保水剂对土壤持水性能影响的模拟研究

通过室内模拟试验,利用正交回归设计研究了丙烯酸盐类保水剂对土壤持水性能的影响,并推导出土壤有效水含量与土壤质地、保水剂粒径及其使用剂量关系的数学模型。结果表明：土壤质地、保水剂用量对土壤有效水含量的影响达到极显著水平,而保水剂粒径对土壤有效水含量的影响不显著。保水剂颗粒与土壤质地、与保水剂用量成负效应,保水剂用量与土壤质地成正效应。这一数学模型可以用于指导该类保水剂在生产的使用。     

Identification and Characterization of Three Chitinases with Potential in Direct Conversion of Crystalline Chitin into N,N′-diacetylchitobiose

Chitooligosaccharides (COSs) have been widely used in agriculture, medicine, cosmetics, and foods, which are commonly prepared from chitin with chitinases. So far, while most COSs are prepared from colloidal chitin, chitinases used in preparing COSs directly from natural crystalline chitin are less reported. Here, we characterize three chitinases, which were identified from the marine bacterium Pseudoalteromonas flavipulchra DSM 14401^T, with an ability to degrade crystalline chitin into (GlcNAc)₂ (N,N’-diacetylchitobiose). Strain DSM 14401 can degrade the crystalline α-chitin in the medium to provide nutrients for growth. Genome and secretome analyses indicate that this strain secretes six chitinolytic enzymes, among which chitinases Chia4287, Chib0431, and Chib0434 have higher abundance than the others, suggesting their importance in crystalline α-chitin degradation. These three chitinases were heterologously expressed, purified, and characterized. They are all active on crystalline α-chitin, with temperature optima of 45–50 °C and pH optima of 7.0–7.5. They are all stable at 40 °C and in the pH range of 5.0–11.0. Moreover, they all have excellent salt tolerance, retaining more than 92% activity after incubation in 5 M NaCl for 10 h at 4 °C. When acting on crystalline α-chitin, the main products of the three chitinases are all (GlcNAc)₂, which suggests that chitinases Chia4287, Chib0431, and Chib0434 likely have potential in direct conversion of crystalline chitin into (GlcNAc)₂.     

基于DUS测试性状的上海鲜食玉米遗传多样性分析

基于DUS测试,对113个上海鲜食玉米品种进行田间种植试验,对采集的30个表型性状进行多样性分析、聚类分析和主成分分析,研究上海鲜食玉米的遗传多样性发展。结果表明,上海鲜食玉米的遗传变异积累相对单一,除了3个性状抽雄期与散粉期间隔天数(1.77)、抽雄期与抽丝期间隔天数(2.04)、植株的穗位高与株高比率(1.92)外,其他性状的多样性指数均处在0.18～1.50,有约26.67%的性状低于1.00。聚类分析表明,上海鲜食玉米的遗传背景存在趋同化现象,聚成5类时,前两类包含近61.06%的品种,类群Ⅲ和类群Ⅳ分别与其他类群有明显的差异,但是二者的品种量极少。主成分分析得出,生育期和雄穗等相关性状对上海地区鲜食玉米的评价有重要影响。     

河南省主要土类土壤耕层铅含量抽样调查

对河南省主要土类土壤耕层铅含量进行了抽样调查,60个随机抽样点的检测结果表明,潮土、褐土、砂姜黑土、黄褐土、黄棕壤铅含量高低不一,铅含量平均值大小顺序为:砂姜黑土>褐土>黄褐土>潮土>黄棕壤,但均未超过国家《土壤环境质量标准》(GB15618-1995)中的铅污染指标。     

Breeding for improved resistance to Edwardsiella ictaluri in striped catfish (Pangasianodon hypophthalmus): Quantitative genetic parameters

Bacillary necrosis of Pangasius (BNP), caused by Edwardsiella ictaluri, is one of the most devastating diseases in striped catfish farming. To date, quantitative genetic inheritance of BNP resistance is not known in striped catfish Pangasianodon hypophthalmus. The main aim of this study was to estimate genetic parameters for BNP resistance in a breeding population of striped catfish undergoing four generations of selection for high growth. Specifically, the study examined whether BNP resistance is heritable to enable family selection and whether genetic improvement for enhanced BNP resistance may have detrimental effects on growth and survival rate. To test these hypotheses, 720 full‐ and half‐sib families were challenged with E. ictaluri pathogen using injection and cohabitation methods over four years, from 2010 to 2012 and 2015. In total, the data included 398,234 animals in the pedigree, from which 18,849 animals had disease challenge test records and 39,103 siblings had growth performance. Both univariate and bivariate sire–dam linear and threshold mixed models were used to estimate (co)variance components for BNP resistance, survivals and growth traits. The estimates of heritability for the BNP resistance recorded as death or survival were low regardless of models used (0.10–0.16), whereas survival time (days post‐challenge test) showed moderate heritability (0.35). The survival rate during hapa rearing had medium heritability (0.33–0.52). The genetic correlations of BNP resistance with body weight and survival were all positive (0.03–0.53), suggesting that selection of increased BNP resistance may have positive impacts on growth and survival traits, and these traits could be easily improved simultaneously in the selective breeding programme for striped catfish.     

The use of machine learning to predict acute hepatopancreatic necrosis disease (AHPND) in shrimp farmed on the east coast of the Mekong Delta of Vietnam

Fisheries Science - Predicting the outbreak of disease is essential when managing shrimp farms. Acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus is a serious...     

麻栎人工林水源涵养效能研究

对麻栎人工林和原造林地灌丛、草地的水文要素进行了比较分析。结果表明：中龄麻栎人工林在生长季节,林冠层对一次降雨的拦截能力可达８．７ｍｍ,凋落物层的涵蓄能力可达３．１ｍｍ,分别是灌丛和草地的３倍和６倍;土壤对一次降雨的最大涵蓄量为９１０ｔ／ｈｍ２,分别比灌丛和草地高了５４％和７２％。可见营造麻栎林后,有效地提高了原有植被拦蓄降水的能力,减少地表径流发生的机会和数量,发挥了较好的水源涵养效能     

全乳固体快速测定方法研究

在ＧＢ５４０９－８５减重法的基础上,以滤纸代替海砂,略去水浴浓缩过程,烘箱内一步干燥至恒重,使测定时间从４～ｈ缩短至９０～１２０ｍｉｎ,与ＧＢ５４１８－８５减重法相比测定时间大大缩短,准确度无差异。     

锥虫抗药性机制的研究进展

为了较全面地了解锥虫抗药性机制的研究进展,综述了国内外有关报道。锥虫抗药性形成的机制主要表现在三方面,即锥虫体内酶的活性（或含量）发生变化,抗药株虫体的苹果酸酶、锥虫硫酮还原酶或鸟氨酸脱羧酶等酶的活性明显升高;锥虫细胞膜上的特异载体,即细胞膜上转运腺苷酸和腺苷的Ｐ２载体发生改变,药物进入虫体受阻;虫体的抗药基因被激活或基因发生重组、突变或扩增。本文还总结了锥虫抗药性机制研究中存在的问题及今后的研究