[Effects of straw-returning combined with application of microbial inoculants on soil aggregates and related nutrients]. / ç§¸ç§†è¿˜ç”°é æ–½ä¿ƒè èŒå‰‚å¯¹åœŸå£¤å›¢èšä½“åŠå ¶å »åˆ†çš„å½±å“.

We analyzed the particle size distribution of soil aggregates in 0-20 and 20-40 cm soil layers of rice-wheat rotation field based on a field plot test with two treatments, conventional straw returning (CK) and straw returning with the addition of straw decomposition promoting microbial inoculants (IT). We evaluated the water stability indices of soil aggregates (the number of soil water stable large aggregates R0.25, the average weight diameter MWD, and the geometric average diameter GMD), and measured the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the soil aggregates of ＜0.053, 0.053-0.25, 0.25-1, ＞1 mm. The results showed that: 1) The number of aggregates ＜0.053, 0.053-0.25, ＞0.25 mm in the 0-20 and 20-40 cm soil layers under IT decreased by 10.0% and 6.8%, increased by 3.0% and 5.7%, and 17.9% and 26.1% compared with CK, respectively. IT effectively increased R0.25, MWD, and GMD by 26.4%, 20.0%, 18.2% and 18.2%, 10.5%, 10.0% in 0-20 and 20-40 cm soil, respectively. 2) Compared to CK, the TP content of 0.25-1 mm aggregates in 0-20 and 20-40 cm soil under IT was significantly increased by 40.3% and 37.5%, respectively, without difference in TN and SOC contents. There was no significant difference in nutrient contents of the other aggregates between the treatments. The contents of SOC and TN in large aggregates (>0.25 mm) were higher than those in silty aggregates (<0.053 mm). Compared to CK, the cumulative contribution rates of SOC, TN and TP of <0.053 mm aggregates under IT were decreased in two soil layers. There was no significant difference in the nutrient cumulative contribution rates of 0.053-0.25 mm aggregates between treatments. The cumulative contribution rates of SOC, TN, and TP of large aggregates (>0.25 mm) under IT were 32.1%, 19.6%, 52.8% and 22.8%, 11.8%, 42.9% higher than those under CK in 0-20 and 20-40 cm soils, respectively. 3) The number of <0.053 mm aggregates was significantly negatively correlated with SOC and TP contents, while that of 0.053-0.25 mm aggregates was negatively correlated with nutrient content. The number of large aggregates (>0.25 mm) were significantly positively correlated with SOC, TN, and TP contents. In conclusion, straw returning with microbial-inoculant addition could promote the formation of soil macroaggregates (>0.25 mm), and improve the water stability of soil aggregates, increasing nutrient contents in soil macroaggregates, with the nutrients transferring from silty aggregates to macroaggregates.

Genomic and physiological characterization of an antimony and arsenite-oxidizing bacterium Roseomonas rhizosphaerae.

Antimony (Sb) and arsenic (As) are two toxic metalloids, which are listed as priority environmental pollutants by the European Union and the U.S. Environmental Protection Agency (EPA). Antimony taken up by plants enters the food chain and poses a threat to human health. Microbial oxidation of antimonite (Sb(III)) and arsenite (As(III)) to the less toxic antimonate (Sb(V)) and arsenate (As(V)), has great potential for the immobilization of Sb and As in the environment. A heterotrophic aerobic bacterium, Roseomonas rhizosphaerae YW11, oxidized both Sb(III) and As(III) in the modified R2A medium. In the same medium, strain YW11 preferred to oxidize Sb(III), whereas the As(III) oxidation rate was only 50%. Genomic analysis of YW11 confirmed the presence of several As-resistance gene islands. The aioAB genes encoding As(III) oxidase were also induced by Sb(III). The role of aioA in Sb(III) oxidation and resistance was confirmed by disrupting this gene in strain YW11, resulting in the loss of Sb(III) oxidation abilities. This study documents an enzymatic basis for microbial Sb(III) oxidation in strain YW11, which is a novel bacterial strain showing simultaneous oxidation of Sb(III) and As(III), and may be a potential candidate for bioremediation of heavy metal-contaminated environments.