.95%提高至3.02%；与菲（Phe）相比，N对土壤中芘（Pyr）去除的促进作用更明显.此外，苜蓿可促进土壤中Phe和Pyr的去除，其中通过促进微生物对PAHs的降解作用占主导地位，而植物吸收作用的贡献小于0.21%.基于Bray-Curtis距离的冗余分析（db-RDA）显示PAHs和Cd是影响土壤微生物群落结构的主要因素，高N水平处理对单一Cd污染和高污染组中细菌群落分布影响更大，促进具有生物修复作用的菌属成为土壤优势细菌群落，如节杆菌属（Arthrobacter）、细杆菌属（Microbacterium）和新鞘脂菌属（Novosphingobium）等.研究结果可为我国垃圾堆场和非正规填埋场污染土壤生态修复提供理论依据.

Effect of Nitrogen on the Phytoremediation of Cd-PAHs Co-contaminated Dumpsite Soil by Alfalfa (Medicago sativa L.) and on the Soil Bacterial Community Structure

The key point in facing the demand for the disposal of waste storage in rural areas of China is to manage informal landfills. However, limited studies have been conducted to evaluate the phytoremediation efficiency of heavy metal and polycyclic aromatic hydrocarbon (PAHs) co-contaminated dumpsite soil with high ammonia nitrogen content. In this study, we selected the tolerant plant legume alfalfa (Medicago sativa L.) for a pot experiment to investigate the effects of nitrogen (N) (0, 10, and 50 mg·kg^-1) on plant growth, the removal of pollutants, and soil bacterial community structure in Cd-PAHs co-contaminated soil, so as to evaluate the role of N in the process of phytoremediation of dumpsite soil. The results showed that the biomass of alfalfa under high co-contamination conditions (Cd:10 mg·kg^-1 and PAHs:400 mg·kg^-1) increased with N supply and was 6.0 and 6.3 times higher than that of the treatment without N supply, respectively. Furthermore, the lower N level promoted the growth of alfalfa in the low-contamination group (Cd:1 mg·kg^-1 and PAHs:100 mg·kg^-1), but the difference was not significant, and a high concentration of N significantly inhibited its growth. In addition, the phytoremediation efficiency for Cd in the low-contamination group ranged from 5.58% to 7.49%, and N significantly increased the efficiency in the high co-contamination group from 0.95% to 3.02%. Compared with the removal of phenanthrene, N had a stronger influence on the removal of pyrene. Meanwhile, alfalfa could promote the removal of them in soil, among which the degradation of PAHs by microorganisms was dominant, whereas the contribution of the plant uptake pathway was less than 0.21%. As reflected by distance-based redundancy analysis (db-RDA), PAHs and Cd were the main factors affecting the structure of the microbial community; moreover, N had a greater effect on bacterial community composition in the single Cd-contamination and high co-contamination groups, promoting genera with bioremediation effects as the dominant soil bacterial communities, including Arthrobacter, Microbacterium, and Novosphingobium. This study will provide a theoretical basis for the remediation of dumpsites as well as informal landfills with contaminated soil.