米心水青冈幼苗对光照和养分的响应

在模拟郁闭林下(L1,大约1%~2%的全日照)、林窗(L2,大约18%的全日照)、开阔地(L3,全日照)3个光照水平和每个光照水平下进行施肥(F1)和不施肥(F0)对照的6个实验处理条件下,研究了2年龄米心水青冈(FagusenglerianaSeem)幼苗在随后的两个生长季里的生长对光照和土壤养分的响应。结果显示:光照和养分对幼苗高度、基径和生物量有显著的影响。经过两个生长季,L1处理下幼苗高度增量极显著地小于L2和L3处理下幼苗高度增量。L1处理下基径和生物量的增量在处理当年秋就极显著地小于L2和L3处理下的增量,并在第二年差异继续扩大。L2和L3处理下的幼苗间的生长没有显著差异。施肥明显地促进了L2和L3处理下的幼苗的生长,但对L1处理下的幼苗没有明显的作用。这些结果说明,虽然2年龄米心水青冈幼苗能够在林下的弱光条件下生存,但生长受到了极大的抑制。幼苗在林窗的中等光照条件下能够与在开阔地全日照条件下生长的一样好或更好,这与许多耐阴的落叶树的响应一样。在比林内光照强度较高的条件下施肥或较高的土壤养分才对米心水青冈幼苗的生长和生存起作用。     

山地落叶阔叶林优势树种米心水青冈幼苗的定居

在郁闭的林冠下、模拟林窗和林间空旷地3种光照环境中,研究了施肥和未施肥的米心水青冈幼苗生存和生长发育过程．结果表明,幼苗在林下的发育受到光照不足的严重抑制,生长在林下的幼苗比生长在林窗和空旷地幼苗死亡快,死亡率高,幼苗在郁闭林下能够生存的时间不超过12周．施肥处理的幼苗比对照的幼苗死亡快,死亡率高．幼苗死亡很可能与土壤中的病原生物有关．虽然由林下光照强度增加到模拟林窗的光照强度后,幼苗发育有明显改善,但幼苗在模拟林窗环境和空旷地的生长没有显著差异．结果说明,米心水青冈新出土的幼苗在郁闭林冠下易受伤害,更新立苗阶段需要有比较好的光照条件,肥沃土壤可能也无助于改善郁闭林冠下幼苗的定居．     

林隙与林下环境对锐齿槲栎和米心水青冈种群更新的影响

锐齿槲栎 (Quercusalienavar.acuteserrata ) 和米心水青冈 (Fagusengleriana) 是广泛分布在我国暖温带和亚热带山地中海拔地段的主要建群种, 对水土保持和维持生态系统稳定具重要意义。该文通过在神农架地区的典型样地调查, 分析了这 2个种群在林隙和林下不同光环境中的更新状况和径级结构 ;利用便携式Licor₆ 4 0 0光合仪测量了 2种苗木的光饱和及光诱导曲线, 探讨了光对这 2个树种更新的影响机理。实验结果表明, 在所调查的林地中, 锐齿槲栎和米心水青冈种群都有充足的幼苗库, 锐齿槲栎幼苗以实生为主, 米心水青冈幼苗以萌生为主 ;从幼苗到幼树的转化过程中, 锐齿槲栎的成活率几乎为零, 而米心水青冈的成活率约为 6 %~ 8% ;在两者的混交林中, 米心水青冈种群呈稳定的金字塔形年龄结构, 而锐齿槲栎则是某一生长阶段的种群占据主导地位。光饱和曲线显示, 对 2年生同生群苗木, 在林窗下, 锐齿槲栎的最大净光合速率 (4.6 1μmol·m-2 ·s-1) 比米心水青冈的 (4.16 μmol·m-2 ·s-1) 要高 ;而在林冠下, 米心水青冈的最大净光合速率 (Pn=3.89μmol·m-2 ·s-1) 比锐齿槲栎的最大净光合速率 (Pn=3.6 8μmol·m-2 ·s-1) 要高。无论在林窗下或林冠下, 米心水青冈幼苗的光饱和点比锐齿槲栎的要低。两者混交林下的光诱导曲线显示, 与米心水青冈幼苗相比, 锐齿槲栎幼苗对光的反应速度较慢, 最大净光合速率也较低, 在林冠下表现出较弱的竞争力。资源分配试验证明, 锐齿槲栎在幼苗阶段以地上部分生长为主, 而米心水青冈倾向于把更多的干物质贮藏在根部, 显示出不同的光利用策略。     

长白山阔叶红松林不同演替阶段林下红松幼苗能量与养分季节动态

为了解林下红松幼苗生长和养分存储季节动态,以长白山原始阔叶红松林(原始林)和次生杨桦林(次生林)林下2年生红松幼苗为对象,研究林下光合有效辐射(PAR)、幼苗生物量、非结构性碳水化合物(NSC)、全氮(N)和全磷(P)等指标的季节变化,分析两林分林下光照的季节动态及其差异对红松幼苗生长和养分积累的影响。结果表明: 原始林和次生林林下月PAR累积量季节变化都呈“双峰”型,夏季为郁闭期,两林分林下光线弱。春季和秋季为阔叶树无叶期,林下光照条件变好,且次生林林下光照明显好于原始林;原始林和次生林红松幼苗的生物量、NSC、全N和全P浓度的季节动态与林下光照的季节变化基本一致,在春季和秋季表现为显著增加,在夏季呈下降趋势。春季幼苗的淀粉浓度增加,夏季淀粉和可溶性糖浓度均逐渐降低,到8月达到最低值,秋季可溶性糖浓度显著升高。春季和秋季次生林林下幼苗的生物量和NSC浓度整体上均显著高于原始林,而夏季两林分差异不显著。因此,春季和秋季的林下光照条件差异是影响原始林和次生林中红松幼苗养分积累和生长更新差异的主要原因。     

滇青冈幼苗的光合和生长对不同生长光强的适应

研究了3种光强(全日照的80%、20%和2%)下生长的滇青冈幼苗的光合-光强响应和生长状况。结果表明:3种光强生境滇青冈幼苗光饱和点和最大净光合速率没有显著差异,20%和2%生长光强下光补偿点显著低于80%生长光强。3种光强生境幼苗的光合饱和点在400~450μmol·m-2·s-1左右,光补偿点也很低(6~10μmol·m-2·s-1),表现出阴生植物的特征。但滇青冈幼苗较强的耐荫能力,是以牺牲生长为代价的。在2%的弱光生境中滇青冈幼苗比叶重显著降低,单位面积和单位干重叶绿素含量均显著增多,具有利用较强辐射的潜力,一旦林窗出现就可以利用增加的辐射提高光合速率,及时进入快速高生长。     

光照对珙桐幼苗光合与生长特性的影响

为了解珙桐幼苗对光强的适应性, 以3 年生珙桐幼苗为实验材料, 设置了全光照, 62%全光照及43%全光照3种光环境, 观测了110 d 后珙桐幼苗光合特性及生物量分配的变化情况。结果表明: (1)珙桐幼苗净光合速率(Pn)日变化在全光照条件下呈双峰型, 有明显“光合午休”现象, 而遮阴条件下呈单峰型; (2)遮阴处理下最大光合速率(Pmax)、表观量子效率(AQY)、水分利用效率(WUE)及光能利用效率(LUE)均高于全光照, 光补偿点(LCP)和暗呼吸速率(Rd)均低于全光照; (3)遮阴显著降低珙桐幼苗根冠比, 增加了比叶面积(SLA)和总生物量。上述结果说明: 遮阴处理后, 珙桐幼苗在光合特性和生长特性上表现出对弱光一定程度的驯化适应, 对比三种遮阴条件可以得知, 适度的遮阴更有利于幼苗的正常生长, 甚至在较低光照(43%全光照)环境下有更高的光能利用率。     

三峡地区柏木种子萌发和幼苗更新的研究

对三峡地区柏木(Cupressus funebris)林柏木种子的萌发、幼苗存活、幼苗生长进行了研究.结果表明,(1)柏木种子的萌动期约为10 d,播种35-45 d后进入萌发高峰期,柏木种子的平均萌发率为47.7%.土壤基质对种子萌发的影响是极显著的,光照对萌发则没有显著的影响.(2)幼苗平均死亡率为52.6%.土壤类型和光照强度对幼苗的存活都有显著影响,在林下土和80%光照条件下幼苗的存活率最高.(3)柏木幼苗生长初期茎的生长动态呈"S"型,而叶片数量的增长动态近于直线型.幼苗生长初期生物量形成主要受光照条件的影响,土壤类型的影响不显著.土壤和光照条件对柏木林柏木幼苗的更新都有显著影响,但是土壤条件主要影响种子萌发和幼苗的存活,而光照条件则主要对幼苗的生长和存活产生影响.     

水青冈林中两种鹅耳枥种子萌发和幼苗的生存与生长（英文）

 千金榆(Carpinus cordata var．chinensis)和千筋树(Carpinus fargesiana)是四川省北部山地水青冈林中的两种主要落叶阔叶树。两种植物种子萌发和幼苗生存与生长的实验研究结果显示：千金榆种子秋季成熟落地后有一年多的休眠期,种子主要在落地后的第二和第三个生长季萌发;千筋树种子成熟落地后有的可在来年萌发,但大部分是在第二个生长季萌发;由于每2～3年两种树就有一个较大的结实年,每年都会有一些新的幼苗在林中出土;尽管两种树是耐荫的,但幼苗在较好光照条件下(如林窗)生存和生长明显好于在林冠遮荫的地方;施肥会加速幼苗的死亡,特别是在阴暗的林下,但在光照较好的条件下能促进幼苗的生长。结果说明两种鹅耳枥的幼苗可以在林下持续存在,但只有在较好的光照条件下,如稀疏的林冠下或林窗下才会有明显的净生长。     

不同光环境下胡桃楸幼苗的形态可塑性及其响应研究

为了探求不同光环境对胡桃楸幼苗生长的影响,对全光照（100%光照）、中光照（60%光照）、低光照（30%光照）3种光环境下胡桃楸幼苗的生长、形态特征、生物量分配和水分特征开展研究。结果表明：胡桃楸幼苗的形态在不同光环境下存在明显的可塑性变化,生物量分配和水分特征均表现出不同程度的差异。低光照条件下,胡桃楸幼苗生长快,株高、地径分别为全光照的1.14、1.18倍;冠幅大,是全光照的1.40倍;叶片宽大,叶长和叶宽分别是全光照的1.25和1.36倍;分枝数明显少于全光照。3种光环境下胡桃楸幼苗地上部分生物量存在显著差异,地下部分差异不显著。叶片相对含水量随着光照的降低呈现逐渐增加的趋势;全光照条件下叶片饱和持水量与叶片干鲜比明显大于遮阴条件;3种光照条件下叶绿素含量差异显著。胡桃楸幼苗为适应不同光环境,在形态和生理方面都做出适应性调整,适当的遮阴处理有利于胡桃楸幼苗生长。     

神农架地区米心水青冈林和锐齿槲栎林群落干扰历史及更新策略

通过样地调查、树干解析及直径分析法,对神农架地区广泛分布的米心水青冈（ Ｆａｇｕｓｅｎｇｌｅｒｉａｎａ Ｓｅｅｍ ．） 林和锐齿槲栎（ Ｑｕｅｒｃｕｓ ａｌｉｅｎａ ｖａｒ． ａｃｕｔｅｓｅｒｒａｔａ Ｍａｘｉｍ ．） 林受压和释压历史及更新策略进行了研究。结果表明：米心水青冈直径生长表现为５ 种模式,而锐齿槲栎只表现为２ 种模式。（８５．９±６．９）％ 的米心水青冈有过受压过程,平均受压２ ．１±０ ．８ 次,平均受压时间为（４７ ±２４．１） ａ,最长受压时间７３ ａ,平均释压次数为１ ．６ ±０ ．７ 次,平均释压时间为（２３ ±２１．５） ａ,而６０．８３％ 的锐齿槲栎都均有１ 次受压,平均受压时间为（１９ ±１４） ａ,受压后没有表现出释压过程。结合高生长和径向生长,认为米心水青冈是耐荫树种,它的更新策略主要是在林下形成苗性萌枝,在有林窗形成时释压生长进入乔木层;而锐齿槲栎是不耐荫树种,其更新策略主要是通过产生大量种子,当有大的林窗时,幼苗在林窗内生长逐步进入乔木层     

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.