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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...

Metacommunity theory provides an understanding of how ecological processes regulate local community assemblies. However, few field studies have evaluated the underlying mechanisms of a metacommunity on a small scale through revealing the relative roles of spatial and environmental filtering in structuring local community composition. Based on a spatially explicit sampling design in 2012 and 2013, this study aims to evaluate the underlying processes of a soil mite metacommunity on a small spatial scale (50 m) in a temperate deciduous forest located at the Maoershan Ecosystem Research Station, Northeast China. Moran’s eigenvector maps (MEMs) were used to model independent spatial variables. The relative importance of spatial (including trend variables, i.e., geographical coordinates, and broad- and fine-scale spatial variables) and environmental factors in driving the soil mite metacommunity was determined by variation partitioning. Mantel and partial Mantel tests and a redundancy analysis (RDA) were also used to identify the relative contributions of spatial and environmental variables. The results of variation partitioning suggested that the relatively large and significant variance was a result of spatial variables (including broad- and fine-scale spatial variables and trend), indicating the importance of dispersal limitation and autocorrelation processes. The significant contribution of environmental variables was detected in 2012 based on a partial Mantel test, and soil moisture and soil organic matter were especially important for the soil mite metacommunity composition in both years. The study suggested that the soil mite metacommunity was primarily regulated by dispersal limitation due to broad-scale and neutral biotic processes at a fine-scale and that environmental filtering might be of subordinate importance. In conclusion, a combination of metacommunity perspectives between neutral and species sorting theories was suggested to be important in the observed structure of the soil mite metacommunity at the studied small scale.

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.