干旱区绿洲灌溉条件下不同树龄轮台白杏根系的空间分布

采用田间分层挖掘法和图像扫描分析法,研究了干旱区绿洲灌溉条件下不同树龄轮台白杏根系的空间分布特征.结果表明:轮台白杏的根系主要由细根(d≤1 mm)构成,中粗根(1＜d≤2 mm)和粗根(d＞2 mm)所占比例较小,树龄5 a、10 a和15 a轮台白杏细根长度分别占根系总长度的90.9％、88.4％和79.9％.随树龄延长,根长密度增加,不同径级根长密度均为15 a＞10 a＞5 a.在垂直方向上,轮台白杏的根长密度呈现出先增加后减小的分布趋势,且各土层根系干质量密度差异显著,树龄5a、10 a和15 a轮台白杏根系干质量密度分布较集中的区域分别为距离树干200 cm以内的30 ～ 80 cm、30～100 cm和30～100 cm深度土层,轮台白杏根系的水平分布特征为距离树干越远根系干质量密度越小,且距树干不同距离处的差异显著.从减小相邻树行间树体根系的交错重叠和降低水肥竞争的角度考虑,在干旱区绿洲灌溉条件下,轮台白杏的栽植行距应≥6 m.     

不同林龄胡杨克隆繁殖根系分布特征及其构型

以中龄林和成熟林胡杨为研究对象,采用挖剖面和根窗的方法,研究胡杨繁殖根系分布、根系构型,以及胡杨根蘖与繁殖根系构型之间的关系。结果表明:(1)细根(d<2 mm)的根长密度、根表面积密度,随深度增加呈现指数函数分布;(2)中龄林细根的根长密度、根表面积密度在0—90 cm各层都是显著大于成熟林的对应指标(P<0.05),成熟林的中等粗根(5 mm0.05),且两种林龄的一级侧根数、分枝角度亦无显著差异(P>0.05);(5)对比两种林龄不同根序上的根蘖芽发现,二级根上不定芽个数均是同组一级根上不定芽个数的3—4倍;基于以上对胡杨根系的功能权衡的分析,得出:细根对胡杨根系构型有重要的影响,在胡杨根系功能权衡中扮演重要角色。     

青杨人工林根系生物量、表面积和根长密度变化

在植物生长季节,采用钻取土芯法对秦岭北坡50年生青杨人工林根径≤2 mm和2～5 mm根系的生物量、表面积和根长密度进行测定.结果表明：在青杨人工林根系(＜5 mm)中,根径≤2 mm根系占总生物量的77.8%,2～5 mm根系仅占22.2%;根径≤2 mm根系表面积和根长密度占根系总量的97%以上,而根径2～5 mm根系不足3%.随着土层的加深,根径≤2 mm根系生物量、表面积和根长密度数量减少,根径2～5 mm根系生物量、表面积和根长密度最小值均分布在20～30 cm土层.≤2 mm根系生物量、表面积和根长密度与土壤有机质、有效氮呈极显著相关,而根径2～5 mm根系的相关性不显著.     

不同森林类型根系分布与土壤性质的关系

在红壤丘陵区选取8种典型森林类型,对不同土层深度、不同径级的根长密度分布特征、根长分维数,以及根系特征与土壤容重、有机碳、全氮的关系进行了研究。结果表明:马尾松低效林根长密度最小,杉木低效林和湿地松林较大,表层土壤根长密度与灌草覆盖度显著相关(r=0.793,P<0.05)。各种森林类型的根长密度随着土壤深度的增加均表现为递减规律,但随深度的增加,不同森林类型的差异逐步缩小,且植物种类及生长状况对根长密度分布的影响越来越小。在相同的土层中,根长密度随径级的变化并不一致,马尾松低效林0相似文献   

冬小麦根系分布规律

根据在郑州进行的冬小麦根系田间实测资料,研究了根长密度和根质量密度在砂壤土中的垂直分布.结果表明:冬小麦根量主要集中在上层,根长密度、根质量密度在0～50 cm土层内分别占57.7%和66.7%,而在50～100 cm层分别占23.4%和18.7%,根长密度和根质量密度随土壤深度的变化均符合指数函数形式;综合考虑根量分布、根系吸水等因素,确定了冬小麦适宜的底墒深度为100 cm.     

漓江水陆交错带典型立地根系分布与土壤性质的关系

研究根系与土壤关系是发掘河岸带生态退化等问题内在原因的重要途径。在漓江流域水陆交错带选取缓坡、陡坡、江心洲、人工岸坡4种典型立地类型,对不同土层深度的根长密度、根系生物量、比根长,以及根系特征与土壤有机质、全氮、有效磷的关系进行了研究,旨在为漓江流域生态修复过程中植被恢复、植被配置、快速绿化材料选取提供科学依据。结果表明:(1)同一立地类型0—10 cm土层和10—20 cm土层比根长差异性不显著。0—10 cm到10—20 cm土层,各立地类型根长密度和根系生物量密度均减小,但不同立地类型根长密度和根系生物量密度的差异程度逐渐缩小,表明地形、地表植物类型及生长状况对根长密度分布的影响也随土层深度的增加而逐渐减小。细根根长和生物量随着土壤深度的增加而减小。(2)土壤有机质含量差异性显著,分布规律为人工岸坡陡坡江心洲缓坡;土壤全氮含量从大到小依次是人工岸坡、陡坡、缓坡、江心洲,其值分别为:3.12、2.33、1.56、1.32 g/kg;土壤全氮与土壤有机质呈显著正相关。江心洲和缓坡有效磷含量远远大于人工岸坡和陡坡,原因是漓江水长期受人为洗漱影响,导致受江水干扰大的立地类型有效磷含量高。(3)根长密度、比根长、根系生物量与有机质、全氮含量呈正相关,与有效磷含量呈负相关,说明土壤根系越丰富,越有利于增加土壤有机质和全氮含量,但遏制了土壤有效磷。细根长度、生物量与根长密度在0.01水平(双侧)上显著正相关,与根系生物量密度呈负相关。     

滨岸不同植物配置模式的根系空间分布特征

崇明岛位于长江河口,是世界上最大的冲积岛。滨岸植物配置模式对防止侵蚀、坍塌等具有不同的作用。以崇明岛南岸4种不同的植物配置模式:芦苇(Phragmites australis)-海三棱藨草(Scirpus mariqueter)模式(PSM)、池杉(Taxodium ascendens)-芦苇-海三棱藨草模式(TAPSM)、杂交柳(Salix matsudana×alba)-芦苇-海三棱藨草模式(SPSM)及落羽杉(Taxodium distichum)-芦苇-海三棱藨草模式(TDPSM)为对象,对不同植物配置模式在低、中、高3个潮位根系空间分布进行了调查和分析。结果表明:(1)4种模式中0-40cm土层内平均总根长最大的为SPSM模式,其值为137.0cm/cm2,平均总根长最小的为TAPSM模式(91.4cm/cm2);在3种乔木增配模式中,草本植物根长占总根长比例达94.6%-98.1%。(2)除SPSM模式外,其他3种植物配置模式根长密度均随土层加深而减小,这3种模式根长密度最大的土层皆为0-10cm土层,分别为各自最底层根长密度的15.1倍(PSM)、4.9倍(TDPSM)和2.0倍(TAPSM);SPSM模式在10-20cm土层根长密度最大。(3)在所有4种模式中,直径Φ0.1mm的微细根对总根长密度的贡献均为最大,比例从74.7%到81.7%,其次为直径0.1mm≤Φ1mm的细根,直径Φ≥5mm的大根极少。(4)秩和检验显示,4种模式在低、中、高3个潮位根长密度的差异并不一致。根系能够提高土壤抗侵蚀能力,研究4种模式根系空间分布特征,可以为崇明岛滨岸植物配置,建设抗蚀护滩植被带提供科学依据。     

不同分类系统下油松幼苗根系特征的差异与联系

植物根序和径级不仅反映细根的形态结构, 而且能反映根系的一些生理特征, 如细根寿命和周转等。该文以二年生油松(Pinus tabulaeformis)幼苗根系为研究对象, 系统比较了根序分类方法和径级分类方法在描述根系特征上的优缺点, 探索了两者之间的内在联系。结果表明: 二年生油松幼苗最多可包括6级根序, 直径的变化范围为0.169-3.877 mm。按根序划分, I-VI级根序的总根长和总根表面积主要集中在前3级根序, 这3级根序的根占总根长的78.77%和总根表面积的62.72%。前3级根序的比根长是后3级根序比根长的1.3-3.0倍, 比根面积是后3级比根面积的1.0-1.5倍。按常用的径级(以0.5、1.0、1.5和2.0 mm为阈值)划分方法, 油松幼苗大部分根系直径≤1.5 mm, 此区间细根的根长和根表面积占总根长的93.76%和总根表面积的84.35%。直径≤1.5 mm的细根平均比根长是>1.5 mm细根比根长的3-7倍, 比根面积的1.5-3.0倍。由于油松根序和径级之间有显著的指数关系, 依据径级最大程度反映根序的原则, 提出了新的径级划分方法, 即以0.4、0.8、1.3和2.0 mm为阈值对油松幼苗根系径级重新进行划分。此时, 上述区间可分别包括I级、II级、III级、IV级、V级根序中根尖数的93.22%、86.37%、75.96%、70.47%和76.67%。同时也可分别涵盖各径级根长的89.34%-70.83%、根面积的86.01%-76.12%以及体积的87.73%-76.12%。此时, 根系不同径级与根序之间可以建立起良好的对应关系。这些结果表明, 通过合理划分径级区间可以较好地反映根序 特征。     

冬小麦根系分布规律

根据在郑州进行的冬小麦根系田间实测资料,研究了根长密度和根质量密度在砂壤土中的垂直分布。结果表明:冬小麦根量主要集中在上层,根长密度、根质量密度在0～50 cm土层内分别占57.%和66.%,而在50～100 cm层分别占23.%和18.%,根长密度和根质量密度随土壤深度的变化均符合指数函数形式;综合考虑根量分布、根系吸水等因素,确定了冬小麦适宜的底墒深度为100 cm。     

不同耐盐品种棉花根系主要指标对盐分胁迫的响应

以盐敏感品种‘中棉所45’(CCRI45)、弱耐盐品种‘新陆早17号’(XLZ17)、中等耐盐品种‘新陆早13号’(XLZ13)和耐盐品种‘中棉所35’(CCRI35)为试验材料,利用根系分析系统研究盐分胁迫下棉花根系形态特征及其与棉株耐盐性的关系.结果表明:盐分胁迫显著降低棉花根和叶的干质量以及K^+/Na^+,其中耐盐品种CCRI35和中等耐盐品种XLZ13的根干质量、叶干质量以及根中K^+/Na^+分别比盐敏感品种CCRI45提高了69.3%~104.4%、24.8%~45.3%和25.0%~45.8%;盐分胁迫显著抑制棉花根系生长发育,其中CCRI 35和XLZ13的总根长、根系总表面积、根系总体积以及0~10 cm土层中直径为0~1.2 mm内的根长、根表面积和根体积均显著高于CCRI45,分别增加了15.2%~85.8%、12.0%~68.5%、31.7%~217.8%、27.2%~73.9%、39.6%~74.3%和99.0%~309.7%.主成分分析表明,比根长、浅层根长比例和细根比例受基因型差异的影响较为明显,是区分不同耐盐品种棉花根系形态差异的主要指标.逐步回归分析显示,比根长、0~10 cm土层的粗根根长、细根根表面积、粗根根表面积、粗根体积、中根比例,以及10~20 cm粗根根长、粗根表面积、粗根体积等根系参数对盐分响应敏感.耐盐棉花品种可通过维持表层根长比例、细根比例和比根长的增加来适应盐分胁迫.     

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.     

Enterovirus 71 3C proteolytically processes the histone H3 N-terminal tail during infection

Highlights
1. The N-terminal tail of histone H3 is specifically cleaved during EV71 infection.
2. Viral protease 3C is identified as a protease responsible for proteolytically processing the N-terminal H3 tail.
3. Our finding reveals a new epigenetic regulatory mechanism for Enterovirus 71 in virus-host interactions.     

Detection of EBV and HHV6 in the Brain Tissue of Patients with Rasmussen’s Encephalitis

Rasmussen’s encephalitis (RE) is a rare pediatric neurological disorder, and the exact etiology is not clear. Viral infection may be involved in the pathogenesis of RE, but conflicting results have reported. In this study, we evaluated the expression of both Epstein-Barr virus (EBV) and human herpes virus (HHV) 6 antigens in brain sections from 30 patients with RE and 16 control individuals by immunohistochemistry. In the RE group, EBV and HHV6 antigens were detected in 56.7% (17/30) and 50% (15/30) of individuals, respectively. In contrast, no detectable EBV and HHV6 antigen expression was found in brain tissues of the control group. The co-expression of EBV and HHV6 was detected in 20.0% (6/30) of individuals. In particular, a 4-year-old boy had a typical clinical course, including a medical history of viral encephalitis, intractable epilepsy, and hemispheric atrophy. The co-expression of EBV and HHV6 was detected in neurons and astrocytes in the brain tissue, accompanied by a high frequency of CD8⁺ T cells. Our results suggest that EBV and HHV6 infection and the activation of CD8⁺ T cells are involved in the pathogenesis of RE.     

Perinatal Vertical Transmission of Chikungunya Virus in Ruili,a Town on the Border between China and Myanmar

正Dear Editor,Chikungunya virus (CHIKV), an arbovirus in the family of Togaviridae, genus Alphavirus, is transmitted by the A.aegyptii or A. albopictus mosquito, and causes disease in humans characterized by fever, rash, and arthralgia (Silva and Dermody 2017; Suhrbier 2019). It was first reported in 1953 in Tanzania, and caused only a few outbreaks and sporadic cases in Africa and Asia in last century. However, in the epidemic in 2004, CHIKV acquired mutations that conferred enhanced transmission by the A. albopictus mosquito(Schuffenecker et al. 2006). Since then, it has successively caused outbreaks in Africa, the Indian Ocean, South East Asia, the South America, and Europe (Zeller et al. 2016).     

Development of a Novel Reverse Transcription Loop-Mediated Isothermal Amplification Method for Rapid Detection of SARS-CoV-2

In conclusion, the novel visual RT-LAMP assay is a simple, rapid, and sensitive approach for detection of SARS-CoV-2, and it is ready for application in primary care and community hospitals or health care centers, and even patients' own houses in response to the current SARS-CoV-2 epidemic because the assay does not require sophisticated equipment and skilled personnel. Furthermore, it is also ready to be used in fields for screening samples from wild animals and environments to facilitate the identification of potential intermediate hosts that mediate the cross-species transmission of SARS-CoV-2 from bats to humans.