Growth,Cadmium Accumulation Characteristics,and Soil Microecological Response Of Various Cadmium Tolerant Millet Varieties

Cadmium（Cd）is a heavy metal element with strong biological toxicity,which belongs to a non-essential element for plants.With the rapid development of industry and agriculture,Cd pollution has become more and more serious.It can be absorbed by plants through water,soil and other ways,and enter the human body through the food chain,thus causing harm to the human body.Therefore,the safe utilization and remediation of Cd contaminated soil has become a hot issue.In this study,58 millet varieties widely used in the main cultivation areas of millet were selected as the tested materials.By studying its germination characteristics under 100 mg.L^-1Cd stress,the tolerance difference of different millet varieties to Cd stress was identified,and the Cd-resistant millet database was constructed;according to the evaluation results of Cd tolerance and adaptability,six Cd tolerant varieties were selected;through pot experiment,the absorption and transportation characteristics of different varieties to Cd were studied,and six Cd tolerant varieties were divided into high and low Cd accumulation types according to the Cd content of various organs among varieties.The growth characteristics,plant physiological characteristics,soil microbial community diversity and soil enzyme activity of different Cd accumulation millet varieties were studied,so as to clarify the response differences of growth of different Cd accumulation millet varieties and their soil micro-ecosystem to Cd.It provides the theoretical basis and technical support for the safe and effective utilization of cadmium-contaminated soil under the condition of moderate and light cadmium pollution.The main results are as follows:（1）The results of cluster analysis showed that the percentage of Cd tolerant varieties was 20.69%,the relative germination rate and the relative germination potential were≥60.00%;the percentage of Cd tolerant varieties was 22.41%,the relative germination rate was40.00%-65.00%,the relative germination potential was 30.00%-45.00%;the percentage of Cd intolerant varieties was 56.90%,the relative germination rate was less than 40.00%,and the relative germination potential was less than 38.00%.The comprehensive evaluation of cadmium tolerance of millet varieties was carried out by using the membership function of mold and mathematics,and the results showed that the comprehensive scores of varieties were more than 5.（2）The content of Cd in different organs of foxtail millet was analyzed by cluster analysis,the varieties were divided into low and high Cd accumulation varieties.Among the low and high Cd accumulation varieties,the high Cd accumulation type was better than the low Cd accumulation type in Cd accumulation and transport capacity.Among them,Liaogu 2,the high Cd accumulation variety,had the strongest Cd accumulation and transport capacity,and the enrichment coefficients of root,stem,leaf and spike in Liaogu 2 were 0.54,0.65,0.53and 0.51,respectively;the transport coefficients of its stem,leaf and spike were 1.20,0.80and 0.98,respectively.（3）The growth conditions of low and high Cd accumulation varieties was different.The biomass of low Cd accumulation varieties was higher than that of high Cd accumulation varieties;The activities of antioxidant enzymes（SOD,POD,CAT）were higher in the low Cd accumulation varieties than in the high Cd accumulation varieties.The total chlorophyll content and soluble protein content of low Cd accumulation varieties were 1.62-1.87 times,1.09-1.88 times,1.07-1.24 times and 1.09-1.38 times of high Cd accumulation varieties during seedling stage and harvesting stage,respectively.（4）The activities of soil enzymes（urease,catalase,phosphatase）were higher in the low Cd accumulation varieties than in the high Cd accumulation varieties.The main Bacteriophyta of low and high Cd accumulation varieties was Proteobacteria,accounting for more than28.00%.Ascomycota was the main Eumycota in low and high Cd accumulation varieties,accounting for more than 59.00%.In addition,α-diversity and PCA analysis showed that the diversity of soil bacterial and fungal communities of varieties cultivated with low Cd accumulation（Niaobutan,Shijilvgu）was significantly different from that of varieties cultivated with high Cd accumulation（Liaogu 2,Liaofenggu 3）,suggesting that the soil microbial composition of different Cd resistant varieties was different.