生物炭复合菌剂对蔬菜种植园土壤细菌群落结构和氮组分的影响

A biochar composite bacterial agent affects the bacterial community structure and nitrogen composition in the soil of a vegetable plantation

摘要:

目的 蔬菜种植园土壤存在肥力退化、pH下降和重金属溶出等问题，需探究生物炭复合菌剂对菜园土壤细菌群落结构、氮组分和重金属有效性的作用机制。方法 以重金属抗性菌罗尔斯通氏菌(Ralstonia) Bcul-1 (R-B)和芽孢杆菌(Bacillus cellulasensis) Zn-B (BC-Z)与生物炭(biochar, BI)制备固定化菌剂，并将其添加到长期轮作番茄的菜园土壤(pH 5.6)中。基于土壤细菌高通量测序和土壤成分测定分析菜园土壤的细菌种群多样性、pH、氮碳含量和重金属化学形态，研究生物炭复合菌剂对土壤细菌群落结构、氮碳供给和土壤重金属活性的影响。结果 生物炭固定化促使外源菌R-B和BC-Z在重金属复合污染的菜园土壤中生长，并与土壤原有的高抗性Bacillus (10.18%-11.88%)长期共存，有效改善了土壤细菌种群结构、调整了差异菌群(biomarker)分布和增加了高丰度菌[如链霉菌(Streptomyces)、地嗜皮菌(Geodermatophilus)和类诺卡氏菌(Nocardioides)等]的相对丰度。此外，土壤细菌种群(属水平)、部分高丰度菌和外源菌R-B与土壤重金属化学形态和氮碳组分密切相关。添加生物炭菌剂(BI+R-B、BI+BC-Z和BI+R-B+BC-Z)后，菜园土壤的pH、EC、全氮、硝态氮(NO₃^--N)、有机质和总有机碳分别最高增加0.41、20.74%、18.96%、24.77%、10.26%和21.56%，且铵态氮(NH₄⁺-N)残留减少13.91%，维持了菜园土壤氮碳供给能力。R-B生物炭菌剂(BI+R-B和BI+R-B+BC-Z)减少了土壤重金属(Cd、Cr、Pb、Cu和Zn)的交换态、还原态或氧化态含量(减少0.18%-12.33%)，同时增加了其残渣态含量(增加0.16%-14.59%)，有效钝化了菜园土壤重金属活性。结论 生物炭复合菌剂(BI+R-B+BC-Z)改善了重金属复合污染的菜园土壤细菌群落结构，促进了R-B生长，增加了高丰度菌的相对丰度，并维持了外源菌R-B和BC-Z与土壤原有的高抗性Bacillus长期共存。同时，该菌剂提高了土壤的pH、EC、总氮、硝态氮、总有机碳和有机质，减少了铵态氮残留，钝化了土壤重金属(Cd、Pb和Cu)活性，有效调控了菜园土壤细菌群落活性、外源双功能菌生长、氮碳供给、pH和重金属化学形态，具备维持菜园土壤供肥能力和治理重金属复合污染的潜力。

Abstract:

Objective The soil in the vegetable plantation suffered from fertility degradation, pH decrease, and heavy metal leaching, necessitating the exploration of the mechanism by which composite bacterial agents regulate the bacterial community structure, nitrogen composition, and heavy metal availability in the vegetable plantation soil.Methods The heavy metal-resistant bacterial strains Ralstonia Bcul-1 (R-B) and Bacillus cellulasensis Zn-B (BC-Z) were prepared with biochar as an immobilized bacterial agent and then applied to the acidic soil (pH 5.6) of a vegetable plantation under long-term tomato rotation. High-throughput sequencing of soil bacteria and the determination of soil composition were conducted to analyze the bacterial diversity, soil pH, nitrogen-carbon content, and heavy metal chemical speciation, on the basis of which the effects of the biochar composite bacterial agent on the bacterial community structure, nitrogen-carbon supply, and heavy metal activity in the soil were analyzed.Results Biochar immobilization facilitated the growth of exogenous bacteria R-B and BC-Z in the vegetable plantation soil contaminated with heavy metals and maintained long-term coexistence of R-B and BC-Z with the original highly resistant Bacillus (10.18%-11.88%) in the soil. Accordingly, it effectively improved the bacterial community structure, adjusted the distribution of differential bacteria (biomarkers), and restoratively increased the relative abundance of abundant bacteria (such as Streptomyces, Geopathophilus, and Nocardioids) in the soil. In addition, soil bacterial genera, partial abundant bacteria, and the exogenous bacterial strain R-B were closely related to heavy metal chemical speciation and nitrogen-carbon components. The application of biochar bacterial agents (BI+R-B, BI+BC-Z, and BI+R-B+BC-Z) increased the pH, EC, total nitrogen, nitrate nitrogen, organic matter, and total organic carbon of the soil by up to 0.41, 20.74%, 18.96%, 24.77%, 10.26%, and 21.56%, respectively, while decreasing the ammonium nitrogen residue by 13.91%, maintaining the nitrogen-carbon supply capacity of the soil. BI+R-B and BI+R-B+BC-Z reduced the content of exchangeable, reducible, and oxidizable heavy metals (Cd, Cr, Pb, Cu, and Zn) by 0.18%-12.33%, but increased the residual content of these heavy metals by 0.16%-14.59%, effectively passivating heavy metals in the soil.Conclusion The biochar composite bacterial agent (BI+R-B+BC-Z) improved the bacterial community structure, promoted R-B growth, increased the abundance of abundant bacteria, and maintained the long-term coexistence of exogenous bacteria R-B and BC-Z with the original highly resistant Bacillus in the vegetable plantation soil with heavy metal compound pollution. Moreover, it increased soil pH, EC, total nitrogen, nitrate nitrogen, total organic carbon, and organic matter, while reducing ammonium nitrogen residue and passivating soil heavy metals (Cd, Pb, and Cu). Therefore, it effectively regulated the bacterial community activity, exogenous bifunctional bacterial growth, nitrogen-carbon supply, pH, and heavy metal chemical speciation, with the potential to maintain the fertilizer supply capacity and control heavy metal compound pollution of vegetable plantation soil.