滇中常绿阔叶林凋落物养分释放及生态化学计量特征对模拟N沉降的响应

为研究N沉降下凋落物养分释放及生态化学计量特征,以滇中磨盘山常绿阔叶林为研究对象,利用尼龙网袋法布设凋落物(凋落叶、凋落枝)原位分解试验,设置不同施N处理:对照(CK,0 g N·m^-2·a^-1)、低氮(LN,5 g N·m^-2·a^-1)、中氮(MN,15 g N·m^-2·a^-1)和高氮(HN,30 g N·m^-2·a^-1)。结果表明: 模拟N沉降1年后,凋落叶、凋落枝和土壤的C、N含量均表现为随着N沉降量的增加而逐渐升高,增幅分别为0.3%～8.2%、4.9%～69.0%;C/N则表现为随着N沉降量的增加逐渐降低,降幅为0.8%～37.8%;凋落枝P含量、C/P、N/P在各处理下差异均不显著。处理时间与施N水平均显著影响凋落叶、凋落枝及土壤的N、P含量及C/N、C/P、N/P;1年分解过程中,凋落物C、N、P残留率依次呈释放、淋溶-富集-释放、淋溶-富集的模式,外源N显著抑制了凋落物C、N、P释放过程;土壤C、P含量与凋落物N、P含量呈显著正相关,土壤N含量与凋落物C、N含量呈显著正相关。N沉降下常绿阔叶林凋落物与土壤生态化学计量具有显著相关性,研究滇中常绿阔叶林凋落物分解和生态化学计量特征有助于了解森林生态系统凋落物分解过程对N沉降的响应机理。     

大兴安岭不同火烧年限森林凋落物和土壤C、N、P化学计量特征

测定大兴安岭林区不同火烧年限(火后4、14、40、70和120年内未火烧)、不同坡度(坡地、平地)凋落物和土壤C、N、P含量及其化学计量比,分析火烧对凋落物和土壤养分的长期影响及两者之间的关系.结果表明: 不同火烧年限凋落物和土壤C、N、P化学计量特征差异显著,凋落物C含量变化不大.凋落物N、P含量随火烧年限的增加而增加,在火后4和14年较低,在火后40年恢复到对照(未火烧)水平.凋落物C∶N和C∶P值随火烧年限增加而下降,N∶P值则呈上升趋势.土壤C、N、P含量及其比值随土层深度增加而降低.坡地土壤C含量随火烧年限增加而增加,在火后70年显著高于对照,在平地差异不显著.火烧年限和坡度的交互作用影响土壤P含量和C∶P值.坡地土壤P含量在火后4年高于对照,而平地在火后40年高于对照;坡地C∶P值在火后14年达到对照水平,而平地与对照差异不显著.冗余分析表明,有机质层土壤的坡度效应大于年限效应,矿质层土壤主要受年限效应影响.火后4和14年凋落物及土壤养分含量低于对照,随着火烧年限的增加,植被生长迅速同时凋落物分解加快,凋落物质量及土壤养分质量不断提高,在火后40年恢复到未火烧水平,趋于稳定状态.     

冰雪灾害对杉木林土壤特性的影响

2008年初,在波及我国南方大部分地区的雨雪冰冻灾害中,冻雨在杉木枝叶上形成冰柱,造成大量的杉木个体折冠。通过开展杉木林凋落物和树干残体的养分及土壤理化性质的研究,可以了解冰雪灾害后杉木林的土壤肥力动态。冰雪灾害造成的林冠折损引起了林地的光照增强,导致了土壤温度上升及土壤水分增加,从而促进了凋落物的分解,凋落物经过1a的分解后,N、P和K含量分别下降了7%、12%和21%。凋落物储量减少了22%,N、P和K的储量分别下降了27%、31%和38%。2009年树干残体的N和P含量分别上升5%和6%,而K含量降低15%。树干残体由于分解缓慢,其储量下降3%,N储量增加了2%,P储量不变,而K储量下降了18%。冰雪灾害后森林凋落物积累于地表,分解后形成较厚的有机质层,土壤结构因此变得疏松。2009年的土壤容重和毛管孔隙度减小,总空隙度和毛管持水量增加,非毛管孔隙显著增加。林冠残体在分解过程中促进了土壤有机质和养分的积累。2009年的土壤pH降低,有机质、全N、全P和全K含量分别增加了16%、11%、14%和8%,碱解N和速效P含量分别增加了113%和17%,而速效K含量下降了36%。     

不同林龄马尾松凋落物基质质量与土壤养分的关系

凋落物的质量、数量及分解速率在一定程度上代表了土壤的营养状况。为了精确估算凋落物分解对土壤碳库的年净归还量及凋落物-土壤生物化学连续体的深层理解,从凋落物基质质量的角度分析了三峡库区不同林龄马尾松凋落物基质质量与土壤养分的作用关系,结果表明:中龄林、近熟林、成熟林马尾松凋落物基质质量中的C、C/N比、C/P比、木质素/N比、木质素/P比差异显著,其中近熟林凋落物叶木质素/N分别比中龄林和成熟林的高33.65%、39.24%,N、P、K、木质素含量差异不显著;但各组织器官的N、P、K含量差异显著,均是皮<枝<叶<杂物,C/N比、C/P比的变化则相反。不同林龄马尾松0-20 cm(0-5 cm、5-10 cm、10-20 cm)土壤有机质、总氮、有效磷含量均表现出近熟林<中龄林<成熟林,0-5 cm最大,10-20 cm最小,且随着土壤深度的增加而明显降低,总磷则是中林龄最低,成熟林最大,pH值则各土层均表现为中龄林<成熟林<近熟林,平均pH值为4.55-5.51。凋落物基质质量指标与土壤养分之间冗余分析(RDA)表明:马尾松凋落物基质质量和土壤养分之间关系紧密,N、P、纤维素、半纤维素、木质素、木质素/N比、C/N比对土壤养分影响比较大;凋落物中木质素/N比、C/N比与土壤有机质呈显著负相关,其含量越高越不利于土壤有机质的形成,土壤养分积累的越慢;凋落物基质质量氮含量与土壤氮含量呈显著正相关;土壤pH值、容重与N含量呈显著负相关,与凋落物C/N比、木质素/N比呈显著正相关。马尾松土壤表面有机质、N、P养分含量与凋落物基质质量对应养分含量变化规律一致,土壤养分高,凋落物基质质量相对较高,土壤贫瘠,凋落物基质质量相对较低。     

中亚热带常绿阔叶林凋落物分解过程中汞的动态变化及迁移机理

森林凋落物对于汞在林地土壤的生物地球化学循环中起到重要作用,为研究森林凋落物分解过程中汞的迁移转化特征,以重庆四面山风景名胜区典型林分(常绿阔叶林)作为研究对象。于2014年3月—2015年3月连续监测典型林分凋落物中各形态汞浓度和有机质变化量,同时监测周围土壤中汞浓度变化。结果表明:四面山典型林分凋落物分解过程中汞浓度整体上升,总汞浓度(初始浓度:78 ng/g)的增幅最高达53%,甲基汞浓度(初始浓度:0.32 ng/g)最高增幅达138%;在春季和夏季,水溶态和酸溶态两种活性态汞含量分别增加了851%和96%,在分解前期和末期,凋落物汞的中惰性汞比例最高,占比达75%。土壤腐殖质层中总汞和甲基汞浓度比较稳定。凋落物中活性态汞通过雨水淋洗进入土壤与有机质络合并发生甲基化/去甲基化过程,通过地表径流、地下径流进入水体。凋落物中C含量减少了22%,N含量增加了15%,总汞浓度与C/N比呈负相关,与N含量呈正相关。凋落物中微生物C、N含量整体增加,与汞浓度峰值同步,且夏季含量显著高于冬季含量(P0.05),说明微生物与凋落物固定汞和汞的甲基化过程密切相关。     

林下层植物在退化马尾松林恢复初期养分循环中的作用

以鼎湖山退化马尾松 (Pinusmassoniana)林恢复过程中林下层植物凋落物、分解和养分动态为对象 ,研究了林下层植物在退化马尾松林恢复初期养分循环中的作用。结果表明 ,林下层年凋落物量除在第 5年有所下降外均随时间逐年上升 ,但其增加速率随年份不同而异 ,总平均年增长速率为 3 8%。第 4年凋落物量为 0 .2 0 t· hm- 2 · a- 1,第 1 1年为 1 .1 7t·hm- 2·a- 1。凋落物养分元素平均浓度为 (% ) :N0 .95 ,P0 .0 4,K0 .5 7,Ca0 .1 3和 Mg0 .0 8,基本上以夏季和秋季最高冬春交替月份最低。第 1 1年凋落物各元素养分归还量为 (kg· hm- 2·a- 1) :N1 1 .1 0 ,P0 .47,K6.65 ,Ca1 .48和 Mg 0 .91。凋落物在分解过程中失重率呈直线模型变化 ,第 1年的分解速率为 3 1 % ,至试验结束时凋落物的残存量占起始量的 66%。在凋落物分解过程中 ,N和 P浓度随时间逐渐上升 ,但 N增加的速度较 P快 ,其余元素浓度均下降 ,但 K下降的速度最快。在凋落物分解过程中 ,N是唯一表现残留量呈先上升然后下降变化的元素。P的残留量变化与凋落物的失重率变化几乎一致。各元素在分解试验结束时残留量占起始量的百分比分别为 :N 90 % ,P 67% ,K 9% ,Ca 3 0 %和Mg 1 4%。可见 ,林下层凋落物在退化马尾松林恢复初期碳及其它营养元素循     

三峡库区典型流域退耕地植物种类及凋落物对土壤有机碳固定的影响

研究三峡库区典型流域退耕地植物种类和凋落物对土壤有机碳(SOC)固定和迁移的影响.2008年设计C3植物处理(A1)、C4植物香附子无凋落物处理(B0)和双倍凋落物处理(B2)裂区试验,2010年分层采集土壤和植物样品,测定SOC碳密度和稳定性碳同位素δ13C值的变化.结果表明:三峡库区典型流域退耕地土壤SOC密度由于土地利用的变化均发生了变化,退耕2年后,A1区内0～ 30 cm层内SOC量持续增加,平均增加了58.4 g·m-2(1.1％);C4处理的无凋落物区B0,SOC密度增加最为显著,为303 g·m-2(4.9％),但双倍凋落物区B2,SOC密度降低了79g·m-2(1.1％).凋落物对SOC密度影响显著(P＜0.05).     

氮磷添加对红壤区城郊湿地松林凋落叶分解的影响

城市化易导致城市森林氮(N)沉降和磷(P)富集,进而对凋落物分解过程产生影响。以位于南昌市郊的湿地松(Pinuse lliottii Engelm.)林为研究对象,采用尼龙网袋分解法,模拟N沉降(10g N·m-2·a-1,[N])、P积累(2.5g P·m-2·a-1,[P])和N沉降+P积累(10N·m-2·a-1+2.5g P·m-2·a-1,[N+P])对凋落叶分解速率与C、N、P含量及其化学计量比动态变化的影响。结果表明:与对照(CK)相比,[N]、[P]和[N+P]均促进凋落叶的前期(0～180d)分解速率,抑制中期(180～360d)、后期(360～540d)的分解速率;至540d时分解速率表现为[N]、[P]和CK无差异,但均高于[N+P](P0.05)。[N]提高分解过程中凋落叶N浓度,N含量表现为分解前期积累、后期释放;[P]提高分解过程中凋落叶P浓度,P含量持续积累;[N+P]提高N和P浓度,分解前期N、P含量积累,后期释放;而不同处理的C含量均表现为释放。凋落物基质C/N/P比与分解速率的相关性随分解阶段而表现各异。综合来看,城市化导致的N沉降和P富集叠加效应具有抑制城市森林凋落物分解过程的潜在性。     

地表覆盖栽培对雷竹林凋落物养分及其化学计量特征的影响

为了解不同覆盖栽培年限雷竹林凋落物养分及其化学计量特征,分析了换叶期雷竹林凋落物的凋落量,C、N、P、K养分含量,养分季节归还量以及养分元素生态化学计量比值在不同覆盖年限之间的差异。结果表明:(1)雷竹林在连续覆盖3a后,叶凋落量极显著性提高(P＜0.01),在总凋落量中比例增加,但枝凋落量变化不明显。(2)连续3a覆盖对雷竹林凋落物中的养分含量影响极显著(P＜0.01),C、N养分含量极显著降低,P含量极显著升高,而K养分含量在覆盖2a时就出现了显著增加的变化响应;林地凋落物的养分归还量同时还受凋落量的影响,其伴随覆盖年限增长的变化趋势与养分含量并不一致。(3)覆盖2a内的雷竹林地凋落物表现出稳定的高N∶P以及低P含量,表明凋落物分解速率较低;连续覆盖3a的林地凋落物P含量极显著升高,N∶P极显著下降(P＜0.01),表明此时凋落物分解速率加快。(4)线性回归分析表明,凋落物中K元素随覆盖年限增长而消耗的规律与N、P元素无显著相关关系。     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

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.