镉胁迫对桑树根际细菌群落及其多样性的影响

Effects of Cd Stress on Bacterial Community Composition and Diversity in Mulberry Rhizosphere Soil

为探究镉(Cd)胁迫对桑树根际细菌群落及其多样性的影响,以桑树品种粤桑11号为供试植物,设置3种Cd胁迫浓度(5、3、2 mg/kg)模拟现实镉污染重度、中度和轻度水平,并以无Cd胁迫为对照进行盆栽试验,分析根际土壤细菌多样性和群落特征变化。结果显示,轻度镉污染胁迫下桑树根际土壤细菌ACE值、Chao1指数和Shannon指数最高,而Simpson指数最低;重度镉污染胁迫下桑树根际土壤细菌ACE和Chao1指数、Shannon指数最低,而Simpson指数最高。桑树根际土壤细菌分布在21个门,以放线菌门和变形菌门为主要优势菌门,占比分别为31.34%~62.60%和19.64%~34.82%,其中Cd胁迫处理特有细菌属于杂食菌门和迷踪菌门。冗余相关分析(RDA)显示,桑树根际细菌群落结构与环境因子存在显著相关,其中优势菌门变形菌门与土壤有机质(SOM)、全氮(TN)、全钾(TK)含量呈显著正相关,但与铁锰还原态Cd(FMO-Cd)、残渣态Cd(RES-Cd)和可交换态Cd(EXC-Cd)含量呈显著负相关,放线菌门与TK含量呈显著正相关,但与碳酸盐结合态Cd(CAB-Cd)和RES-Cd含量呈显著负相关。结果表明,低浓度Cd胁迫可提高桑树根际细菌群落多样性,而高浓度Cd胁迫会抑制桑树根际细菌群落多样性,且土壤中优势菌门放线菌门和变形菌门与Cd赋存形态和含量及土壤理化性质之间有应激响应。

To investigate the effects of Cd stress on the rhizosphere bacterial community in mulberry, mulberry variety Yuesang 1 was taken as the testing plant to conduct a pot experiment. Three cadmium(Cd) stressing concentrations(5, 3 and 2 mg/kg) simulating the severe, moderate and mild pollution levels, and the control(no Cd adding) were used in the pot experiment to analyze the bacterial diversity and community characteristics of rhizosphere soil. The results showed that under mild cadmium pollution stress, the bacterial ACE value, Chao1 index and Shannon index in mulberry rhizosphere soil were the highest, while the Simpson index was the lowest. Under severe cadmium pollution stress, the ACE value, Chao1 index and Shannon index were the lowest, while the Simpson index was the highest. Mulberry rhizosphere bacteria belonged to 21 phyla, of which the Acidobacteria and Proteobacteria were the two dominant phyla, accounting for 31.34%-62.60% and 19.64%-34.82% respectively. Omnitrophica and Elusimicrobia were peculiar bacteria occurring in the rhizosphere soil stressed by Cd. Redundancy analysis showed that there was a significant correlation between rhizosphere bacterial community structure and environmental factors. The dominant phylum of Proteobacteria was positively correlated with SOM, TN and TK, but negatively correlated with FMO-Cd, RES-Cd and EXC-Cd. The Acidobacteria phylum was positively correlated with TK, but negatively correlated with CAB-Cd and RES-Cd. The above results showed that the diversity of mulberry rhizosphere bacterial community could be enhanced under stress of low concentration of Cd, but be restrained under stress of high concentration of Cd. Meanwhile, the dominant phyla of Actinomycetes and Proteobacteria could response to the form and content of Cd, as well as the physical and chemical properties of the soil.