Resistance mechanisms of cereal plants and rhizosphere soil microbial communities to chromium stress

Abstract

Abstract [Purpose]Agricultural soils contaminated with heavy metals poison crops and disturb the normal functioning of rhizosphere microbial communities. Different crops and rhizosphere microbial communities exhibit different heavy metal resistance mechanisms. Here, indoor pot studies were used to assess the mechanisms of grain and soil rhizosphere microbial communities on chromium (Cr) stress. [Methods]Grain and soil samples were collected prior to (CK), 6 h after (Cr_6h), and 6 days following (Cr_6d) Cr stress. Transcriptomic analysis, high-throughput sequencing and quantitative polymerase chain reaction (qPCR) were used for sample determination and data analysis. [Results]Cr stress inhibited the expression of genes related to cell division, and photosynthesis in grain plants while stimulating the expression of genes related to DNA replication and repair, in addition to plant defense systems resist Cr stress. Cr stress also significantly influenced the composition and diversity of soil microbial communities. Bacterial community networks were larger than fungal community networks and were more tightly connected and less modular than fungal networks. However, both co-occurrence networks primarily comprised positively correlated edges that could serve to increase community stability. Only the abundances of AOA- and AOB-amoA genes significantly increased in relation to Cr stress (p < 0.05), while the abundances of other genes exhibited increasing trends with increased Cr exposure. [Conclusions]Overall, these results suggest that Cr stress primarily prevented cereal seedlings from completing photosynthesis, cell division, and proliferation while simultaneously triggering plant defense mechanisms to resist the toxic effects of Cr. Soil bacterial and fungal populations exhibited diverse response traits, community-assembly mechanisms, and increased expression of functional genes related to carbon and nitrogen cycling, all of which are likely related to microbial survival during Cr stress. This study provides new insights into resistance mechanisms, microbial community structures, and mechanisms of functional responses in cereal plants to heavy metal contaminated agricultural soils.