根施伯克氏菌对小麦镉吸收转运的两段式阻控作用

Two-stage Inhibition Effects of Burkholderia sp.Y4 Application on Cadmium Uptake and Transport in Wheat

为评估将伯克氏菌Y4(Burkholderia sp.Y4)作为污染农田小麦降镉(Cd)菌的可行性,通过微生物高通量测序、土壤Cd逐级提取、小麦Cd亚细胞分布和赋存形态检测等手段,分析了菌株Y4处理下根际土壤微生物群落和Cd有效态变化,以及小麦根、基节、节间和籽粒Cd含量及其转运特征.结果表明,根施菌株Y4显著降低了小麦根部和籽粒Cd含量,与对照处理相比降幅分别为7.7%和30.3%.小麦营养器官Cd含量及Cd转移因子结果显示,菌株Y4处理使Cd从基节向节间的转移因子降低79.3%,小麦节间Cd含量也随之降低50.9%.Cd赋存形态研究发现,菌株Y4处理增加了根和基节中残渣态Cd占比,降低了根系中无机态和水溶态Cd的含量,并提高了基节中残渣态Cd含量.进一步检测Cd的亚细胞分布发现,根细胞壁和基节细胞液中Cd含量增幅分别达21.3%和98.2%,可见菌株Y4处理提高了根细胞壁和基节细胞液对Cd的固定能力.深入研究根际土壤发现,菌株Y4处理使小麦成熟期根际伯克氏菌的相对丰度由9.6%提高至11.5%,并改变了土著微生物的群落结构,提高了Gemmatimonadales、Pseudomonadales和Chitinophagales等相对丰度,并降低了Acidobacteriota等相对丰度.同时,施加菌株Y4提高了根际土pH值,增幅达8.3%;降低了土壤中的可交换态Cd、碳酸盐结合态Cd和铁锰氧化物结合态Cd含量,其降幅分别达44.4%、21.7%和15.9%,而残渣态Cd比例高达53.6%.根施菌株Y4提高了土壤中硝态氮和铵态氮的含量,增幅可达22.0%和21.4%,并且碱解氮含量也有一定程度提高.由此可见,根施菌株Y4不但提高了土壤氮素可利用性,同时能够通过降低根际土壤中Cd有效性、提高小麦根和基节的Cd拦截固定能力,“两段式”阻控污染土壤中Cd向小麦籽粒的转运积累.故伯克氏菌Y4作为小麦降Cd促生菌剂具有一定的应用潜力.

In order to evaluate the feasibility of using Burkholderia sp.Y4 as a cadmium(Cd)-reducing bacterial agent in contaminated wheat fields,the changes in the rhizosphere soil microbial community and Cd available state,as well as the content and transport characteristics of Cd in the wheat root,basal node,internode,and grain under the treatment of strain Y4 were tested using microbial high-throughput sequencing,step-by-step extraction,subcellular distribution,and occurrence analyses.The results showed that root application of strain Y4 significantly reduced the root and grain Cd content of wheat by 7.7% and 30.3%,respectively,compared with that in the control treatment.The Cd content and Cd transfer factor results in wheat vegetative organs showed that strain Y4 reduced the Cd transfer factor from basal node to internode by 79.3%,and Cd content in the wheat internode stem also decreased by 50.9%.The study of Cd occurrence morphology showed that strain Y4 treatment increased the proportion of residual Cd in roots and basal ganglia,decreased the contents of inorganic and water-soluble Cd in roots,and increased the content of residual Cd in basal ganglia.Further examination of the subcellular distribution of Cd showed that the Cd content in root cell walls and basal ganglia cell fluid increased by 21.3% and 98.2%,respectively,indicating that the Cd fixation ability of root cell walls and basal ganglia cell fluid was improved by the strain Y4 treatment.In the rhizosphere soil,it was found that the microbial community structure was changed by strain Y4 application.Under the Y4 treatment,the relative abundance of Burkholderia increased from 9.6% to 11.5%,whereas that of Acidobacteriota decreased.Additionally,the relative abundance of Gemmatimonadales,Pseudomonadales,and Chitinophagales were also increased by strain Y4 treatment.At the same time,the application of strain Y4 increased the pH value of rhizosphere soil by 8.3%.The contents of exchangeable Cd,carbonate-bound Cd,and iron-manganese oxide-bound Cd in the soil decreased by 44.4%,21.7%,and 15.9%,respectively,whereas the proportion of residual Cd reached 53.6%.Root application of strain Y4 increased the contents of nitrate nitrogen and ammonium nitrogen in the soil by 22.0% and 21.4%,respectively,and the contents of alkaline nitrogen also increased to a certain extent.In conclusion,the root application of strain Y4 not only improved soil nitrogen availability but also inhibited Cd transport and accumulation from contaminated soil to wheat grains in a"two-stage"manner by reducing Cd availability in rhizosphere soil and improving Cd interception and fixation capacity of wheat roots and basal nodes.Therefore,Burkholderia Y4 has application potential as a Cd-reducing and growth-promoting agent in wheat.