Effect Of Salinity-induced Organic Acid Metabolism On Cd Accumulation In Edible Amaranth Cultivars

The research object of this experiment was three Cd accumulation amaranth cultivars(low accumulate cultivars, Baiguxiaoyuanye; general accumulate cultivars, Quanhong; high accumulate cultivars, Liuye), which were previously screened by our own research group. Pot experiment was conducted with saline soils that were contaminated by Cd. The contents of Cd in shoots, roots and rhizosphere soil solution of amaranth were determined by atomic absorption spectrophotometer, and the content of organic acids were determined by Ion Chromatography; the microbial 16 S rDNA of rhizosphere soil was sequenced by high throughput sequencing method. In this research, the effect of organic acids metabolism and soil rhizosphere community structure of amaranth varieties on Cd accumulation in different amaranth cultivars was investigated. The main results were as follows:(1)Lactic acid, acetic acid, formic acid, malic acid, tartaric acid, and oxalic acid were detected in the shoots and roots of amaranth. Under salt stress conditions, amaranth mainly accumulated oxalic acid. Lactic acid, acetic acid, formic acid, malic acid, and oxalic acid were detected in all rhizosphere soil solution of amaranth. Under control and salt stress conditions, malic acid was not detected in rhizosphere soil solution of Baiguxiaoyuanye; malic acid was not detected in rhizosphere soil solution of Quanhong in the blank control, while the content of malic acid is 0.39 mg/kg under salt stress conditions. Compared with results in the control, the content of malic acid in rhizosphere soil solution of Liuye was increased from 0.10 mg/kg to 0.38 mg/kg. Under salinity induced conditions, the concentration of oxalic acid in rhizosphere soil solution varied among different amaranth cultivars species. The concentration of oxalic acid decreased mg/kg in the blank control from 0.07 to 0.02 mg/kg under salinity induced conditions for Baiguxiaoyuanye; the concentration of oxalic acid increased from 0.08 mg/kg in the blank control to 0.10 mg/kg under salinity conditions for Quanhong, and increased from 0.05mg/kg to 0.21mg/kg for Liuye.(2) Salinity promoted the heavy metals accumulation and transportation in amaranth cultivars. Baiguxiaoyuanye showed the least impact of salinity to Cd accumulation, while Baiguxiaoyuanye had the lowest capacity of Cd accumulation. The content of Cd in the roots of Liuye was 2.06 and 1.77 times of that in Baiguxiaoyuanye and Quanhong, respectively, while the content of Cd in the shoots was 10.02 and 3.26 times of that in Baiguxiaoyuanye and Quanhong. The contents of malic and oxalic acid are significantly positively correlated with the content of Cd in the rhizosphere soil solution of Liuye and Quanhong. The content of oxalic acid in the rhizosphere soil solution of Liuye was higher than that of Quanhong and Baiguixaoyuanye, which may be a vital factor that contributes to higher Cd accumulation in Liuye. Under salt stress conditions, there is not any malic acid detected and less oxalic acid in rhizosphere soil solution of Baiguxiaoyuanye, which may be the reason responsible for its low Cd accumulation characteristics.(3)The diversity of rhizosphere microbial in three different amaranth cultivars was investigated, and similar community structure of rhizosphere microorganisms was discovered. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the dominant communities in rhizosphere soils of amaranth. Under salt stress conditions, the salt tolerance of bacteria was increased in rhizosphere soil, and the Alpha microbial diversity of microbial in rhizosphere soils of three cultivars had little differences in the abundance of species. The Beta diversity of microbial had a great difference between the treatment and the control; under salt stress conditions, the microbial species composition in rhizosphere soils of three amaranth cultivars is similar, but quite different from that in the control.The results suggested that malic acid and oxalic acid which were secreted from the root of Amaranth cultivars activated the soil Cd. The contents of oxalic acid and malic acid in rhizosphere soil solution of different Amaranth cultivars were different, which was the mean reason for the difference of Cd accumulation in different Amaranth cultivars. The result laid the date foundation for studying the internal mechanism of different varieties of amaranths in saline soil that polluted by Cd and It also provides theoretical support for the safe cultivation of agricultural products.