Abstract：
Soil chromium (Cr) contamination has become an environmental problem of global concern. However, the joint effects of combined utilization of biochar and arbuscular mycorrhizal (AM) fungal inoculum, which are considered as two promising remediation strategies of soil heavy metal pollutions, on plant Cr resistance are still poorly understood. In this study, a two-factor pot experiment was conducted to investigate how biochar and AM fungus Rhizophagus irregularis regulate Medicago sativa growth, physiological trait, nutrient and Cr uptake, relevant gene expressions, soil properties, and Cr speciation, independently or synergistically. The results showed that biochar notably decreased AM colonization, while biochar and AM fungus could simultaneously increase plant dry biomass. The greatest growth promotion was observed in mycorrhizal shoots at the highest biochar level (50 g kg-1 soil) by 91 times. Both biochar application and AM fungal inoculation enhanced plant photosynthesis and P nutrition, but the promoting effects of AM fungus on them were significantly greater than that of biochar. In addition, the combined application of biochar and AM fungus dramatically reduced shoot and root Cr concentrations by up to 92 % and 78 %, respectively, compared to the non-amended treatment. Meanwhile, down-regulated expressions were observed for metal chelating-related genes. Furthermore, Cr translocation from roots to shoots was reduced by both two soil amendments. Transcriptional levels of genes involved in reactive oxygen species and proline metabolisms were also regulated by biochar application and AM fungal colonization, leading to alleviation of Cr phytotoxicity. Furthermore, AM fungal inoculation slightly elevated soil pH but decreased plant-available soil P, which was, by contrast, lifted by biochar addition. The combined application reduced soil acid-extractable Cr concentration by 40 %. This study provides new insights into comprehensively understanding of the mechanisms of biochar and AM fungi combination on improving plant Cr tolerance.
摘要：
土壤铬（Cr）污染已成为全球关注的环境问题。然而,生物炭和丛枝菌根（AM）接种物联合利用的联合作用，被认为是两种有前途的土壤重金属污染修复策略，对植物Cr抗性仍知之甚少。在这项研究中,进行了双因素盆栽实验，以研究生物炭和AM真菌不规则根瘤菌如何调节紫花苜蓿的生长，生理特性，养分和Cr吸收，相关基因表达，土壤性质，和Cr形态，独立或协同。结果表明，生物炭显著降低AM定殖，而生物炭和AM真菌可以同时增加植物干生物量。在最高生物炭水平（50g/kg土壤）的菌根芽中观察到最大的生长促进作用，提高了91倍。生物炭的施用和AM真菌接种均增强了植物的光合作用和磷营养，但AM真菌对它们的促进作用明显大于生物炭。此外,生物炭和AM真菌的联合应用显着降低了芽和根Cr浓度高达92％和78％，分别,与未修正的治疗相比。同时,观察到金属螯合相关基因的表达下调。此外，两种土壤改良剂都减少了Cr从根到芽的转运。参与活性氧和脯氨酸代谢的基因转录水平也受到生物炭应用和AM定植的调节。从而减轻Cr的植物毒性。此外，AM真菌接种略微升高了土壤pH，但降低了植物有效土壤P，那是，相比之下,通过添加生物炭。联合施用将土壤酸可提取的Cr浓度降低了40％。本研究为全面理解生物炭和AM组合提高植物耐Cr性的机制提供了新的见解。
