3种类型秸秆降解对黑土微生物群落及功能的影响

秸秆的降解主要依赖于微生物对木质纤维素残体的作用.黑土土质肥沃,富含微生物,利用宏基因组测序了解秸秆降解过程中黑土微生物的变化具有重要意义.以3种东北黑土区典型农作物秸秆即大豆、水稻、玉米秸秆为材料,加入到黑土中,在30℃条件下进行微宇宙实验,分析在秸秆降解过程中土壤微生物群落和功能的变化.结果表明,大豆、水稻和玉米秸秆在黑土环境中富集了不同的微生物.大豆秸秆主要富集放线菌(Actinobacteria)、绿弯菌(Chloroflexi)、COG1858,水稻秸秆主要富集拟杆菌(Bacteroidetes)、疣微菌门(Verrucomicrobia)、COG1472、COG3250,玉米秸秆主要富集变形菌(Proteobacteria)、酸杆菌(Acidobacteria)、ENOG410XNTA.不同类型的秸秆降解过程中会富集不同的木质纤维素降解菌,木质纤维素降解相关的功能途径和酶的丰度也有所增加.

Microbial extraction of nickel from chromite overburdens in the presence of surfactant

The effect of surfactant polyoxyethylenesorbitan monolaurate （Tween-20） on the nickel bioleaching from pre-treated chromite overburden （COB）, Sukinda with fungal strain Aspergillus niger, was examined in shake flasks. Along with the nickel recovery from COB by the fungal bioleaching, the effect of surfactant on the growth of the A. niger was also investigated. Results show that the addition of surfactant in low concentration was favorable for the recovery of nickel from pre-treated COB. Normally, the carbon source （sucrose） in the culture medium was utilized by the A. niger for its cellular metabolism and organic metabolites （bio acids） were produced, which were responsible for the bioleaching of minerals. However, the addition of surfactant （Tween-20） accelerated the rate of sucrose consumption by the fungi, and thus enhancing the extraction of nickel from pre-treated COB. During the study, around 39% nickel extraction was achieved in A. niger mediated bioleaching performed at 2% pulp density of pre-treated COB at 30 °C, in the presence of surfactant whereas only 24% nickel was extracted without surfactant.

Effects of Earthworms and Ryegrass on the Removal of Fluoranthene from Soil

Earthworms can promote the bioremediation of contaminated soils through enhancing plant growth and microorganism development. The individual and combined effects of earthworms and ryegrass （Lolium multifloram Lain.） on the removM of fiuoranthene from a sandy-loam alluvial soil were investigated in a 70-d microcosm experiment. The experiment was set up in a complete factorial design with treatments in four replicates： without earthworms or ryegrass （control, CK）, with earthworms only （E）, with ryegrass only （P）, and with both earthworms and ryegrass （EP）. The residual fluoranthene, microbial biomass C, and polyphenol oxidase activity in the soil changed significantly （P 〈 0.01） with time. In general, the residual concentration of fluoranthene in the soil decreased sharply from 71.8-88.7 to 31.7-37.4 mg kg-1 in 14 d, and then decreased gradually to 19.7-30.5 mg kg-1 on the 70th d. The flu- oranthene concentration left in the soil was the least with both earthworms and ryegrass, compared to the other treatments at the end of the experiment. Half-life times of fluoranthene in the E, P, and EP treatments were 17.8%-36.3% smaller than that of CK. More fluoranthene was absorbed by earthworms than ryegrass. However, the total amounts of fluoranthene accumulated in both the ryegrass and earthworms were small, only accounting for 0.01%-1.20% of the lost fluoranthene. Therefore, we assumed that microbial degradation would play a dominant functional role in fluoranthene removal from soil. We found that earthworms significantly increased microbial biomass C and polyphenol oxidase activity （P 〈 0.01） in the presence of ryegrass at the end of the experiment. Furthermore, microbial biomass C and polyphenol oxidase activity were significantly （P 〈 0.05） and negatively related to the residual fluoranthene concentration. This implied that earthworms might promote the removal of fluoranthene from soil via stimulating microbial biomass C and polyphenol oxidase activity.

Fertilization regimes affect the soil biological characteristics of a sudangrass and ryegrass rotation system

The sudangrass (Sorghum sudanense) and ryegrass (Lolium multiflorum L.) rotation is an intensive and new cropping system in Central China.Nutrient management practices in this rotation system may influence soil fertility,the important aspects of which are soil biological properties and quality.As sensitive soil biological properties and quality indicators,soil microbial community activity,microbial biomass,enzyme activities,soil organic matter (SOM) and total N resulting from different fertilization regimes in this rotation system were studied through a four-year field experiment from April 2005 to May 2009.Treatments included control (CK),fertilizer phosphorus and potassium (PK),fertilizer nitrogen and potassium (NK),fertilizer nitrogen and phosphorus (NP) and a fertilizer nitrogen,phosphorus and potassium combination (NPK).Soil microbial community activities in the NK,NP and NPK treatments were significantly lower than those in the CK and PK treatments after the sudangrass and ryegrass trial.The highest microbial biomass C,microbial biomass N,SOM,total N,sucrase and urease activities were found in the NPK treatment,and these soil quality indicators were significantly higher in the NK,NP and NPK treatments than in the PK and CK treatments.Soil microbial biomass and enzyme activities were positively associated with SOM in the sudangrass and ryegrass rotation system,indicating that fertilization regimes,especially N application,reduced microbial community activity in the soil.Proper fertilization regimes will increase microbial biomass,enzyme activity and SOM and improve soil fertility.