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Pot experiments were carried out to study the effects of rice straw (RS) and rice straw ash (RSA) on the growth of early rice and α-diversity of bacterial community in soils around rare earth mining areas of Xunwu and Xinfeng counties in South Jiangxi of China. The results showed that the exploitation of rare earth resources leads to soil pollution around rare earth mining areas and affects the growth of rice, and the content of rare earth elements (REEs) in rice was positively correlated with that in soils and negative correlated with dry weight of rice; The addition of RS to soils around REE mining area can inhibit growth of early rice, and the dry weight of rice grains, shoots, roots is lower when compared with the controls, while the content of REEs is higher. The α-diversity of soil bacterial decreases, which promotes the growth of Pseudorhodoferax, Phenylobacterium and other bacteria of the same kind, and inhibits the growth of beneficial bacteria. The addition of RSA to soils had no significant effect on α-diversity of soil bacterial but promoted the growth of Azospira and other beneficial bacteria, inhibited the growth of Bryobacter and other bacteria of the same kind, significantly improved the dry weight of grains, shoots and roots of early rice, and reduced the content of REEs in these parts of rice. It can be concluded that RS is unsuitable to be added to the planting soil of early rice in REE mining area, while RSA is suitable. Rare earth elements (REEs) widely exist in the lithosphere, biosphere, hydrosphere and even the atmosphere, they migrate and transform in different geochemical environments through ways of precipitation and dissolution, adsorption and desorption, oxidation and reduction, complexation and biological enrichment, thus form different characteristics and patterns of distribution 1-5. The most important REE minerals are bastnasite, monazite, xenotime, ion-adsorbed rare earth ore and fergusonite. China owns 50% of REE resources and 90% of the ion-type REEs of the whole world, and provides 90% of REE products for the whole world. It is a major country for REE resources, production, export and consumption in the world 6,7. But the large-scale exploitation and extensive use of REE minerals have led to significant increase of REEs in the environment of mining area and its surroundings, which endangered food security and the health of local residents 8. Some studies have shown that the accumulation of REEs in the soil is obvious in downwind direction ranges from 8 km to 10 km below the tailings dam of Baotou Iron and Steel Company of China. The content of the mixed REEs in polluted soils near the tailings dam is 27549.58 mg•kg −1 , 118 times of the CK(control check) and 160 times of the average content of REEs in soils of China 9,10. It was found that the average content of REEs in the blood and hair of residents in Changting REEs mining area of Fujian province was higher than that of average people, and the exceeded content was 155.6 and 9.6 times of the standard respectively 11,12. In r...

The effects of rare earth mining on rice biomass, rare earth element (REE) content and bacterial community structure was studied through pot experiment. The research shows that the REE content in rice roots, shoots and grains was significantly positive correlated with that in soil, and the dry weight of rice roots, shoots and grains was highly correlated with soil physical and chemical properties, nutrient elements and REE contents; The exploitation of rare earth minerals inhibited a-diversity of endophytic bacteria in rhizosphere, root, phyllosphere and leaf of rice, significantly reduced the abundance index, OTU number, Chao, Ace index and also significantly reduced the diversity index–Shannon index, and also reduced uniformity index: Pielou’s evenness index, which caused β-diversity of bacteria to be quite different. The exploitation of rare earth minerals reduces the diversity of bacteria, but forms dominant bacteria, such as Burkholderia, Bacillus, Buttiauxella, Acinetobacter, Bradyrhizobium, Candida koribacter, which can degrade the pollutants formed by exploitation of rare earth minerals, alleviate the compound pollution of rare earth and ammonia nitrogen, and also has the function of fixing nitrogen and resisting rare earth stress; The content of soil available phosphorus in no-mining area is lower, and the dominant bacteria of Pantoea formed in such soil, which has the function of improving soil phosphorus availability. Rare earth elements and physical and chemical properties of soil affect the community structure of bacteria in rhizosphere and phyllosphere of rice, promote the parallel movement of some bacteria in rhizosphere, root, phyllosphere and leaf of rice, promote the construction of community structure of bacteria in rhizosphere and phyllosphere of rice, give full play to the growth promoting function of Endophytes, and promote the growth of rice. The results showed that the exploitation of rare earth minerals has formed the dominant endophytic bacteria of rice and ensured the yield of rice in the mining area, however, the mining of mineral resources causes the compound pollution of rare earth and ammonia nitrogen, which makes REE content of rice in mining area significantly higher than that in non-mining area, and the excessive rare earth element may enter the human body through the food chain and affect human health, so the food security in the REE mining area deserves more attention.

Pot experiments were conducted to explore the effects of different rice straw returning soil on the community structure and function of bacteria in rice root, rhizosphere, leaf and phyllosphere under 7 conditions of rice straw combined with different fertilizers respectively. The results showed that: rice straw returning in different ways increased the content of soil pH and K, and reduced the accumulation of N, P and organic matter in soil, and different rice straw returning ways had different effects; rice straw returning reduced dry weight of rice grain, 2% of rice straw returning reduced rice grain greater than that of 1% rice straw returning; The reduction of NP combined fertilization is greater than that of NK combined fertilization and NPK combined fertilization. Except for the decrease of chao_1 index in rice root at maturity, rice straw returning significantly improved the abundance, diversity and evenness of bacteria in rice root, rhizosphere, leaf and phyllosphere. Rice straw returning increased the content of REEs in rice, and 2% of rice straw returning soil increased rare earth element (REE) content in rice grain greater than that of 1% rice straw returning soil. Different ways of rice straw returning soil reduced the abundance of Bacillus, while the abundance of Exiguobacterium in rice leaves was hundreds of times higher than that of the control group, and the genus in leaves was dozens of times higher than that of the control group, 2% of rice straw returning soil increased the abundance of harmful bacteria and pathogens of Acidovorax, Clostridium sensu stricto, Citrobacter, Curtobacterium, and 1% of rice straw returning soil promoted the abundance of nitrogen fixing bacteria, plant growth-promoting bacteria, stress resistant bacteria such as Lactobacillus, Azospira, Acinetobacter, Bradyrhizobium and Acidocella; Environmental factors such as available P, organic matter, total nitrogen, nitrate nitrogen, rare earth element content in rice roots, available K and soil moisture are important factors affecting the community structure of bacteria in rice roots, rhizosphere, leaf and phyllosphere at tillering stage of the rice. pH, REE content in rice roots, shoots, organic matter, total nitrogen, nitrate nitrogen and soil moisture content are the main environmental factors affecting the community structure of bacteria in rice roots, rhizosphere, leaf and phyllosphere at maturity stage of rice. 2% rice straw returning soil promoted the formation of harmful bacteria, which may be an important reason for its significant reduction in the dry weight of rice grains.

Experiments were conducted in pots to study the effects of 2.5% rice straw and 1% rice straw ash on rice growth and bacterial community abundance in areas mined for heavy rare earth elements. The results showed that the incorporation of rice straw improved the pH value of soil, reduced the α-diversity of the soil bacterial community, improved the abundance of Proteobacteria and Firmicutes; reduced the abundance of Acidobacteria, Nitrospirae, etc.; reduced the abundance of Candidatus Solibacter, Syntrophobacter, Haliangium, Candidatus Koribacter; and increased the abundance of Ideonella, Anaeromyxobacter, Roseomonas, Clostridium sensu stricto 10, and Geobacter. The decrease in the abundance of beneficial bacteria, Acidobacteria and Nitrospirae, inhibited the growth of the rice; reduced the dry weight of the rice roots, the shoots, and the grains, and increased the concentration of rare earth elements in the rice. Returning 1% rice straw ash to the field had little effect on the diversity and richness of the bacterial community in areas mined for heavy rare earth elements. Also the returned rice straw had little effect on the rice growth, the dry weight of the roots, the shoots, the grains, and the concentration of rare earth elements in these parts of the rice.