江西马头山自然保护区攀缘植物区系研究

马头山自然保护区位于江西省东部资溪县的马头山林场内,地理坐标为117°08’52”～117°18’00”E, 27°40’43”～27°53’52”N,总面积为21 570 hm2,有丰富的野生攀缘植物资源。通过野外采集及标本的整理鉴 定,初步确认该区共有攀缘植物40科92属222种(包括种下等级)。根据对马头山攀缘植物区系分析的结 果,指出本区攀缘植物区系具有以下特征:(1)种类组成丰富,地理成分复杂;(2)区系中热带性地理成分占主 导地位;(3)区系成分相对古老,特有类群丰富,多型性突出;(4)华东区系特征明显,南北区系过渡。     

Diversity of climbing seed plants and their reproductive habit in a karst seasonal rain forest in Nonggang,Guangxi, China

Aims Diversity of climbing seed plants and their reproductive habits and characteristics are central for the understanding of community structure and dynamics of forests and hence are important for forest protection. However, little is known about the climbing seed plants in northern tropical karst seasonal rain forests. Here, using the data of the species diversity and reproductive habits of climbing seed plants in Nonggang, Guangxi, China, we aim to 1) explore the species diversity and distribution of climbing seed plants in northern tropical karst seasonal rain forests, 2) study the flowering and fruiting phenology and 3) the associations of reproductive characteristics to the environment. Methods Species composition, preferred habitat, flowering time, fruiting time and fruit types of climbing seed plants were surveyed. The seasonality of flowering and fruiting were analyzed by concentration ratio and circular distribution. Climbing seed plants were divided into three groups according to their growth forms and places in spatial forest structure: bush ropes, herbaceous vines and lianas. Monthly flowering ratios, fruiting ratios, fruit types and their ratios in different groups were determined. These relationships of flowering ratio, fruiting ratio, fruit type and its ratio to meteorological factors were investigated using Pearson correlation analysis. Important findings There were a total of 333 species of climbing seed plants in Nonggang karst seasonal rain forest, belonging to 145 genera and 56 families. Bush ropes, herbaceous vines and lianas contained 119, 88 and 126 species, respectively. At species level, herbaceous vines were more abundance in valleys, while bush ropes and lianas were more abundance on slopes. Flowering and fruiting of climbing seed plants occurred seasonally, with flowering peaking in April to September, while fruiting peaking in July to December. The seasonality of flowering and fruiting in bush ropes was weaker than in herbaceous vines and lianas. Flowering ratio was significantly positively correlated with rainfall and air temperature, which suggest that flowering peaks in monsoon season. Peak time for fruiting was about three months later than the peak time of flowering, around the end of monsoon season. The ratio of samara species to all fruiting species in lianas was significantly positively correlated with wind speed, but negatively correlated with rainfall and air temperature. It showed that samara in lianas tended to occur in dry season with high wind speed. In conclusion, species diversity and the seasonal features of reproduction of climbing seed plants in Nonggang karst seasonal rain forest were closely related to the spatial and temporal variations of habitat resources.     

喜马拉雅地区藤本植物多样性及其地理格局

喜马拉雅山地是生物地理学研究的热点地区之一。本文对喜马拉雅地区的藤本植物多样性及其与毗邻地区的联系进行了统计分析, 并对该地区与印度河-恒河平原地区藤本植物多样性的地理格局及其成因进行了研究。结果显示: (1)喜马拉雅地区总计有1,083种藤本植物, 分属72科309属; 其中木质藤本725种, 草质藤本358种; 攀援方式主要为缠绕攀援(51.3%)。(2)该区域的藤本植物组成受相邻区域植物区系的显著影响, 其1,083种藤本植物中有74.1% (802种)在东南亚地区有分布, 50.6% (548种)在南亚有分布, 48.9% (530种)在中国西南地区有分布。本区藤本植物缺乏特有性, 仅125种(11.5%)为本区所特有, 没有特有含藤属。(3)藤本植物多样性及其在植物区系中的比例均自东向西逐渐降低; 木质藤本比例和缠绕攀援藤本比例均自东向西略呈上升趋势; 大多数含藤属的藤本多样性由东往西递减, 仅极少数含藤属由东往西逐渐增加, 如野豌豆属(Vicia)和菟丝子属(Cuscuta)。(4)藤本植物多样性在喜马拉雅和印度河-恒河平原地区呈现出自东向西递减的相似格局, 由东往西方向上含藤属递减率分别为8.4属/100 km和6.3属/100 km, 但喜马拉雅地区藤本植物多样性更高。喜马拉雅和印度河-恒河平原地区均有分布的272个含藤属中有196属在中亚及伊朗高原不再有分布, 其中31.1% (61属)在喜马拉雅地区的分布显著更偏西, 仅4.1% (8属)在印度河-恒河平原的分布显著更偏西。综合分析表明, 喜马拉雅地区藤本植物的多样性及其地理格局的特点与其特殊的地理位置、气候条件和生境的梯度变化以及毗邻地区植物区系的多元化有关; 水分条件的东西向梯度变化可能是藤本植物在喜马拉雅和印度河-恒河平原地区形成相似格局的主要原因。     

华中地区藤本种子植物区系的研究

以湖南和湖北两省为代表对华中地区藤本种子植物的区系进行了研究。本区共有藤本种子植物62科175属838种,其中土著种类有60科159属784种。在科、属、种的水平上对藤本种子植物区系特性进行了较深入的统计和分析,并对本区藤本种子植物与邻近地区的关系、本区内的藤本种子植物的地带性分异进行了探讨。统计表明,本区藤本种子植物种数占该区种子植物总种数的11%,且61.7%的种类主要集中在30种以上的大科中;热带分布型明显多于温带分布型;泛热带、热带亚洲、东亚（中国）特有和东亚—北美间断分布科属比较集中,其中许多属为古老成分;本区藤本种子植物特有成分丰富,计有东亚特有科1科、中国特有属6属、中国特有种507种（其中华中地区特有种35种）。通过研究认为：本区藤本种子植物具有种类丰富、分布类型多样、特有成分较多、区系较古老的特点;与本区的全部种子植物区系相比,藤本种子植物区系的热带性更强,具有明显的热带亲缘性,并与喜马拉雅及中国西南有较强的地理渊源。     

Standardization of seed storage conditions in chilgoza pine (Pinus gerardiana Wall.): an endangered pine of Hind Kush Himalaya

The seeds of chilgoza pine (Pinus gerardiana) show moderate germination and not retain better germinability under normal ambient storage. In the present study, five storage containers [polythene bags (C₁), plastic jars (C₂), canvas bags (C₃), earthen pots (C₄) and tin boxes (C₅)] and four temperature regimes (19–22 °C) (room temperature, T₁), 0 ± 1 °C (T₂), ?4 ± 1 °C (T₃) and 4 ± 1 °C (T₄) were tested and the suitable seed storage conditions of chilgoza pine to retain viability were standardized. The storage devices preserve and retain viability trend of C₄ > C₃ > C₁ > C₂ > C₅ and T₂ > T₃ > T₄ > T₁ in the species throughout the storage period. However, the interaction treatment (C₄T₂) of earthen pots under 0 ± 1 °C temperature regime maintained significantly (P < 0.05) maximum germinability after 9 months (58.3 %) followed by C₃T₂ and C₄T₃ (47.5 %) as compared to other storage conditions. Notably, a sharp decline in germinability was recorded in seeds stored in tin boxes placed at room temperature. The implementation of these results for conservation management, especially nursery development and sustainable utilization of P. gerardiana in Himalayan region, has been suggested.     

中国种子植物区系中的藤本多样性

藤本植物是植被的重要组成部分,但由于野外考察中物种及无性系分株鉴定的困难,长期以来在生态学研究中常常被忽视。为揭示中国藤本植物的多样性和特有性,作者研究了其科属组成、区系成分和攀援方式。结果显示:中国藤本植物种类丰富,共计有85科409属3,073种(含变种、亚种),占中国种子植物区系的11.3%;其中草质藤本898种,木质藤本2,175种,分别占中国种子植物区系的3.3%和8.0%。中国藤本植物区系热带成分显著,热带分布科和属分别占总科数或总属数(不含世界广布科属)的87.9%和79.2%;有14个含藤属为中国所特有,但没有特有含藤科。中国藤本植物最主要的攀援方式是缠绕类,占藤本植物总数的56.7%;其次为蔓生类和卷须类,分别占22.1%和17.0%;吸附类藤本种类最少,只占4.2%。     

Biomass allocation between extension- and leaf display-oriented shoots in relation to habitat differentiation among five deciduous liana species in a Japanese cool-temperate forest

Liana species have a variety of habitat preferences. Although morphological traits connected to resource acquisition may vary by habitat preference, few studies have investigated such associations in lianas. In previous work on temperate lianas, we observed (1) free standing leafy shoots and (2) climbing shoots that clung to host plants; we examined relationships between habitat preference and shoot production patterns in five liana species. Among the five species, two were more frequent at the forest edges (forest-edge species), and two were more common within the forests (forest-interior species). The proportion of climbing shoots in current-year shoot mass of young plants (3–8 m in height) was greater in the forest-edge species (45–60%) than in the forest-interior species (6–30%). In consequence, there was a greater leaf mass ratio in the total current-year shoots of forest-interior species. This, combined with a greater specific leaf area, endows forest-interior species with a leaf area per unit shoot mass double that of forest-edge species. Forest-edge species had longer individual climbing shoots whose length per unit stem mass was smaller than in forest-interior lianas. Extension efficiency, measured as the sum of the climbing stem length per unit current-year shoot mass, was thus similar between forest-edge and interior species. In conclusion, liana shoot production patterns were related to species habitat preferences. A trade-off between current potential productivity (leaves) and the ability to search for hosts and/or well-lit environments (climbing stems) may underpin these relationships.     

‘Hemiepiphyte’: a confusing term and its history

Background and Scope

Over more than 120 years of scientific study since Schimper''s seminal work, the recognized categories of structurally dependent plants have changed several times. Currently, ignoring parasitic mistletoes, it is usual to distinguish four functional groups: (1) true epiphytes; (2) primary hemiepiphytes; (3) secondary hemiepiphytes; and (4) climbing plants, i.e. lianas and vines. In this Viewpoint, it is argued that the term secondary hemiepiphytes (SHs) is misleading, that its definition is hard to impossible to apply in the field and, possibly causally related to this conceptual problem, that the use of this category in field studies is inconsistent, which now hampers interpretation and generalization.

Conclusions

Categories will frequently fail to capture gradual biological variation, but terms and concepts should be as unambiguous as possible to facilitate productive communication. A detailed analysis of the conceptual problems associated with the term SH and its application in scientific studies clearly shows that this goal is not fulfilled in this case. Consequently, the use of SH should be abandoned. An alternative scheme to categorize structurally dependent flora is suggested.     

Distribution and abundance of vines along the light gradient in a southern temperate rain forest

Question: Are vines light‐demanding species? Location: Temperate evergreen rain forest of southern Chile (40°39′S, 72°11′W). Methods: In 45 plots of 25 m² distributed in treefall canopy gaps, secondary forest stands and old‐growth forest (15 plots per light environment), all climbing and non‐supported vines were counted and identified to species level, and canopy openness was quantified using hemispherical photographs. Vine abundance and diversity (species richness and Simpson's index) were compared in the three light environments and similarity between vine communities was estimated using Jaccard's similarity coefficient. We also determined the relationship between light niche breadth and local dominance at the species level. Results: In total there were 2510 vine individuals of 14 species. Canopy openness was significantly different in the three light environments. Species richness, diversity, community composition and density of vines were similar in treefall gaps, secondary and old‐growth forest. Of the seven more common vine species, which accounted for 91% of all vines, three had even distribution, two were more abundant in the shaded understorey, and two had higher density in well‐lit sites. Local dominance of vine species and niche breadth were not significantly associated. Conclusions: Our study in a temperate rain forest questions the widespread notion of vines as pioneer‐like species, which may be a consequence of the abundance of some lianas in disturbed sites of tropical forests. Functional arguments are needed to justify a general hypothesis on light requirements of vines, which constitute a vast group of species.     

How the diversity,abundance, size and climbing mechanisms of woody lianas are related to biotic and abiotic factors in a subtropical secondary forest,Taiwan

Lianas are woody vines that play an important role in forest dynamics in tropical and subtropical areas. Their relationship to various biotic and abiotic conditions is, however, not yet wholly clear. We explored how the size, climbing mechanisms, diversity and abundance of woody lianas is related to host plant size, environmental factors and topography. Liana assemblages were examined in twenty 20 × 20 m plots in each of three topographic sites (valley, slope and ridge) in a subtropical secondary forest in southeastern Taiwan. The valley site had the highest abundance and species richness of lianas. The abiotic factors, soil pH and rock cover, were related to different topographic sites. Larger lianas were always found on larger host trees, while smaller lianas were found in smaller trees; no lianas with a DBH greater than 10 cm were found. Significantly more adhesive lianas were found on larger trees whereas twining and leaning-hook lianas were found in smaller trees. In conclusion, this study demonstrates that the species of liana is associated with the size and type of tree growing under different topographic conditions.     

The thermoregulatory limits of an Australian Passerine,the Silvereye (Zosterops lateralis)

(1) The thermal capabilities of Australian silvereyes (Zosterops lateralis, 11 g) were investigated both at low and high ambient temperatures (T_a) during the photophase and scotophase. (2). The peak metabolic rate (PMR) induced by helium–oxygen (79:21 %, He–O₂) exposure during the photophase was 15.64±1.55 mL O₂ g⁻¹ h⁻¹ at an effective lower survival limit T_a (T_pmr) of −39.7±6.1°C. (3). Above the thermoneutral zone (TNZ), metabolic rate, body temperature (T_b), and thermal conductance increased steeply, but they were able to withstand a T_a of 39°C. (4). Our study shows that silvereyes are able to tolerate an impressive range of T_a from about −42°C to at least +39°C and are able to produce enough heat to maintain a thermal difference between T_b and T_a of up to 80°C.     

广西弄岗五桠果叶木姜子群落木质藤本空间格局及其与树种间的关系

木质藤本是生物多样性的重要组成,木质藤本通过影响支持木进而影响群落的结构和功能,但在生物多样性丰富的北热带喀斯特森林中,木质藤本与支持木的关系鲜为人知。以喀斯特季节性雨林的五桠果叶木姜子（Litsea dilleniifolia）群落为研究对象,对木质藤本的密度、分布格局及其与主要树种的关系进行调查研究,分析木质藤本对树木的影响。结果显示：（1）五桠果叶木姜子群落内木质藤本平均密度为0.0913株/m²,木质藤本在0-20m空间尺度整体表现为聚集分布,且随着尺度增大,聚集强度逐渐减弱;不同径级木质藤本在不同尺度上的分布格局不同。（2）木质藤本对不同径级、不同种类、不同聚集强度的支持木选择表现以下体征：随着支持木径级增加,木质藤本攀附的比例和每木藤本数有增加趋势,且木质藤本胸径与支持木胸径呈极显著正相关;附藤率较高的支持木有紫葳科（Bignoniaceae）种类和东京桐（Deutzianthus tonkinensis）,单木附藤数量多的是南方紫金牛（Ardisia thyrsiflora）;物种的聚集强度与附藤率、附藤数量呈负相关。（3）木质藤本的密度与支持木死亡率关系不显著,而物种的附藤率与死亡率呈极显著负相关。以上结果表明,木质藤本密度在原生性喀斯特季节性雨林中并不高,且木质藤本对支持木具有选择性,但其对五桠果叶木姜子群落的死亡率并未产生显著影响。该研究可为喀斯特原生性季节性雨林的物种共存、极小植物种群保育提供理论依据,也可为石漠化区域的植被修复提供科学参考。     

Life History Traits of Lianas During Tropical Forest Succession

Tropical secondary forests form an important part of the landscape. Understanding functional traits of species that colonize at different points in succession can provide insight into community assembly. Although studies on functional traits during forest succession have focused on trees, lianas (woody vines) also contribute strongly to forest biomass, species richness, and dynamics. We examined life history traits of lianas in a forest chronosequence in Costa Rica to determine which traits vary consistently over succession. We conducted 0.1 ha vegetation inventories in 30 sites. To examine the establishment of young individuals, we only included small lianas (0.5–1.5 cm diameter at 1.3 m height). For each species, we identified seed size, dispersal mode, climbing mode, and whether or not the seedling is self‐supporting. We found a strong axis of variation determined by seed size and seedling growth habit, with early successional communities dominated by small‐seeded species with abiotic dispersal and climbing seedlings, while large‐seeded, animal‐dispersed species with free‐standing seedlings increased in abundance with stand age. Contrary to previous research and theory, we found a decrease in the abundance of stem twiners and no decrease in the abundance of tendril‐climbers during succession. Seed size appears to be a better indicator of liana successional stage than climbing mode. Liana life history traits change predictably over succession, particularly traits related to seedling establishment. Identifying whether these trait differences persist into the growth strategies of mature lianas is an important research goal, with potential ramifications for understanding the impact of lianas during tropical forest succession.     

Phytogeographical patterns of genera of endemic flora in relation to latitudinal and climatic gradients in China

This paper aims at detecting the relationships between phytogeographical patterns of genera of Chinese endemic seed plants and latitude or climatic factors. The landmass of China was divided into four latitudinal zones, each of c. 8°. Based on a total of 1664 indigenous genera of Chinese endemic seed plants which were grouped into fifteen geographical elements, belonging to three major categories (cosmopolitan, tropical and temperate) and which were absent or present in 28 provinces in China, we analyzed the phytogeographical patterns of genera of Chinese endemic seed plants and detected the relationships between them and main climatic factors. Our results showed that the proportion of tropical genera decreases with the increase in latitude; the proportion of temperate genera increases with the increase in latitude; and the proportion of cosmopolitan genera increased gradually increased gradually with latitude. There are a slow decrease in the proportion of tropical genera and slow increase in the proportion of temperate genera at latitudes 35°–40°. Alternatively, the tropical genera and the temperate genera have the same proportion at latitude c. 25°. These changes and issues about the different genera also appeared in main climate factors. In general, the genera present in a more northerly flora are a subset of the genera present in a more southerly flora. In summary, the large-scale patterns of phytogeography of endemic flora in China are strongly related to latitude, which covary with several climatic variables such as temperature.     

Infrared cameras overestimate skin temperature during rewarming from cold exposure

ObjectiveThe primary aim of this study was to assess the accuracy of an infrared camera and that of a skin thermistor, both commercially available. The study aimed to assess the agreement over a wide range of skin temperatures following cold exposure.MethodsFifty-two males placed their right hand in a thin plastic bag and immersed it in 8 °C water for 30 min whilst seated in an air temperature of 30 °C. Following hand immersion, participants removed the bag and rested their hand at heart level for 10 min. Index finger skin temperature (T_sk) was measured with a thermistor, affixed to the finger pad, and an infrared camera measured 1 cm distally to the thermistor. Agreement between the infrared camera and thermistor was assessed by mean difference (infrared camera minus thermistor) and 95% limits of agreement analysis, accounting for the repeated measures over time. The clinically significant threshold for T_sk differences was set at ±0.5 °C and limits of agreement ±1 °C.ResultsAs an average across all time points, the infrared camera recorded T_sk 1.80 (SD 1.16) °C warmer than the thermistor, with 95% limits of agreement ranging from −0.46 °C to 4.07 °C.ConclusionCollectively, the results show the infrared camera overestimated T_sk at every time point following local cooling. Further, measurement of finger T_sk from the infrared camera consistently fell outside the acceptable level of agreement (i.e. mean difference exceeding ±0.5 °C). Considering these results, infrared cameras may overestimate peripheral T_sk following cold exposure and clinicians and practitioners should, therefore, adjust their risk/withdrawal criteria accordingly.     

Estimation of intracellular pH in muscle of fishes from different thermal environments

A technique based on homogenisation of rapidly frozen tissue was used to investigate the regulation of intracellular pH (pH_i) in freshwater and marine fish from diverse environmental temperatures. The following species were held at ambient temperatures of ca. 1°C (Notothenia coriiceps; Antarctica), 5°C (Pleuronectes platessa, Myoxocephalus scorpius; North Sea), and 26°C (Oreochromis niloticus; African lakes). The effects of seasonal acclimatisation to 4, 11 and 18°C were also examined in rainbow trout in the winter, autumn and summer, respectively. Extracellular (whole blood) pH (pH_e) did not follow the constant relative alkalinity relationship, where pH⁺=pOH⁻ for any particular temperature, over a range of 1–26°C (overall δpH_e/δT=0.009±0.002 U °C⁻¹; P<0.001), apparently being regulated by ionic fluxes and ventilation. Intracellular pH (pH_i) was also regulated independently of pN(=0.5 pK water) in all species of fish examined. The inverse relationship between pH_i and environmental temperature gave an overall δpH_i/δT of −0.010±0.001 U °C⁻¹ (for both white and red muscle) and −0.004±0.003 U °C⁻¹ (cardiac muscle). However, between 1 and 11°C δpH_i/δT was much higher (P<0.001), −0.022±0.003 U °C⁻¹ (white muscle) and −0.022±0.004 U °C⁻¹ (red muscle). The possible adaptive roles for these different acid–base responses to environmental temperature variation among tissues and species, and the potential difficulties of estimating pH_i, are discussed.     

异军突起的藤本植物

对藤本植物(以热带为主)研究的动态与发展进行了综述,其中包括:(1)藤本植物的概念及重要性;(2)藤本植物区系和分布;(3)藤本植物的生物学特性;(4)藤本植物的生态学特性;(5)藤本在森林中的多度(密度)及种的丰富度;(6)藤本在空地上聚生的生态意义以及它们在森林演进过程中的消长;(7)藤本与树木的相互关系;(8)藤本对森林正面和负面的影响;(9)藤本的攀援方式类别及其竞争优势;(10)全球气候变化(CO₂浓度增高)促进藤本优势度增长并导致不良的生态后果。     

Large-scale phytogeographical patterns in East Asia in relation to latitudinal and climatic gradients

Aim This paper aims at determining how different floristic elements (e.g. cosmopolitan, tropical, and temperate) change with latitude and major climate factors, and how latitude affects the floristic relationships between East Asia and the other parts of the world. Location East Asia from the Arctic to tropical regions, an area crossing over 50° of latitudes and covering the eastern part of China, Korea, Japan and the eastern part of Russia. Methods East Asia is divided into forty‐five geographical regions. Based on the similarity of their world‐wide distributional patterns, a total of 2808 indigenous genera of seed plants found in East Asia were grouped into fourteen geographical elements, belonging to three major categories (cosmopolitan, tropical and temperate). The 50°‐long latitudinal gradient of East Asia was divided into five latitudinal zones, each of c. 10°. Phytogeographical relationships of East Asia to latitude and climatic variables were examined based on the forty‐five regional floras. Results Among all geographical and climatic variables considered, latitude showed the strongest relationship to phytogeographical composition. Tropical genera (with pantropical, amphi‐Pacific tropical, palaeotropical, tropical Asia–tropical Australia, tropical Asia–tropical Africa and tropical Asia geographical elements combined) accounted for c. 80% of the total genera at latitude 20°N and for c. 0% at latitude 55–60°N. In contrast, temperate genera (including holarctic, eastern Asia–North America, temperate Eurasia, temperate Asia, Mediterranean, western Asia to central Asia, central Asia and eastern Asia geographical elements) accounted for 15.5% in the southernmost latitude and for 80% at 55–60°N, from where northward the percentage tended to level off. The proportion of cosmopolitan genera increased gradually with latitude from 5% at the southernmost latitude to 21% at 55–60°N, where it levelled off northward. In general, the genera present in a more northerly flora are a subset of the genera present in a more southerly flora. Main conclusions The large‐scale patterns of phytogeography in East Asia are strongly related to latitude, which covaries with several climatic variables such as temperature. Evolutionary processes such as the adaptation of plants to cold climates and current and past land connections are likely responsible for the observed latitudinal patterns.     

Conformational variability of Gly-Gly segments in peptides: A comparison of the crystal structures of an acyclic pentapeptide and an octapeptide

The crystal structure of an acyclic pentapeptide, Boc-Gly-Gly-Leu-Aib-Val-OMe, reveals an extended conformation for the Gly-Gly segment, in contrast to the helical conformation determined earlier in the octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe [I. L. Karle, A. Banerjee, S. Bhattacharjya, and P. Balaram [1996] Biopolymers, Vol. 38, pp. 515–526). The pentapeptide crystallizes in space group P2₁ with one molecule in the asymmetric unit. The cell parameters are: a = 10.979(2) Å, b = 9.625(2) Å, c = 14.141(2) Å, and β = 96.93(1)°, R = 6.7% for 2501 reflections (I > 3σ(I)). The Gly-Gly segment is extended (ϕ₁ = −92°, ψ₁ = −133°, ϕ₂ = 140°, ψ₂ = 170°), while the Leu-Aib segment adopts a type II β-turn conformation (ϕ₃ = −61°, ψ₃ = 130°, ϕ₄ = 71°, ψ₄ = 6°). The observed conformation for the pentapeptide permits rationalization of a structural transition observed for the octapeptide in solution. An analysis of Gly-Gly segments in peptide crystal structures shows a preference for either β-turn or extended conformations. © 1997 John Wiley & Sons, Inc.     

陕西种子植物区系地理初步研究

陕西约有种子植物３９０７种,隶属于１７７科１１１５属,其中热带属３２８属（２９４４％）,温带属６４５属（５８１１％）,中国特有属５３属（４７５％）。区系地理成分分析表明,北温带分布属是其植物区系的核心,反映出区系的温带性质。然而这些温带区系成分并非起源于北方,而是亚热带山区起源,是华夏植物区系的北向延伸,其与亚热带和热带植物区系成分有着共同的起源,是华夏植物区系的组成部分。由于特殊的地理位置,决定了其成为多种地理成分的汇集之地,并表现出由亚热带向温带过渡的区系特点。此外区系中单、少种科、属及古特有属相对丰富,体现出区系的古老性。