Modelling density thresholds for managing mouse damage to maturing wheat

Predator-prey theory suggests that pest damage that occurs over a period of time is related to the initial pest density and their functional and numerical responses to the resource. Estimating the relationship between damage and initial density is therefore fundamental to determining the threshold density (D_T), above which the economic benefits of control exceed the economic costs of control. A manipulative experiment was conducted to parameterize a model of D_T for managing yield loss (YL) caused by mice (Mus domesticus L.) from the milky stage to harvest, by assessing the relationship between YL and initial mouse density at the milky stage (D_I). This relationship subsumed the functional and numerical response of mice to maturing wheat crops. The experiment was conducted in a typical wheat field and D_I was manipulated by releasing a known number of mice into an experimental crop enclosed by a mouse proofed fence. The estimated relationship was asymptotic exponential: YL increased almost linearly with D_I until apparent competition between mice occurred at densities in excess of about 500 mice ha⁻¹; and apparent competition limited further increases in YL at densities in excess of 2133 mice ha⁻¹. D_T varied depending on the effectiveness of the control method in reducing D_I and the cost of control as a percentage of the farm-gate value of wheat. D_T was 89 mice ha⁻¹ for triggering aerial baiting if this method was effective in reducing D_I by 41% and if the cost of baiting was 7.54% of farm-gate value of wheat. Grain growers will be able to use D_I immediately to make informed, timely decisions for managing mouse damage to wheat crops. Mouse densities should be monitored well before the milky stage so that D_I can be forecast by the trend of monitored densities. If the forecast D_I exceeds D_T, management should be implemented at least a week before the milky stage (allowing a week for control such as baiting to take effect). However, if the forecast D_I is much higher than D_T so that even after control the reduced D_I would still be higher than D_T, then additional control may be applied so that the final control applied a week before the milky stage would reduce D_I below D_T.     

Identifying response groups of soil nitrifiers and denitrifiers to grazing and associated soil environmental drivers in Tibetan alpine meadows

Defining response groups within N-related microbial communities is needed to predict land management effect on soil N dynamics, but information on such response groups and associated environmental drivers is scarce. We investigated the abundance and major populations of ammonia-oxidizing archaea (AOA) and bacteria (AOB), and nirS- and nirK-harboring denitrifiers under different grazing managements in Tibetan alpine meadow soils. Grazing increased AOB and AOA abundances up to 42 fold and 3.7 fold, respectively, and increased the percentage of AOB within total ammonia oxidizers from 3.1% to 10.8%. The abundance of nirK-like denitrifiers increased with grazing intensity, while the abundance of nirS-like denitrifiers tended to decrease. However, sub-groups within each of these broad groups of (de)nitrifiers responded differently to grazing. Soil nitrate was the main driver of the abundance of denitrifier sub-groups (nirK or nirS) positively responding to grazing, while soil moisture and carbon concentration were the main drivers of the abundance of denitrifier sub-groups negatively responding to grazing. AOB and nirK-harboring denitrifiers thus generally responded more positively to grazing than AOA and nirS-harboring denitrifiers, but significant functional diversity existed within each group. Our approach demonstrates the usefulness of the concept of response groups to better characterize and understand (de)nitrifier response to grazing.     

反刍动物体内尿素循环及其转运蛋白的分子调控机制研究进展

虽然在哺乳动物体内都存在尿素循环利用机制,但是反刍动物由于瘤胃的存在而使得尿素循环在维系机体氮平衡和提高氮素利用效率等方面发挥着更加重要的生物学意义。通过瘤胃壁扩散或转运,血液中的尿素可进入胃肠道,在脲酶的作用下转化为氨态氮,从而为瘤胃微生物蛋白合成提供氮源。研究表明,尿素在瘤胃上皮的自由扩散速度较慢,而尿素转运蛋白可以介导尿素分子高效地进行跨膜转运,其也被认为是反刍动物尿素循环最重要的调控因子。然而,相关报道已经证实,尿素转运蛋白的表达和功能发挥受到日粮营养水平与结构组成、瘤胃内环境、动物年龄等因素的影响。本文以尿素循环为出发点,重点阐述了反刍动物体内尿素循环的特点、影响因素以及尿素转运蛋白的表达特征及其分子调控过程,以期从分子生物学角度解析反刍动物尿素循环的作用机制,从而为生产实践中动物氮素的精准营养提供理论依据和技术支撑。     

刈割后追肥对建植当年紫花苜蓿生长和生产性能的影响

施肥是苜蓿生产的重要管理措施之一,但苜蓿刈割后的追肥效应以及最佳追肥管理方案尚不明确。本研究旨在探讨追肥时间和不同氮、磷追施配比对苜蓿刈割后再生长的影响。以建植当年陇东苜蓿为试验材料,设置两个追肥时间（刈割当日和刈割后7 d,分别表示为T₀和T₁）、3个氮肥水平（0、25和50 kg·hm^-2 N,分别表示为N₀、N₂₅和N₅₀）和3个磷肥水平（0、30、60 kg·hm^-2 P₂O₅,分别表示为P₀、P₃₀和P₆₀）,并设3个重复,共54个小区。研究发现：1）建植当年苜蓿刈割后追肥促进了后茬苜蓿的生长,其中刈割后立即施用少量磷肥（T₀N₀P₃₀）处理下株高最高,比对照（T₀N₀P₀）增加了20.53%。刈割后追肥提高了苜蓿的叶茎比,在T₁时进行高氮低磷配施（N₅₀P₀和N₅₀P₃₀）中最为明显。2）第2茬苜蓿产量在不同处理间差异显著（P<0.05）,其中刈割后立即高磷高氮追施（T₀N₅₀P₆₀）下干物质和粗蛋白产量最高,分别为3.58和0.94 t·hm^-2,与T₁处理下的结果有显著差异。刈割后追肥对苜蓿酸性洗涤纤维、中性洗涤纤维含量和相对饲用价值均无显著影响（P>0.05）。3）氮磷肥配比追施对单位体积土壤中后茬苜蓿的根长、根表面积、根体积和根生物量影响显著（P<0.05）。最大根长密度（2.66 mm·cm^-3）和根表面积密度（7.75 mm²·cm^-3）出现在无肥（N₀P₀）、T₀N₂₅P₃₀处理中,根体积密度在T₁N₂₅P₃₀条件下最大。不同处理的根系生物量差异较大,但均高于不施肥处理（N₀P₀）。综上所述,在陇东黄土高原雨养农区,刈割后追施氮、磷肥促进了建植当年苜蓿的再生。在当地的生产实践中,建议在苜蓿刈割后立即追施少量磷肥（30 kg·hm^-2 P₂O₅）或每公顷配合追施50 kg N和60 kg P₂O₅。     

水氮梯度对饲用甜高粱生长和水分利用效率的影响

  【目的】  探究不同灌溉量和施氮水平对饲用甜高粱生长特性、单株耗水规律以及水分利用效率的影响,为确定饲用甜高粱适宜种植密度、优化水氮管理措施以及提高栽培生产潜力提供理论支撑。  【方法】  在温室条件下进行二因素三水平随机区组试验,供试饲用甜高粱品种为‘大力士’。设置了3个灌溉量,分别为达到田间持水量的30%～50% (I1)、50%～70% (I2)、70%～90% (I3);设置了3个施氮水平,分别为0 kg/hm2 (N0)、200 kg/hm2 (N1)、400 kg/hm2 (N2)。在饲用甜高粱拔节期取样,测定甜高粱株高、茎粗、鲜重与干重。同时,采用自动称重式蒸渗仪测定单株耗水动态,计算了干物质水分利用效率。  【结果】  1)增加灌溉量显著增加了饲用甜高粱株高和茎粗,与I1相比,I2、I3灌溉量下甜高粱株高分别提高了20.0%和34.5%,茎粗分别增加了18.0%和36.6%。施氮对株高和茎粗无显著影响。2)增加灌溉量显著提高甜高粱植株茎、叶及地上部鲜重和干重,施氮水平仅显著影响叶的鲜重和茎的干重。与I1相比,I2、I3灌溉量下地上部整株鲜重分别提高158.1%、290.1%,干重分别提高84.8%、139.3%。与N0相比,N1、N2施氮量下叶的鲜重分别提高7.6%、4.6%,茎的干重分别降低8.5%、10.4%。I1灌溉量下茎叶比<1,I2和I3灌溉量下茎叶比>1,随着灌溉量增加,饲用甜高粱茎叶比显著增加。在I1、I3灌溉量下,茎叶比随着施氮量的增加而降低。3)随着灌溉量的增加,甜高粱单株耗水量显著增加,而水分利用效率则显著下降。与I1相比,I2、I3灌溉量下累积耗水量分别提高了101.3%、178.9%,水分利用效率分别降低了8.0%、13.9%。施氮对甜高粱单株累积耗水量及水分利用效率均无显著影响。  【结论】  灌溉量显著影响着甜高粱的生长、干物质量的积累以及干物质向茎秆的分配,过高的灌水量会增加饲用甜高粱的耗水量,降低水分利用效率。氮素对甜高粱的生长未显现出促进作用,高施氮量还会增加干物质在叶片中的分配。因此,适度灌溉并施用少量氮肥可能更适合甜高粱的饲用品质和高水分利用效率。     

含水量和乳酸菌添加剂对多花黑麦草青贮品质的影响

本试验旨在研究含水量和乳酸菌添加剂对多花黑麦草青贮品质的影响,探究优质多花黑麦草青贮饲料的调制方法。试验选用孕穗期的多花黑麦草为原料,原料含水量设85.23%(W₁),74.70%(W₂)和65.70%(W₃)3个水平,乳酸菌添加浓度设置对照组0 cfu/g鲜样(L₀),10⁵ cfu/g鲜样(L₁),10⁶ cfu/g鲜样(L₂),10⁷ cfu/g鲜样(L₃)4个水平。桶装青贮42 d后开盖,取样测定青贮饲料的青贮品质。结果表明,在高含水量(85.23%)的条件下,无论是否添加乳酸菌,丁酸的含量和氨态氮/总氮均未能达到优质青贮的条件,青贮失败;当含水量为74.70%时,添加乳酸菌组的青贮品质优于未添加组,且随着添加浓度的增加青贮品质更佳;在含水量为65.70%的条件下,无论是否添加乳酸菌添加剂,青贮饲料均能获得较好的青贮品质,但添加乳酸菌后效果更佳。因此,W₃L₃(含水量65.70%+10⁷ cfu/g鲜样)处理的青贮效果最佳。     

多花黑麦草与水稻秸秆混合青贮品质的研究

以多花黑麦草（Lolium multiflorum）和水稻（Oryza sativa）秸秆为原料,按不同比例混合青贮,通过发酵品质和营养成分分析,筛选出适宜的混贮比例。结果表明：多花黑麦草单独青贮不易成功,与水稻秸秆以不同比例混合青贮均显著降低氨态氮/总氮的值以及乙酸、丙酸和丁酸的含量（P<0.05）,改善了发酵品质;其中7：3混贮处理发酵品质最佳,V-Score评分等级为优。从发酵品质以及秸秆利用最大化的角度出发,建议多花黑麦草与水稻秸秆以7：3混贮作为下一步研究的基础。     

基于转录组数据的印度谷螟微卫星位点分析

基于印度谷螟转录组测序数据筛选其功能微卫星(EST-SSR)分子标记,设计该虫的微卫星(SSR)引物并验证其适用性。用MicroSAtellite微卫星搜索软件查找印度谷螟转录组中微卫星的数量、重复次数以及所有微卫星的位置信息,采用Primer Premier 5软件设计SSR引物,并进行PCR验证。结果表明含EST-SSR的序列3 173个,占总搜索序列的8.52%,平均每13kb中就出现1个EST-SSR。共发现192种微卫星类型,其中重复单元为单碱基、二碱基和三碱基的比例较高,依次是28.21%、39.84%、25.43%。除单碱基重复单元外,出现频率最高的是AT/AT,有593次。在66对印度谷螟EST-SSR引物中,有28对PCR扩增成功。这说明基于印度谷螟转录组数据开发微卫星标记是可行的,本研究获得的印度谷螟EST-SSR位点为今后开展该虫的种群遗传学研究提供了基础数据。     

Specificity of antisera raised against synthetic peptide fragments of highMrglutenin subunits.

In an attempt to detect highM_rglutenin subunits specifically by immunochemical means, antisera were produced against synthetic peptides corresponding to three N-terminal sequences and to two repetitive motifs of highM_rglutenin subunits. The three N-terminal peptides, NT1, NT2 and NT3, differed by a single substitution at the sixth position and correspond, respectively, to the N-termini off Dx subunits, Ax and Bx subunits and By and Dy subunits. The anti-peptide sera did not cross react with gliadins or with lowM_rglutenin subunits, and differed in their ability to recognise highM_rglutenin subunits. The antisera to the repetitive motifs recognised all highM_rglutenin subunits, whereas the antisera to the N-terminal peptides detected only some of the subunits. The antiserum directed against the N-terminal peptide from Dx subunits detected these subunits specifically, whereas the antiserum directed against the N-terminal peptide corresponding to y type subunits did not react with the homologous subunits although it did react with Dx or Bx subunits. Antisera were also produced against internal sequences present in the N-terminal domain specific for x and for y-type subunits, but these antisera did not react with the cognate proteins. The failure of some anti-peptide sera to recognise the homologous highM_rglutenin subunits may be due to differences in conformation between peptides and the corresponding regions in proteins.     

Penialidins A–C with strong antibacterial activities from Penicillium sp., an endophytic fungus harboring leaves of Garcinia nobilis

Three new polyketides named penialidins A–C (1–3), along with one known compound, citromycetin (4), were isolated from an endophytic fungus, Penicillium sp., harbored in the leaves of the Cameroonian medicinal plant Garcinia nobilis. Their structures were elucidated by means of spectroscopic and spectrometric methods (NMR and HRMSⁿ). The antibacterial efficacies of the new compounds (1–3) were tested against the clinically-important risk group 2 (RG2) bacterial strains of Staphylococcus aureus and Escherichia coli. The ecologically imposing strains of E. coli (RG1), Bacillus subtilis and Acinetobacter sp. BD4 were also included in the assay. Compound 3 exhibited pronounced activity against the clinically-relevant S. aureus as well as against B. subtilis comparable to that of the reference standard (streptomycin). Compound 2 was also highly-active against S. aureus. By comparing the structures of the three new compounds (1–3), it was revealed that altering the substitutions at C-10 and C-2 can significantly increase the antibacterial activity of 1.