Effects of irrigation-induced salinity and sodicity on soil microbial activity

The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes β-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP.Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties.     

Enzymatic activities in constructed wetlands and di-n-butyl phthalate (DBP) biodegradation

The bioaccumulation of phthalate acid esters (PAEs) from industrial products and their mutagenic action has been suggested to be a potential threat to human health. The effects of the most frequently identified PAE, Di-n-butyl phthalate (DBP), and its biodegradation, were examined by comparison of two small scale plots (SSP) of integrated vertical-flow constructed wetlands. The influent DBP concentration was 9.84 mg l⁻¹ in the treatment plot and the control plot received no DBP. Soil enzymatic activities of dehydrogenase, catalase, protease, phosphatase, urease, cellulase, β-glucosidase, were measured in the two SSP after DBP application for 1 month and 2 months, and 1 month after the final application. Both treatment and control had significantly higher enzyme activity in the surface soil than in the subsurface soil (P<0.001) and greater enzyme activity in the down-flow chamber than in the up-flow chamber (P<0.05). In the constructed wetlands, DBP enhanced the activities of dehydrogenase, catalase, protease, phosphatase and inhibited the activities of urease, cellulase and β-glucosidase. However, urease, cellulase, β-glucosidase activities were restored 1 month following the final DBP addition. Degradation of DBP was greater in the surface soil and was reduced in sterile soil, indicating that this process may be mediated by aerobic microorgansims. DBP degradation fitted a first-order model, and the kinetic equation showed that the rate constant was 0.50 and 0.17 d⁻¹, the half-life was 1.39 and 4.02 d, and the r² was 0.99 and 0.98, in surface and subsurface soil, respectively. These results indicate that constructed wetlands are able to biodegrade organic PAEs such as DBP.     

Enzyme activity and microbial biomass in a field soil amended with municipal refuse

Summary Changes in enzyme activity levels, in biomass-C content, and in the rate of fluorescein diacetate hydrolysis were measured in a loamy soil to which solid municipal refuse had been applied as compost over a 3-year period at two different rates. Addition of the compost caused significant increases in the activity of all enzymes tested. The increases were much higher at 90 t ha^-1 year^-1 than at 30 t ha^-1 year^-1. Significant increases were also observed in the biomass-C content and in the rate of fluorescein diacetate hydrolysis. Significant correlations among changes in biomass-C content and the rate of fluorescein diacetate hydrolysis and the changes in all enzymes tested were found.Two activity indices were calculated; a biological index of fertility and an enzyme activity number. No correlations were found between the biological index of fertility and the changes in the various enzyme activities. However, significant correlations were found either between enzyme activity number and most of the changes in enzyme activity, or between the enzyme activity number index and the biomass-C content (r=0.850). The use of a new activity index, the hydrolysis coefficient, is proposed. This coefficient was significantly correlated with biomass-C content (r=0.925) and with the enzyme activity number index (r=0.780).     

Enzymatic activity as a parameter for the characterization of the composting process

Enzymatic activity (EA) was explored as a possible tool for composting characterization. Three composts (yard wastes, cotton wastes and a mixture of the two) were sampled during different phases of the process and divided in two fractions. The first was immediately analysed for microbial biomass C (B_C) and EAs (β-glucosidase, arylsulphatase, acid and alkaline phosphatase). The second fraction was air-dried prior to analysis for the same EAs and for organic C (C_ORG), total N (N_TOT), dissolved organic C (DOC), extractable C (C_E) and humic-like C (C_H).B_C decreased throughout the composting period (149 days), whereas EA in moist fractions stabilized between 50 (β-glucosidase, alkaline phosphatase) and 90 (arylsulphatase, acid phosphatase) days of composting.EA was always reduced by air‐drying (β-glucosidase: 40-80%; arylsulphatase: 10-50%; acid phosphatase: 10-70%; alkaline phosphatase: 50-90%), but this effect was less prominent as composting proceeded, especially for β-glucosidase and alkaline phosphatase.EA in air-dried samples displayed the same trend as in moist ones, except that there was a marked difference (47-66%) between initial and final activities of all four enzymes.EAs in air‐dried compost and content of humic-like substances showed a similar trend: a marked increase in the first 90 days of the process and no significant variations afterwards. This suggests that the formation of humic-enzymatic complexes has taken place and indicates that this process occurs almost totally during the first stage of composting.EA steadiness in air-dried samples occurred concurrently with the achievement of compost stability, as indicated by the conventional indexes (i.e. C_H, C_ORG/N_TOT). Therefore, the development of a stable enzyme activity in air-dried compost could represent a simple measure of compost stabilization in routine analysis of composting process.     

小麦茎秆木质素代谢及其与抗倒性的关系

以抗倒性不同的6个小麦品种为材料,观测了茎秆基部第二节间的木质素含量及苯丙氨酸转氨酶(PAL)、酪氨酸解氨酶(TAL)、肉桂醇脱氢酶(CAD)和4-香豆酸: CoA连接酶(4CL)活性以及不同时期茎秆抗折力和倒伏指数的变化,探讨木质素含量与抗倒伏能力的关系。不同小麦品种的茎秆木质素含量存在明显差异。茎秆抗折力大、倒伏指数小的品种(济麦20和济麦22),其茎秆木质素含量高,PAL、TAL、CAD和4CL活性强。相关分析表明,茎秆木质素含量与实际倒伏率呈显著负相关(r = -0.83, P<0.05);与抗折力呈显著正相关(r = 0.86, P<0.05);PAL、TAL和CAD活性与木质素含量呈显著正相关(r =0.78, 0.77, 0.85, P<0.05),4CL活性与木质素含量呈不显著正相关(r =0.39, P>0.05)。研究表明,较高的PAL和CAD活性是木质素含量高的酶学基础,茎秆木质素含量可作为小麦品种抗倒伏性评价的一个重要指标。     

酶法水相提取大豆油难点的解决方法

大豆含油量较低，酶法水相提油困难。为提高得率而加大酶用量，则成本高，无法应用。本研究以水浸提大豆含油蛋白，最适条件下96％大豆油随蛋白进入水提液，少量蛋白酶降解水液中的大豆蛋白，使部分大豆油释放，再离心分离，释放的部分大豆油被分离出的蛋白吸附，得到高作含油量的大豆蛋白则可按已有的适用于高含油量油料的水提法进行提油，解决了大豆油酶法水提的难点。     

微生物和酶学技术在烟草发酵中的应用及展望

综述了微生物和酶学技术在烟草发酵中的应用及其研究进展,重点阐述了陈化烟叶表面微生物区系与优势菌种的筛选、分离和鉴定;外源有益微生物协调与改善陈化烟叶化学组分,提高烟叶香气量,缩短烟叶陈化周期;以及添加外源生物活性酶降解烟叶中淀粉、蛋白质、纤维素等大分子物质等方面的研究现状,分析了目前该领域研究中存在的问题,认为将现代分子生物学技术与传统的方法相结合来深入研究烟叶发酵机理及其增香技术仍是今后研究的关键。     

岗平地黑土草田轮作的生态效应

以玉米连作为对照 ,研究了草田轮作对岗平地黑土的生态效应。结果表明 :在水蚀和风蚀严重的岗平地黑土上实行草田轮作 ,有利于改善土壤的孔隙状况 ,从而改善岗平地黑土的通气有余、持水不足、易于干旱和沙化的状况。草田轮作可以增加土壤微生物的数量 ,增强微生物的总体活性 ,也可以增加土壤的酶活性 ,进而提高土壤的生物活性 ,改善土壤的环境条件。     

不同浓度IAA对烤烟酶活性及钾和烟碱含量的影响

采用盆栽试验,研究了打顶后喷施不同浓度IAA对烤烟叶片中硝酸还原酶(NR)、转化酶(Inv)活性,根系活力及烟叶中钾和烟碱含量的影响.结果表明:打顶后喷施适宜浓度的IAA(20 mg/kg)可以增加烟叶NR活性,减缓烟叶Inv活性下降程度,有利于提高根系活力,增加烟叶钾含量,同时具有降低烟碱含量的作用.     

白灵菇产木聚糖酶营养条件的优化

以白灵菇为出发菌株,研究该菌株在不同碳源、氮源、无机盐的条件下产木聚糖酶活力大小,从中筛选出最佳培养基配方。通过测量菌丝干重,采用DNS法测定白灵菇产木聚糖酶活性大小,并根据碳源、氮源、无机盐对白灵菇产木聚糖酶的活性的影响,得出白灵菇最适培养基组成为:甘蔗渣5%、黄豆粉2%、MgSO40.15%、KH2PO40.3%、ZnSO40.01%、VB12粒。发酵液酶活力可达到60.50U/ml。