Effects of different seed pretreatments on germination of ten Calligonum species

In order to determine the optimum seed pre??sowing treatments and patterns of germination,a greenhouse experiment was conducted to study the effects of abrasion,sulphuric acid,boiling water,cold stratification and seed exudate treatments on the germination of ten Calligonum species.The results showed that the response of seed germination to the different pretreatments was similar for all ten Calligonum species.The abrasion,sulphuric acid and cold stratification treatments significantly promoted overall germinability.Compared with the control,the exudate treatment significantly decreased the percent germination,hampered the rate of germination and bolstered dormancy for almost all species.The cold stratification treatment can break the dormancy of viable Calligonum seeds and increased the germination,but it has a little lethal effect on viable seeds probably as well as the boiling water treatments.The germinaton patterns performed significant difference between the pre-sowing treatments for all ten Calligonum species,and the speed and percent germination of the Calligonum species can be greatly increased by mechanical scarification or sulphuric acid treatments.The results showed that seeds of C.junceum have strong ability of germinating.

新疆天山中段北部空中花粉数量的时空变化及其气候与植被指示意义

空中花粉是植被类型、气候状况与大气环境质量的指示物之一。空中花粉雨的取样实验对化石花粉谱的解释和古植被的恢复具有指导意义，因此空中花粉分析成为第四纪孢粉学和古生态学研究的有效辅助手段。本研究在新疆天山中段北坡进行了短期的空中花粉监测（2001年7月~2006年7月），目的是获得局域性和区域性植被所散发的花粉类型及其数量信息，并探讨花粉数量的植被与气候指示意义、花粉传播以及受环境条件影响的程度，同时分析和检测花粉浓度受气候条件的影响情况。空中花粉的收集使用Cour-type捕捉器，分别在3个不同海拔梯度进行5年连续的空中花粉收集（夏秋季节每周一个样品，冬春季节每两周一个样品）。取样地点分别是新疆天山中段北部的天池气象观测站（43°53'58.38"N, 88°07'15.75"E , 海拔1942.5m）、中科院阜康荒漠生态系统定位站（44°17'27.41"N, 87°55'52.65"E, 海拔477m）和准噶尔盆地古尔班通古特沙漠南缘的北沙窝试验站(44°22'40.74"N, 87°55'9.74"E, 海拔443m），取样点的植被带跨度天山北坡的森林草原到低海拔的典型荒漠。 光学显微镜鉴定的空中花粉主要有43种类型（24科30属），而蕨类、苔藓与真菌孢子数量较少。孢粉类型多样性指数为2.45（Shannon Index）。显然，从样品中所鉴定的空中花粉种类与所观察的植物种类有很大的差距。花粉类型与数量在三个不同海拔梯度的取样点上也有明显差异。天池取样点的花粉类型较丰富，与天山北坡垂直带植被分布以及丰富的植被成分相对应，花粉的优势种类为雪岭云杉(Picea schrenkiana)、蒿属(Artemisia)、藜科(Chenopodiaceae)、柽柳科(Tamaricaceae)和麻黄属(Ephedra)，高代表性的外源荒漠花粉类型“削弱了”本地花粉类型的代表性;阜康与北沙窝取样点的花粉类型主要来自荒漠成分的藜科、蒿属、麻黄属、蒺藜科(Zygophyllaceae, 白刺属Nitraria为主）、柽柳科（柽柳属为主）、蓼科(Polygonaceae, 沙拐枣属Calligonum为主）等耐旱植物。花粉数量与植被数量并非简单的线性关系。空中和表土花粉的数量分析表明，藜科、蒿属、麻黄属花粉具有超代表性;雪岭云杉花粉的代表性适中;禾本科(Gramineae)、榆属(Ulmus)、白刺属、柽柳科、沙拐枣属花粉代表性较差。 5年平均花粉浓度大小依次是阜康（81.668 grains/100m3）>天池（51.726 grains/100m3）>北沙窝（45.7685 grains/100m3）。蒿属花粉的峰值出现在秋季，并且出现双峰现象（可能与不同蒿类花期分布不均有关），而其它木本和草本类植物花粉浓度的峰值为单峰，具有明显的季节性，春夏之交开花的桦木属、榆属等类型较为明显。藜科花粉的峰值出现在夏季，麻黄和柽柳的峰值出现在盛夏，桦木属、柳属Salix、雪岭云杉等花粉浓度峰值出现在初夏，与其花期物候相对应。木本植物花粉以雪岭云杉为主，其次为桦木属(Betula)、榆属、柳属、胡颓子科(Elaeagnaceae)花粉，柳属花粉百分比在三个取样点分配比较均匀，桦木属花粉在空间分布上差异明显，与植物分布数量相关。胡颓子科的花粉出现时间短，数量也较少。榆属花粉出现的季节性明显，代表性也较差。因此解释地层中出现类似的低代表性和高代表性的花粉类型时，需要注意其百分比数量的适当校正。木本植物花粉百分比随海拔高度变化成正比关系，对植被的指示性较好。雪岭云杉的年平均花粉浓度在天池取样点明显高于其它两个取样点，5年的平均花粉浓度和百分比与海拔高度呈正比。天池取样点的百分比最高为28.85%，平均为21.15%，而北沙窝与阜康两地5年平均百分比含量分别为0.69%和1.57%，这种时空变化规律与植被数量的关系密切。藜科花粉百分比在阜康和北沙窝取样点占绝对优势，5年的平均花粉浓度与海拔高度呈反比。蒿属花粉年平均浓度与海拔高度关系微弱（R2=0.04，p =0.46），而花粉百分比与海拔高度有显著的线性正比关系（R2=0.72，p<0.0001）。但在低海拔的两个取样点之间差异不明显。 年平均花粉百分比和花粉浓度随海拔梯度而变化，主要花粉类型的变化规律存在差异。暗针叶林雪岭云杉花粉的年平均百分比在低海拔的阜康和北沙窝地区低于3%，在盛花期的6月初，低海拔的取样点也未见超过5%，雪岭云杉花粉的传播在研究区范围内数量分布变化较大，再次表明该类型的花粉在原地沉积效率很高。空中花粉数量能够较好地指示主要的植被带，盛花期内50%以上的雪岭云杉花粉含量则指示了雪岭云杉森林植被带，而高含量的蒿属植物花粉指示了天山山前冲积平原上的蒿类荒漠，相反，高含量的藜科花粉代表了低海拔地区的荒漠。雪岭云杉花粉百分比与浓度均与海拔高度呈显著的线性正比关系，表明雪岭云杉花粉传播的局限性。主要的非木本植物藜科花粉的浓度与海拔高度成反比，蒿属则相反，表明藜科与蒿属花粉在研究区具有很好的植被与气候指示意义。 花粉绝对数量、百分比、浓度具有明显的年际变化，其原因与气候状况的变化有关，年平均花粉浓度、主要类型的花粉浓度与气候参数（降水量、平均温度、最高和最低温度、相对湿度等）的相关分析表明，降水量和湿度与花粉浓度呈负相关程度较高，与其它气候参数则呈显著的正相关。干旱指数、花粉比值、花粉百分比（AP，NAP）与七月份平均气温，年平均降水量的相关系数（Pearson correlation），Ar/Ch与七月平均温度在0.01水平上呈显著的正相关（R2=0.894）, 与年平均降水量在0.01水平上呈显著的负相关（R2=0.874）。AP花粉百分比与七月份平均温度呈显著的负相关（R2=0.71, p<0.0001），与年降水量呈正相关（R2=0.43, p=0.01），而NAP花粉正相反。利用短期监测的空中花粉雨数据计算得到的花粉比值以及干旱指数在研究区具有明确的指示意义，尤其是干旱指数、Ar/Ch、Ar/Ep，这些都可为表土花粉、植被与气候关系模型的建立提供重要的参考信息。 气候参数在很大程度上影响大气花粉的浓度，而风速和风向对空中花粉的传播、散布影响较大，花粉的来源与传播受风向和风速的控制。不同取样点的空中花粉数量差异受地形条件影响很明显，这种差异也可利用地形空气动力学特征的差异来解释，天池监测站因“逆坡”（upslope）的气流促进了低海拔的花粉流向高海拔传播。 研究区的空中花粉数量信息是研究表土花粉、植被和气候关系以及第四纪古生态学的重要基础。本研究提高了对研究区空中孢粉的类型及其传播规律的认识和理解，增加了解空中花粉受环境影响的主要因素及其影响程度，对地层孢粉类型鉴定和花粉数据的解释提出指导性建议，对本地区的古植被与古环境研究增加现代孢粉学的参考依据和信息，并可为建立区域性的现代孢粉－植被－气候关系模型提供可靠依据。 同时，本报告也讨论了存在问题和不足，并提出了今后工作的可能完善方案。

塔克拉玛干沙漠南缘四种荒漠植物的生态生理学特性研究

植被破坏是造成塔克拉玛干沙漠南缘地区沙漠化严重发生的原因之一。研究植物的水分生理特性将为其恢复重建提供科学依据。本文在对塔克拉玛干沙漠南缘的四种荒漠植物（胡杨Popul us euphratica Oliv. 怪柳 Tamarixramosissima Ledeb.沙拐枣Calligonum caput medusae Schrenk.和骆驼刺Alhagi sparsifolia Shap.）的生态生理学特性（清晨水势、水势日变化、P一V曲线、茎流量、蒸腾速率、光合速率及水分利用效率）进行系统野外试验研究的基础上，经分析归纳，得出如下结论：（1)四种植物的清晨水势排序为：骆驼刺＞沙拐枣＞胡杨＞怪柳。四种植物的水势日变化同其清晨水势有基本一致的趋势（2)四种植物平均光合速率的排序为：怪柳＞胡杨＞沙拐枣＞骆驼刺；平均水分利用效率的排序为：沙拐枣＞胡杨＞怪柳＞骆驼刺；(3)四种植物在低水势下保持膨压能力大小的排序为：怪柳＞胡杨＞骆驼刺＞沙拐枣。其应对水分胁迫的共同反应是在细胞出现质壁分离时，保持高的体内含水量；(4)胡杨和怪柳的水分状况与水分的传输距离呈负相关关系。在对地下水传输距离的适应方面怪柳比胡杨表现出更强的适应性。（5)灌溉对怪柳幼苗的生长有利，而过量灌溉对于沙拐枣幼苗的生长不利。(6)在植被生长期内，四种植物没有受到严重的水分胁迫。植物的根系达到地下水位处并利用地下水。维持地下水位的基本稳定，是保证植被恢复重建的重要前提。本研究以欧盟合作项目和中国科学院策勒沙漠研究站为依托，结合当地实际，符合国家需求，在研究的系统性和区域水平性上属于首次。

沙漠-绿洲过渡带四种多年生植物水分关系特征

沙漠 -绿洲过渡带地区植被的可持续性在防止绿洲沙漠化的过程中非常重要。对过渡带主要植物种骆驼刺 (Alhagisparsifolia Shap)、多枝柽柳 (Tamarix ramosissima L ebed.)、胡杨 (Populus euphratica Oliv.)和头状沙拐枣 (Calligonum caput-medusae Schrenk.)水分关系的研究表明 :4种植物的水分恢复状况良好 ,清晨水势一直较高 ,水分亏缺并不严重。渗透势和正午水势的降低幅度不大 ,变化比较平稳 ,更像是一种生长过程中的结果 ,植物的水分胁迫状况并不明显。 4种植物的水势和渗透势都高于典型的荒漠植物 ,属于中生植物的范围。水分参数的变化显示在同样的环境节律下 ,四种植物在水分生理的变化特征上有一致性。一直很高的 RWCp 值表明植物不能适应剧烈的水分损失和较低的水分含量 ,植物需要稳定充足的水分供应来适应塔克拉玛干极端气候条件下的生长环境。植物对环境胁迫也有各自不同的生理适应特点 ,胡杨的ΔΠ值大 ,能忍受较多的水分损失维持气孔的开放 ;骆驼刺的Ψp 值最高 ,水分亏缺的平衡与恢复效果明显 ;C4 植物头状沙拐枣能维持较高的水势和渗透势 ,而盐土植物多枝柽柳能忍受水势的很大降低。夏季一次性灌溉对骆驼刺、多枝柽柳和胡杨水分状况的改善基本没有影响 ,对头状沙拐枣有一定的帮助。植物

Compound specific stable isotopes, BIT, pollen and spores of Miocene to Pliocene sediments of ODP Hole 175-1085A

Pollen and stable carbon (d13C) and hydrogen (dD) isotope ratios of terrestrial plant wax from the South Atlantic sediment core, ODP Site 1085, is used to reconstruct Miocene to Pliocene changes of vegetation and rainfall regime of western southern Africa. Our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Ma ago. We emphasise the importance of declining precipitation during the expansion of C4 and CAM (mainly succulent) vegetation in South Africa. We suggest that the C4 plant expansion resulted from an increased equator-pole temperature gradient caused by the initiation of strong Atlantic Meridional Overturning Circulation following the shoaling of the Central American Seaway during the Late Miocene.

AMS radiocarbon dates and pollen analysis of ODP Hole 175-1078C

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

XRF scanning, pollen and spores of ODP Site 108-659

Pliocene vegetation dynamics and climate variability in West Africa have been investigated through pollen and XRF-scanning records obtained from sediment cores of ODP Site 659 (18°N, 21°W). The comparison between total pollen accumulation rates and Ti/Ca ratios, which is strongly correlated with the dust input at the site, showed elevated aeolian transport of pollen during dusty periods. Comparison of the pollen records of ODP Site 659 and the nearby Site 658 resulted in a robust reconstruction of West African vegetation change since the Late Pliocene. Between 3.6 and 3.0 Ma the savannah in West Africa differed in composition from its modern counterpart and was richer in Asteraceae, in particular of the Tribus Cichorieae. Between 3.24 and 3.20 Ma a stable wet period is inferred from the Fe/K ratios, which could stand for a narrower and better specified mid-Pliocene (mid-Piacenzian) warm time slice. The northward extension of woodland and savannah, albeit fluctuating, was generally greater in the Pliocene. NE trade wind vigour increased intermittently around 2.7 and 2.6 Ma, and more or less permanently since 2.5 Ma, as inferred from increased pollen concentrations of trade wind indicators (Ephedra, Artemisia, Pinus). Our findings link the NE trade wind development with the intensification of the Northern Hemisphere glaciations (iNHG). Prior to the iNHG, little or no systematic relation could be found between sea surface temperatures of the North Atlantic with aridity and dust in West Africa.

Palynology on sediment profile Tso Kar in Ladakh

Palynological investigation of a 410 cm long core section from Tso Kar (33°10'N, 78°E, 4527 m a.s.l.), an alpine lake situated in the arid Ladakh area of NW India at the limit of the present-day Indian summer monsoon, was performed in order to reconstruct post-glacial regional vegetation and climate dynamics. The area was covered with alpine desert vegetation from ca. 15.2 to 14 kyr BP (1 kyr=1000 cal. years), reflecting dry and cold conditions. High influx values of long-distance transported Pinus sylvestris type pollen suggest prevailing air flow from the west and northwest. The spread of alpine meadow communities and local aquatic vegetation is a weak sign of climate amelioration after ca. 14 kyr BP. Pollen data (e.g. influx values of Pinus roxburghii type and Quercus) suggest that this was due to a strengthening of the summer monsoon and the reduced activity of westerly winds. The further spread of Artemisia and species-rich meadows occurred in response to improved moisture conditions between ca. 12.9 and 12.5 kyr BP. The subsequent change towards drier desert-steppe vegetation likely indicates more frequent westerly disturbances and associated snowfalls, which favoured the persistence of alpine meadows on edaphically moist sites. The spread of Chenopodiaceae-dominated vegetation associated with an extremely weak monsoon occurred at ca. 12.2-11.8 kyr BP during the Younger Dryas interstadial. A major increase in humidity is inferred from the development of Artemisia-dominated steppe and wet alpine meadows with Gentianaceae after the late glacial/early Holocene transition in response to the strengthening of the summer monsoon. Monsoonal influence reached maximum activity in the Tso Kar region between ca. 10.9 and 9.2 kyr BP. The subsequent development of the alpine meadow, steppe and desert-steppe vegetation points to a moderate reduction in the moisture supply, which can be linked to the weaker summer monsoon and the accompanying enhancement of the winter westerly flow from ca. 9.2 to 4.8 kyr BP. The highest water levels of Tso Kar around 8 kyr BP probably reflect combined effect of both monsoonal and westerly influence in the region. An abrupt shift towards aridity in the Tso Kar region occurred after ca. 4.8 kyr BP, as evidenced by an expansion of Chenopodiaceae-dominated desert-steppe. Low pollen influx values registered ca. 2.8-1.3 kyr BP suggest scarce vegetation cover and unfavourable growing conditions likely associated with a further weakening of the Indian Monsoon.

Distribution of pollen and spores in sediments of ODP Hole 175-1078C

The distribution of pollen in marine sediments is used to record vegetation change on the continent. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in the marine surface sediments and the occurrence of the source plants on the adjacent continent. To investigate land-sea interactions during deglaciation, we compare proxies for continental (pollen assemblages) and marine conditions (alkenone-derived sea surface temperatures) of two high-resolution, radiocarbon-dated sedimentary records from the tropical southeast Atlantic. The southern site is located West of the Cunene River mouth; the northern site is located West of the Angolan Huambe Mountains. It is inferred that the vegetation in Angola developed from Afroalpine and open savannah during the last Glacial maximum (LGM) via Afromontane Podocarpus forest during Heinrich Event 1 (H1), to an early increase of lowland forest after 14.5 ka. The vegetation record indicates dry and cold conditions during the LGM, cool and wet conditions during H1 and a gradual rise in temperature starting well before the Younger Dryas (YD) period. Terrestrial and oceanic climate developments seem largely running parallel, in contrast to the situation ca. 5° further South, where marine and terrestrial developments diverge during the YD. The cool and wet conditions in tropical West Africa, South of the equator, during H1 suggest that low-latitude insolation variation is more important than the slowdown of the thermohaline circulation for the climate in tropical Africa.

Palynology of marine sediment cores from the West African coast

Seven sediment cores from the cruises of the "Meteor" and "Valdivia" were examined palynologically. The cores were retrieved from the lower continental slope in the area of between 33.5° N and 8° N, off the West African coast. Most of the cores contain sediments from the last Glacial and Interglacial period. In some cases, the Holocene sediments are missing. Some individual cores contain sediments also from earlier Glacial and Interglacial periods. The main reason for making this palynological study was to find out the differences between the vegetation of Glacial and Interglacial periods in those parts of West Africa which at present belong to the Mediterranean zone, the Sahara and the zones of the savannas and tropical forests. In today's Mediterranean vegetation zone at core 33.5° N, forests and deciduous forests in particular, are missing during Glacial conditions. Semi-deserts are found instead of these. In the early isotope stage 1, there is a very significant development of forests which contain evergreen oaks; this is the Mediterranean type of vegestation development. The Sahara type of vegetation development is shown in four cores from between 27° N and 19° N. The differences between Glacial and Interglacial periods are very small. It must be assumed therefore that in this latitudes, both Glacial and Interglacial conditions gave rise to desert generally. The results are in favour of a slightly more arid climate during Glacial and more humid one during Interglacial periods. The southern boundary of the Sahara and the adjacent savannas with grassland and tropical woods were situated more to the south during the Glacial periods than they were during the Interglacial ones. In front of today's savanna belt, it can be seen from the palynological results that there are considerable differences between the vegetation of Glacial and Interglacial periods. The woods are more important in Interglacial periods. During the Glacial periods these are replaced from north to south decreasingly by grassland (savanna and rainforest type of vegetation development). The southern limit of the Sahara during stage 2 was somewhat between 12° N and 8° N which is between 1.5 and 5 degrees in latitude further south than it i s today. Not only do these differences in climate and vegetation apply to the maximum of the last Glacial and for the Holocene, but they apparently apply also to the older Glacial and Interglacial periods, where they have been found in the profiles. The North African deset belt can be said to have expanded during Glacial times both towards the north and towards the south. All the available evidence of this study indicates that the grass land or the semi-desert of the Southern Europe cam einto connection with those of the N Africa; there could not have been any forest zone between them. The present study was also a good opportunity for investigating some of the basic marine palynological problems. The very well known overrepresentation of pollen grains of the genus Pinus in marine sediments can be traced as fa as 21° N. The present southern limit for the genus Pinus is on the Canaries and on the African continent as approximately 31° N. Highest values of Ephedra pollen grains even occur south of the main area of the present distribution of that genus. These does not seem to be any satisfactory explanation for this. In general, it would appear that the transport of pollen grains from the north is more important than transport from the south. The results so far, indicate strongly that further palynological studies are necessary. These should concentrate particularly on cores from between 33° N and 27° N as well as between 17° N and 10° N. It would also be useful to have a more detailed examination of sediments from the last Intergalcial period (substage 5 e). Absolute pollen counts and more general examination of surface samples would be desirable. Surface samples should be taken from the shelf down to the bottom of the continental slope in different latitudes.

Palynology of ODP Site 108-658

Ocean Drilling Program Site 658 at 21°N off northwest Africa has a high sedimentation rate and a high concentration of pollen grains and is thus very suitable for detailed pollen analysis. The time scale for the upper 100 m (the last 670 k.y.) of Site 658 is based on biostratigraphic data and isotope stratigraphy. The pollen record has been divided into 34 zones. These are classified into 7 zone types covering a range from very arid to rather humid conditions. The sequence shows a long-term climatic decline: strong glacial stages were found only after 480 k.y. and strong interglacial stages only before 280 k.y. The Site 658 record correlates well with a terrestrial sequence from northern Greece, although both records differ in their response to global climatic change. Spectral analysis shows a 100- and a 42-k.y. period in the curves of pollen brought in by the northwest trade winds and only a 42-k.y. period in the curves of pollen mostly transported by the African Easterly Jet. A 31-k.y. period is found in the curves for Ephedra and Chenopodiaceae-Amaranthaceae. In addition, Ephedra shows a 54-k.y. period.