亚热带丘陵茶园间作白三叶的土壤环境调控效果

在亚热带丘陵区1年生幼龄茶园通过连续4年间作白三叶大田试验,研究了其对茶园土壤环境及茶叶品质、产量的影响,结果表明,茶园间作白三叶降低了土壤容重,提高了土壤孔隙度、有机质、全氮、水解氮的含量及钾的活性,消耗了部分有效磷;增加了土壤关键层次（0～20cm）和关键时期（4～6月）的水分含量,延缓和缩短了夏季高温干旱与秋季持续干旱时间;获得了土壤降温时增温、保温与升温时降温的双向动态调控效果．增加了同一层次土壤温度的稳定性,延缓了高温和低温的出现时间,缩短了过度高温时间。从而促进了茶树生长,改善了茶叶品质,显著增加了茶叶产量。与清耕茶园相比,茶园间作白三叶后,春秋茶的酚氨比分别下降了17．10％和30．90％,产量提高了32.65％。     

覆盖与间作对亚热带丘陵茶园地温时空变化的影响

研究了亚热带丘陵茶园连续4年进行稻草覆盖与白三叶草间作对茶园地温时空动态变化的影响.结果表明,茶园地温具有明显的时空动态变化特征和位相滞后现象,与茶树的年生长发育周期各阶段的最适温度非常吻合.稻草覆盖与白三叶草间作改变了土壤热量交换层（地表层）的性质,具有升温时降温和降温时增温、保温的双向动态调控作用,降低了日较差,增强了同一土层温度的稳定性,其调控效果为随着土壤深度增加而降低,13：00>19：00>7：00,降温大于增温和保温,降温幅度随气温的升高而增大,增温和保温随气温的下降而加强,间作白三叶草的降温效果大于稻草覆盖,保温效果则相反.茶园地温时空变化转换点得到调节,显著地降低了有害高温的出现次数,明显地降低了持续高温期的土壤温度,有效地缩短了极限高温时间.     

地表覆盖对茶园土壤水分、养分变化及茶树生长的影响

以山东青岛2年生茶园为对象,设置对照(CK)、覆盖秸秆(T1)、覆盖地膜(T2)和覆盖秸秆+地膜( T3 )4个处理,分析了不同覆盖模式对茶园土壤水分和养分以及茶树生长的影响.结果表明:地表覆盖可以保持茶园土壤水分,提高水分利用效率,其中T1、T3处理的茶树生长水分利用效率比CK提高43％ ～48％,产量水分利用效率提高7％ ～ 13％;T1和T3处理土壤有机质、碱解氮、硝态氮、铵态氮的含量显著增加,提高了土壤肥力;叶片硝酸还原酶活性增强,叶片中硝态氮的含量增加,有效地促进茶树生长,茶叶产量比CK增加12％～13％,使茶树新梢生长高峰提前.从茶树生长、茶叶产量、水分和养分利用率、环境安全和经济效益等因素考虑,覆盖秸秆是幼龄茶园地表覆盖的有效方式.     

高温干旱季节遮阳网覆盖对茶园温湿度和茶树生理的影响

研究了高温干旱季节采用遮阳网覆盖红壤丘陵茶园的生态作用和对茶树生理的影响。与露地对照茶园相比,遮阳网覆盖处理茶园在高温干旱季节,各个观测时段的气温、树冠温度、叶面温度、地面温度和土壤温度均明显降低,茶园土壤水分含量、空气湿度和茶叶含水量明显提高,茶叶新梢的叶绿素、咖啡碱和氨基酸含量大幅度提高,茶多酚含量降低11．6％。连续高温干旱27～29d后遮阳网覆盖下茶树的叶片气孔导度、蒸腾速率和净光合速率均明显高于露地对照茶园。     

稻草覆盖、间作三叶草茶园土壤酶活性与养分的关系

通过小区实验,分析了稻草覆盖与间作三叶草后的丘陵茶园土壤过氧化氢酶、脲酶、蔗糖酶、磷酸酶活性变化,并采用相关分析、通径分析、主成分分析探讨了酶活性和土壤养分的关系。结果表明：稻草覆盖与间作三叶草能显著提高丘陵茶园土壤有机质、全N及速效P、速效K含量,间作三叶草明显增加土壤过氧化氢酶、转化酶含量,而稻草覆盖明显增加磷酸酶和脲酶活性。相关分析表明,土壤过氧化氢酶、脲酶、蔗糖酶、磷酸酶均与全氮、有机质、速效N呈极显著或显著正相关。通径分析表明,与4种酶关系最直接的是有机质或全N。主成分分析表明,土壤过氧化氢酶、脲酶、蔗糖酶、磷酸酶活性在第1主成分内的权重分别为0.842、0.937、0.873和0.847,可见,过氧化氢酶、脲酶、蔗糖酶、磷酸酶活性可用于评价丘陵茶园土壤C、N肥力。     

复合茶园光照强度的研究

复合茶园能提高茶叶的产量和质量已是不争的事实．然而复合茶园内的光照强度必须符合茶树生长发育需要，过强或过弱都将影响茶叶的产量和品质．因此，研究复合茶园内的光照强度具有重要的理论与实践意义．而计算茶园内各点的光照强度的关键问题是要解决间作树的消光率，通过间作树冠层消光率的计算就可算出茶园各点的光照强度，以作复合茶园设计和调控之依据.     

不同栽培模式对茶园生态环境及茶叶品质的影响

对陕南茶区的纯茶园、塑料大棚茶园、松茶间作茶园及林篱茶园4种常见栽培模式的茶园生态环境(包括小气候因子、土壤因子)和茶叶中各项生化指标(包括氨基酸、咖啡碱、茶多酚、酚氨比、茶水浸出物)进行了测定.结果表明:不同栽培模式茶园小气候因子有显著差异.相对于纯茶园,塑料大棚茶园、松茶间作茶园和林篱茶园能更有效地改善光照条件、降低环境温度、提高土壤水分和有机质含量、增强空气湿度,提高土壤养分状况.3种复合式茶园茶叶品质也较纯茶园显著提高,氨基酸和茶水浸出物含量显著高于纯茶园茶叶,而茶多酚含量却显著低于纯茶园茶叶.因此,林茶复合栽培模式和大棚模式茶园的生态环境更有利于茶树的生长和茶叶品质的提高.     

湿地松与茶树间作根系分布状况的研究

湿地松(Pinus elliottii)是阳性乔木,茶树(Camellia sinensis)是阴性灌木。这两种树种间作,形成针阔、乔灌两层树冠结构的茶园复合生态系统,可以改善茶树生态条件,提高茶叶的产量和品质。但间作存在胁地现象。一般认为这是上层树木的过度遮荫和根系间的竞争造成的。为了解这两种树种根系的分布状况和相互关系,并为间作茶园的合理配置和加强这种茶园的耕作管理提供依据,我们进行了湿地松与茶树间作根系分布状况的研究。     

不同管理模式对茶树碳氮磷含量及其生态化学计量比的影响

植物不同器官的碳(C)、氮(N)、磷(P)含量及其生态化学计量特征能够反映植物内部的养分分配与平衡关系。该研究以福建安溪3种不同管理模式的铁观音茶园为研究对象, 设置了常规管理模式下的茶园(M1)、间作套种模式下的茶园(M2)和现代技术管理模式下的茶园(M3) 3种样地, 分析茶树根、茎、叶器官的C、N、P含量及其化学计量学特征, 养分的变异特征与异速生长关系。结果表明: M2和M3管理模式下茶树根、茎、叶N、P含量均显著高于M1管理模式, C含量差异不明显; 茶树根、茎、叶C:N、C:P、N:P均表现为M1 > M2 > M3。茶树不同器官C、N、P含量差异较大, 根据变异来源分析, 管理模式因素对C、N、P含量变异的影响均达到显著水平。根茎叶N-P的异速生长关系表明茶树不同器官的养分需求存在相似性; 土壤pH和容重是影响C:N、C:P、N:P的重要因素, 而土壤含水量和盐度对茶树根和叶C含量的影响较大。总体来讲, 间作套种以及现代化滴灌、水肥等管理模式可以改善茶树对养分的吸收效率, 对解决土壤养分不均衡问题具有正面效应。     

茶稻间作系统的生态结构特征及生理特性研究

茶稻间作系统叶面积指数高于单作茶园,且上、下２ 层空间分布合理,水稻生长前期形成上部茶冠和下部水稻的生态边界层,生长后期则形成上部水稻和下部茶冠的生态边界层,有利于系统对光、热、水、气资源的充分利用．比之于单作茶园,茶稻间作系统内盛夏期相对光强减弱３５７ ％ ,午后温度降低０９ ～１９ ℃,相对湿度增加７ ％ ,为茶树生长提供了较适宜的生态环境条件,新梢生长速率有所提高．茶稻间作系统中的水稻比水田水稻水分利用率高,边际效应显著,有效穗数增加,结实率提高     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Chemical constituents from the fruits of Rhus typhina L. and their chemotaxonomic significance

This work describes the isolation and characterization of twenty-nine compounds from the fruits of Rhus typhina L., including eleven flavonoids (1–11), eleven phenols (12–22), two pentacyclic triterpenes (23–24), two organic acids (25–26), one lumichrome (27), one courmarin (28) and one pyrimidine (29) on the basis of their spectroscopic data. Compounds apigenin (1), daidzein (4), orobol (5), 3′, 5, 5′, 7-tetrahydroxyflavanone (6), naringenin (7), butein (8), (-)-catechin (9), quercetin-3-O-α-L-(3″-O-galloyl)-rhamnoside (11), 2-hydroxybenzoic acid (13), 4-hydroxybenzaldehyde (14), vanillin (15), methyl 3,4-dihydroxybenzoate (16), 3,5-dihydroxybenzamide (18), tyrosol (19), caffeic acid (20), 3-(2,4,6-trihydroxyphenyl)-1-(4-hydroxyphenyl)-propan-1-one (21), phlorizin (22), friedelin (23), oleanolic acid (24), 4,4-dimethyl-heptanedioic acid (25), anthranilic acid (26), lumichrome (27), scoparone (28) and uracil (29) have not been recorded before in this plant. This is the first report on the occurrence of compounds 4–7, 9, 11, 13–14, 16, 18–21, 25–29 from the genus Rhus. Moreover, the chemotaxonomic significance of these isolated compounds was also summarized.