浑善达克沙地几种优势植物的生态适应

浑善达克沙地是我国北方干旱半干旱区的主要沙地和严重荒漠化地区之一。同时也是我国内陆沙尘的主要源区之一。研究当地植物对沙地环境的适应方式有助于当地的荒漠化治理，加快生态环境恢复。本文应用（温室和野外）实验生态学方法研究了沙地植物对水分、沙埋和养分异质性环境的生态适应对策。 浑善达克沙地属于半干旱区域。在一次降雨过后，适合植物生长的湿沙层逐渐下降，或者说不适合植物生长的干沙层逐渐加厚。为了能够有效地从沙层中获得水分，植物的根系的伸长的速度必须大于湿沙层下降的速度。因此，当地分布的植物的根系则应该具有相应的形态、生长和生物量投资方面的可塑性。羊柴（Hedysarum laeve Maxim. (Leguminosae) ）是当地的主要半灌木和固沙植物。我们研究了羊柴幼苗对不同土壤含水量和不同模拟降雨量的反应格局，以及移动沙丘生长季节的土壤含水量变动规律。发现，大于3％土壤含水量适合羊柴幼苗生长。最适土壤含水量为12%－20% 。在生长季节早期，羊柴幼苗比较容易在沙丘上定居。如果没有充分的后续降雨的话，萌发后的幼苗在沙丘顶部、落沙坡中部和后部定居比较困难。降雨量越大，根系越深、总根长越大、根系直径越大、侧根越多、根冠比越低。 在干旱半干旱区域的沙地，种子萌发的时间和地点对于植物的定居和存活具有关键作用。通过温室实验，研究了小叶锦鸡儿和羊柴的种子萌发和出苗对不同深度的沙埋的反应，及其与种子大小的关联。结果表明，小叶锦鸡儿和羊柴的种子萌发和出苗对浑善达克沙地的自然生境表现出相似的生态适应。这两个种的种子萌发的适宜温度为10-15ºC, 这是当地春季的平均温度。由于这两个种的种子萌发是光敏感的，所以它们的种子萌发受土壤含水量和光照强度二者之间的平衡调节。2 cm 的较浅沙埋最有利于种子萌发和出苗。种子埋得越深，种子的萌发率和出苗率越低，更多的种子受胁迫休眠保存在土壤中作为种子库。不同大小的种子的不同萌发能力也是一种重要的生态适应，这可以调节种子在合适的时间和合适的沙埋深度萌发和出苗。 冰草（Agropyron cristatum (L.) Gaertn）是浑善达克沙地植物群落中占优势的多年生根茎草本植物之一。种子在合适的地点和时间萌发以及幼苗在合适的地点和时间生长，对于冰草在沙地环境条件下生存和分布具有重要意义。本文研究了浑善达克沙地4-10月份土壤含水量变动情况和冰草种子萌发、出苗和幼苗生长对土壤含水量的响应。结果表明，4月下旬至5月上中旬的土壤含水量对冰草种子萌发、出苗和定居极为关键。控制条件下，冰草种子萌发的最适土壤含水量是12%-20%，出苗以及幼苗生长的最适土壤含水量是12%-16%。当土壤含水量低于3%，冰草种子不能萌发，土壤含水量低于6%时，幼苗不能出土和定居。当土壤含水量达到16%时，冰草幼苗生物量有所下降。在6%-8%的土壤含水量条件下，植株将更多的生物量投资于根的生长。 本文对浑善达克沙地低湿滩地、滩地-风沙沉积过渡区到风沙沉积区的赖草（Leymus secalinus （Georgi） Tzvel.）分株数、地上生物量、土壤水分和养分异质性进行了研究。结果表明，从低湿滩地、滩地-风沙沉积过渡区到风沙沉积区，随着土壤养分的降低，赖草分株数和地上生物量反而增加。赖草的分株数在三种生境中都存在空间自相关。并且，从低湿滩地、过渡区到风沙沉积区空间自相关的变程逐渐增加。地上生物量同样存在空间自相关，但变程以过渡区最大，风沙沉积区最低。土壤水分仅仅在风沙沉积区存在空间自相关。在三种生境条件下，土壤全氮和有机质的空间分布格局相似，都在低湿滩地和过渡区存在空间自相关且变程相似。在风沙沉积区不存在空间自相关。赖草的空间分布格局在低湿滩地为偏离随机适度聚集的分布格局，在过渡区近似于聚居分布，而在风沙沉积区为均匀分布格局。 豆科锦鸡儿属（Caragana ）植物因其可以生物固氮而在草原生态系统当中具有特殊的地位。定量分析小叶锦鸡儿（Caragana microphylla ）灌丛在浑善达克沙地不同生境条件下的分布格局，有助于理解植被与土壤养分循环之间的关系和合理制定退化沙地的恢复对策。本文采用地统计学中的半方差分析和分形分析两种方法研究了浑善达克沙地小叶锦鸡儿灌丛的空间分布格局，分析了不同生境中小叶锦鸡儿灌丛的植被、土壤水分和养分间的相关性。结果表明（1）小叶锦鸡儿灌丛在三种生境条件下（滩地、固定沙丘和半固定沙丘）的盖度、土壤有机质和全氮的空间分布符合球状模型，空间自相关显著;（2）土壤pH值在滩地和固定沙丘的空间分布符合球状模型且空间自相关显著，但在半固定沙丘空间自相关不显著;（3）土壤水分在三种生境中的空间分布都符合线性模型，空间自相关显著。（4）植被的变异尺度（变程）小于各个土壤要素的变异尺度。植被（小叶锦鸡儿灌丛）的分布和形成过程决定了土壤养分的分布和形成过程。当地的豆科植物在养分“沃岛”现象的形成中起了重要作用，合理的利用和布局当地的豆科植物，可以更加有效地补充草地生态系统的养分，从而有利于加快当地生态系统的恢复进程。

转基因油菜和野芥菜杂交种的适合度

转基因植物与野生亲缘种间的基因流动是目前生物安全的研究热点。甘蓝型油菜（Brassica napus 以下简称油菜）及其亲缘种是基因流研究中的模式植物体系，油菜的亲缘种之一野芥菜(B. juncea)在中国分布广泛，是常见的农田杂草。本文以转基因抗虫油菜和野芥菜为研究材料，分别用综合适合度(基于生长和生殖)和适合度(仅基于种子产量)的指标来评估其杂交种在模拟农田情况下的适合度，揭示转基因在自然环境中的命运，以期为中国的油菜基因流的管理和控制提供参考。主要结果如下： 由于杂种优势和亲本效应的影响，转基因杂交种在不同的种植季节的生长与长势较好的亲本相近。因而转基因杂交种的综合适合度介于双亲之间，或与表现较好的亲本相似。因结实较差，从种子产量上来看，转基因杂交种的适合度较低。杂交种的后代因母本效应保留了一定的休眠特性，这有助于杂交种在种子库中持续存在。野芥菜和杂交种秋播时在冬季覆大棚条件下的适合度较高，在全球变暖的情况下，野芥菜和杂交种有可能在原先较冷不适宜的地区生长，从而促进转基因的散布。 杂交实验表明，转基因花粉与野芥菜的亲和性略高于非转基因花粉，但不显著；在两种花粉发生竞争时，转基因花粉的亲和性显著较高。混合花粉授粉的结实率高于单种花粉的结实率。可见在转基因花粉在授粉阶段不存在适合度代价。同时两季秋播田间实验表明，转基因油菜与非转基因油菜的适合度没有明显差异，即在植株的生长结实阶段，当没有竞争和虫害选择压力时，转基因没有适合度代价。也证明转基因散布的潜在可能性较大。此外，转基因杂交种的开花量很大，而回交实验中转基因杂交种花粉的育性高于胚珠的育性。转基因有可能通过持续的回交逃逸。 油菜的种子较大，野菜芥的种子较小，转基因油菜与野芥菜的杂交种基本都是小种子，其种子直径低于双亲。种子大小影响了发芽率、出苗率和营养生长期。小种子出苗率和发芽率较低，营养生长期较长。在没有竞争的条件下，春播实验中，种子大小对植物的适合度及综合适合度没有影响。秋播实验中种子大小对除转基因油菜外的所有植物基因型的综合适合度有显著影响。但对于依据种子产量计算的适合度指标来说，种子大小仅对野芥菜有影响，而对其它基因型影响不大。竞争扩大了种子大小之间生长表现的差异。竞争条件下，不同种子级别间的生长变异系数大于无竞争的情况。 总之，转基因花粉较强的竞争能力和其与野芥菜的亲和性使转基因杂交种的产生成为可能。来自母本的休眠特性有助于杂种种子在种子库中存在并在条件适宜时萌发、开花，有助于转基因的进一步扩散。转基因杂交种具有较高的综合适合度，虽然结实率很低，但其开花量比较大，可能会产生大量可育的花粉，在与野生亲本的持续回交过程中，转基因有可能逃逸。同时，转基因杂交种的种子级别偏小有可能会加剧这种逃逸。

岷江干旱河谷三种蔷薇植物繁殖更新研究

繁殖更新是植物生活史的重要阶段，在退化生态系统中，植物繁殖更新能力往往较差，是植被恢复的限制环节，因而也成为恢复研究重点和核心。本研究选择岷江干旱河谷广泛分布的三种蔷薇：多苞蔷薇（R. multibracteata）、黄蔷薇（R. hugonis）和川滇蔷薇（R. soulieana）为研究对象，通过野外调查，在查明其生长、繁殖更新状况的基础上，采用控制和模拟实验，对种子和幼苗阶段进行了深入研究，综合分析更新潜力，并提出相对应的促进更新和植被恢复措施。主要结论如下： 1）三种蔷薇在岷江干旱河谷广泛分布，生长和繁殖状况良好，结实量大。各生长指标：株高、基径和冠幅，繁殖指标：结实数量、重量和单果重量都具有显著的空间差异性。基径对多苞蔷薇结实量影响最大；而冠幅对黄蔷薇结实量影响最大。海拔和纬度是对蔷薇生长和繁殖影响最大的环境因素，随着海拔和纬度的升高，植株生长更高大，结实量增加；坡度和坡向对其生长和繁殖也有一定影响，随着坡度 和坡向增加，蔷薇生长和结实受到抑制。 2）三种蔷薇在岷江干旱河谷更新现状不佳, 但更新潜力大。活力种子比率低，动物取食以及两年生幼苗的大量死亡是蔷薇更新的主要限制因素。多苞蔷薇和黄蔷薇的结实率低，川滇蔷薇较高。三种蔷薇种子产量大，但种子质量较差，更新具有充足的种源。三种蔷薇都能形成持久种子库，种子库中种子总量大，但有效种子少，黄蔷薇被动物啃食的比例很高，多苞蔷薇和川滇蔷薇也有一部分种子受到动物破坏。三种蔷薇幼苗库组成特征表现为，当年生幼苗所占比例很高，年龄较大幼苗所占比例小。 3）三种蔷薇都具有不同程度休眠，未经处理种子的发芽率极低。黄蔷薇休眠程度最深，为深度生理休眠；多苞蔷薇为中度生理休眠；川滇蔷薇为非深度生理休眠。三种蔷薇种子在形态上发育成熟，种皮具有透水性。蔷薇果果肉和瘦果中含有抑制物质，其浸泡液抑制了油菜种子萌发，果肉抑制作用更强，果肉和瘦果浸泡液的抑制程度分别为：川滇蔷薇>黄蔷薇>多苞蔷薇。切割和硫酸腐蚀提高了川滇蔷薇种子的发芽能力，而对多苞蔷薇和黄蔷薇没有影响。完全去除瘦果果皮和种皮提高了多苞蔷薇种子发芽率，但对黄蔷薇没有影响。赤霉素和烟水对蔷薇种子萌发没有促进作用。三种蔷薇打破休眠所需低温层积时间分别为：黄蔷薇>多苞蔷薇>川滇蔷薇。对于多苞蔷薇和川滇蔷薇，层积前对种子进行硫酸腐蚀或暖温层积能缩短低温层积时间，提高发芽率。对于多苞蔷薇，变温层积中暖温层积和低温层积具有一定的负补性，即延长暖温层积可以缩短种子萌发对低温层积的需要。 4）多苞蔷薇种子形态特征和种子休眠与萌发在不同海拔梯度间存在较大差异。种子采集时间、采集季节和干藏影响多苞蔷薇和川滇蔷薇的种子休眠。多苞蔷薇果实大小、种子大小和千粒重、种皮厚度随海拔升高而增加，而种子饱满率和活力随海拔升高而降低，种子休眠程度也随海拔升高而增加。种皮厚度与种子大小、千粒重成正相关关系，硫酸腐蚀后的种子经过不同时间的低温层积后，种子发芽率与种皮厚度、种子大小、千粒重、海拔成正相关关系。2006 年采集川滇蔷薇和多苞蔷薇种子休眠程度较2005 年低。种子休眠随种子年龄增加而减弱。高温和干旱能减轻多苞蔷薇和川滇蔷薇种子休眠。 5）三种蔷薇的生长和生物量积累在干旱胁迫条件下受到抑制，而生物量分配、叶片形态特征和水分利用特征等都发生了变化。三种蔷薇的根、茎、叶各器官生物量以及总生物量等在干旱胁迫下明显减小，叶片脱落数量增加。在干旱胁迫条件下，较多的生物量分配到地下部分，从而这使R/S 明显增加。比叶面积（SLA）和冠层面积比（LAR）对干旱胁迫的反应不敏感，仅有部分物种在干旱胁迫条件下发生了变化，并且其变化特点在不同年龄幼苗之间有一定差异。干旱胁迫对WUE 的影响在不同物种间存在差异。多苞蔷薇和黄蔷薇的WUE 随着干旱胁迫的增加而增大， 而川滇蔷薇的WUE 则随干旱胁迫增加而减小。在干旱胁迫条件下，多苞蔷薇和黄蔷薇叶片脱落量和生物量减小幅度较川滇蔷薇大，表明其抗旱能力较强。在干旱胁迫条件，三种蔷薇两年生幼苗的生物量减小幅度较当年生幼苗小，表明两年生幼苗的抗旱能力更强。 6）两种植被恢复措施中，幼苗移栽比播种具有更好的植被恢复效果。播种后，蔷薇种子的发芽率较高，但出苗率都很低，即使出苗，幼苗也几乎在一月内全部死亡。 三种微生境条件下（灌木、半灌木和裸地），种子出苗和幼苗成活没有差异。移栽幼苗总体死亡率都比较低，小于20％。特别是两年生幼苗死亡率更低，小于2％。移栽后的幼苗生长状况良好，在整个生长季中，各生长指标不断增加。生境对幼苗的存活率没有显著影响，但对于幼苗的生长和生物量积累有一定影响，裸地更有利于幼苗生长和生物量积累。与当年生幼苗相比，两年生幼苗具有更高的成活率。总之，三种蔷薇在干旱河谷分布广泛、生长繁殖状况良好，结实量大，具有丰富种源，繁殖更新潜力大，但繁殖更新状况不佳；种子散布后动物对种子的取食、种子的深度休眠过程、种子出苗以及当年生幼苗的存活和定居是更新的主要限制环节。水分是影响结实、种子休眠解除和萌发，幼苗存活和定居的最主要的限制因素。在植被恢复中，应在种子成熟季节大量采集种子，在室内打破休眠后进行人工播种，培育两年生幼苗，通过幼苗移栽方式进行植被恢复。川滇蔷薇应栽种在相对湿润的过渡区，而多苞蔷薇和黄蔷薇可以应用于核心区植被恢复。 Regeneration is an important phase in plant life cycle. It has been a key component of ecological restoration in degradation ecosystem in which plants commonly has poor regeneration. In this paper, we investigated the natural growth, propagation and regeneration status of native three rose species, Rosa multibracteata, R. hugonis and R. soulieana, and analysis the limitation in seed germination and seedling establishment stages. Advice on facilitating the use of these plants in restoration based on the results has been proposed. The results were as follows: 1) Three rose plants widely distributed in the dry valley of the Minjiang River, and made a good performance in growth and propagation. There were significant spatial differences in each growth parameter, such as ramet height, basal diameter, crown diameter and propagation parameters including hip number of a clump, hip mass of a clump and a hip mass. Basa diameter was the most important growth parameter influencing fruit number for R. multibracteata and crown diameter was for R. hugoni. Altitude and latitude had the greatest effect on the growth and propagation of rose plants among environmental conditions. Each parameter of growth and propagation increased with the increase of altitude and latitude. In addition, the increase of slope and aspect limited the growth and propagation. 2) Three rose plants had poor natural regeneration, but great regeneration potential. Low seed viability, predation and higher mortality of current year old seedlings were the limitation in regeneration. R. multibracteata and R. hugonis had higher fruiting rates than R. souliean. All three plants produced a great number of seeds, while their viability was poor. Three rose plants had persistent seed banks, with high total seed number but very low viable seed density. Predation was most severe in R. hugonis, and it also existed to some degree in R. multibracteata and R. soulieana. The seedling age-structure was characteristic of current-year seedlings predominating and few older seedlings were observed. 3) Three rose seeds were dormant and untreated seeds germinated with very low germination percentages. The rose seeds had morphological mature embryos, and achenes were permeable. Some inhabit substances existed in hips and achenes for the extracts of hips and achenes inhibited germination of Brassica campestris. The inhibition effect of the extracts of three rose hip and achenes was R. soulieana>R. hugonis>R. multibracteata. Mechanical and H2SO4 scarification increased R. soulieana germination but had no effect on germination of R. hugonis and R. multibracteata seeds. Full removal of pericarp and testa improved the germination of R. multibracteata but did not affect R. hugonis germination. GA3 and smoke water had no positive effect on rose seed germination. The periods of cold stratification required to released seed dormancy was R. hugonis > R. soulieana >R. multibracteata. H2SO4 scarification and warm stratification shortened cold stratification to release dormancy for R. soulieana and R. multibracteata. Warm stratification had complementary effect for cold stratification, i.e. the longer warm stratification seeds received, the shorter cold stratification were required to obtain the same germination percentage. Three rose seeds had different kinds of dormancy; R. hugonis has deep physiological dormancy, R. multibracteata with intermediate physiological dormancy and R. souliean non-deep physiological dormancy. 4）The seeds traits and dormancy of R. multibracteata showed significant difference across altitudes. Year and season of seed collection had significant effect on seed dormancy for both R. souliean and R. multibracteata. Hip size, seed size, seed weight, seed coat thickness and seed dormancy level increased with the increase of the altitude. There were positive relations between seed coat thickness with seed size and seed weight. Germination percentage of seeds treated with H2SO4 scarification following different periods of cold stratification showed positive relation with seed coat thickness, seed size, seed weight and altitude. Seeds of R. souliean and R. multibracteata collected in 2006 had low dormancy level than those collected in 2005. Seed dormancy decreased with increasing seeds age. High temperature and drought were associated with low dormancy level. 5) Seedling growth, the total dry mass and their components of seedlings were reduced, while leaf senescence accelerated under drought stress. More biomass allocation to root system resulted in higher R/S ratio under drought. Water-use efficiency (WUE) of R. multibracteata and R. hugonis increased, while it declined for R. soulieana under drought stress. R. soulieana seedlings had poor drought-resistance capacity it had more senescent leaves, and its reduction of biomass was stronger than two other rose plants under drought. The reduction degree of one year old seedlings under drought stress was slighter than that of current year seedlings. Therefore, one year old seedling was more drought-resistent compared to current year seedlings. 6）Planting seedlings may have better effect in comparison with direct seeding. Most seeds germinated after seeding, but seedling emergence was very low. More than 80 % seedlings from direct seeding died within a months after emergence. Seedling emergence and survival rate did not show difference among microhabitats. Mortality rates of seedlings artificially planted in microhabitats were general lower than 20 %, and the mortality rate of one year old seedlings was lower than 2 %. Each grow parameter including plant height, leaf number and branch number continually increased after planting. Microhabitat type had effect on the growth parameter and biomass production, but it did not influence the seedling survival. Bare land tended to facilitate seedling growth. One year old seedlings had higher survival rate than current year seedlings. In conculsion, the three rose had wide distribution in the dry valley of the Minjiang River. They produced many seeds and had tolerance to drought stress to some degree. But they had poor regeneration in habitats may be caused by predation, seed dormancy，and high mortality in current year seedlings. We recommend that rose plants should be utilized in restoration by planting two-year old seedlings in spring. A large quantity of seeds should be collected artificially in autumn, release seed dormancy in room, and then cultivate two-year old seedlings by seeding in particular container. R. soulieana seedling probably be planted in transition area, and R. multibracteata and R. hugonis can be used in core area of the dry valley of the Minjiang River.

贡嘎山植物小枝功能性状在不同生活型和不同海拔间的比较研究

植物功能生态学研究不仅提供了植物生理生态学与生态系统生态学的连接，还为植物种群生活史对策研究提供了材料。Westoby 等 (2002) 提出了利用植物功能性状变量的主导维度来确定和量化植物生活史的生态适应策略。在他们所提出四个主导维度中，叶大小－小枝大小是研究相对较少的一维；其内部各组分的关系、对环境的响应，以及与其它重要维度的关系，目前的理解非常有限。 本研究以贡嘎山不同海拔不同功能群物种为研究对象，采用种间比较和系统发生独立性比较等研究方法，系统研究了植物的功能特征及其相关性在不同生境及不同功能群间的差异，旨在分析不同功能群物种的叶大小－小枝大小的成本和收益。其研究结果将有助于我们理解植物生活史对策的进化，进而理解物种共存和维持物种多样性的机制。主要研究结果如下： 1. 叶大小－小枝大小关系 小枝茎横截面积与单叶面积和总叶面积均呈异速生长关系，即总叶面积和单叶面积的增加比茎横截面积的增加速度快。但是，总叶面积和叶片干重的增加却基本上与小枝茎干重的增加等速。系统发生独立性比较研究的结果与此相一致。表明，在某一给定的茎投入时，至少大叶大枝物种不比小叶小枝物种在支撑叶面积和叶片干重方面具有优势。同时，在某一给定的小枝茎投入时，常绿阔叶物种比落叶阔叶物种支撑更少的叶面积。在茎干重与总叶面积的关系中，落叶复叶物种比落叶单叶物种具有更高的y轴截距，表明复叶物种比单叶物种在展叶面积方面更有效。复叶物种与单叶物种相比，通常具有较大的叶大小和小枝大小。 2. 叶大小－叶数量关系 叶大小与数量间在不同的叶片习性、不同的叶片形态以及不同的生境类型的物种间均存在稳定的负的等速生长关系，且这种关系在系统发生独立性比较时依然成立。然而，在某一给定的出叶强度 (单位小枝的叶数量) 时，常绿阔叶物种比落叶物种具有更小的叶面积。而在给定体积基础上的出叶强度时，落叶复叶物种的叶面积显著大于落叶单叶物种，且复叶物种比单叶物种具有更大的叶大小和更小的出叶强度。但是，叶大小与数量间的关系在不同的海拔间并没有显著的差异。 3. 小枝大小－总叶面积关系 在不同的生活型或不同的生境下，小枝上总叶面积与茎干重和小枝干重均呈正的异速生长关系，且斜率显著小于1.0，表明小枝上总叶面积的增加都不能赶上小枝及茎大小的增加。这种“收益递减”表明随着小枝干重的增加，光截取的收益递减。此外，叶面积比 (总叶面积与小枝干重的比值) 与单叶干重呈显著负相关关系，系统发生独立性比较的结果与此相一致。根据以上结果，可以推测，大叶的物种在质量较好的生境中出现，而群落内部小枝茎的寿命较长的物种可以拥有较大的叶片。 4. 叶片色素浓度－LMA关系 随着海拔的升高，阔叶木本植物和草本植物的叶片色素浓度减少，叶绿素a/b和类胡萝卜素/叶绿素比值以及比叶重 (LMA) 增加。然而，在草本植物中的色素浓度、色素比值和LMA的变化比阔叶木本植物的更明显。同时，LMA与叶片色素浓度呈负相关关系，但是在落叶物种中的LMA对色素浓度的影响比常绿阔叶物种更强烈。总之，草本植物的叶片特征对海拔梯度的变化似乎比木本植物更敏感，LMA对叶片色素的保护作用在落叶物种中比在常绿阔叶物种显得更重要。这些结果表明不同生活型物种可能采取不同的保护机制来降低叶绿体器官的损伤和增加他们的碳获取能力。 Studies on plant functional ecology not only bridge plant eco-physiology and ecosystem functioning, but also enrich plant population biology. As pointed out by Westoby et al (2002), plant life history strategies can be identified and quantified by four leading dimensions of variations in plant functional traits, i.e., seed size/output, leaf mass per area and leaf life span, plant height, and leaf size-twig size. Compared to the other dimensions, the cost/benefit of the leaf size-twig size spectrum has scarcely been analyzed in relation to environmental gradients and life form types, and the adaptive significance of this spectrum is not fully understood. In the present study, the relationships between functional traits of plant twigs are determined for the species with different life forms along an altitudinal gradient of Gongga Mountain with both cross-species analysis and evolutionary divergence analysis. The primary objective of this study is to examine the cost/benefit of leaf size-twig size in plants. The study results are supposed to provide insights into the understanding of the mechanism of species coexistences. The results are shown in the following. 1. The relationship between leaf size and twig size Twig cross-sectional area allometrically scaled with both individual leaf area and total leaf area supported by the twigs. However, the increase in total lamina mass/area was generally proportional to the increase in stem mass. These correlations between trait variations were significant in both interspecies analysis and phylogenetically independent comparison (PIC) analysis, which indicated that thick-twigged/large-leaved species, at least, do not have an advantage in supporting leaf/lamina area and lamina mass for the same twig stem investment than thin-twigged/ small-leaved species. Meanwhile, the evergreen broad-leaved species supported a smaller leaf area for the same twig stem investment in terms of both cross-sectional area and stem mass than the deciduous species. The deciduous compound-leaved species have a higher y-intercept in the scaling relationship of twig stem mass versus total leaf area than the deciduous simple-leaved species, indicating that compound-leaved species were more efficient in displaying leaf area. The compound-leaved species were larger in both leaf size and twig size than their counterpart in the present study. 2. The relationship between leaf size and leaf number Significantly negative and isometric scaling relationships between leaf size and leafing intensity (leaf number per twig mass or volume) were found to be consistently conserved across species independent of leaf habit, leaf form and habitat type. The negative correlations between leaf size and leafing intensity were also observed across correlated evolutionary divergences. However, leaf area was smaller in the evergreen broad-leaved species at a given leafing intensity than in the deciduous species. The deciduous compound-leaved deciduous species were higher in leaf area than deciduous simple-laved species at a given volume-based leafing intensity. Moreover, the compound-leaved deciduous species were larger in leaf size but smaller in leafing intensity than their simple counterparts. No significant difference was found in the scaling relationships between altitudes. 3. The relationship between twig size and total leaf area Leaf area was found to scale positively and allometrically with both stem and twig mass (stem mass plus leaf mass) with slopes significantly smaller than 1.0, independent of life form and habitat type, indicating that the increase in total leaf area fails to keep pace with increasing twig size and stem size. This ‘diminishing returns’ suggests that the benefit of light intercept decreased with increasing twig mass. Moreover, the leaf area ratio (the ratio of total leaf area to stem or twig mass) correlated negatively with individual leaf mass. The results of PIC were consistent with the correlations. According to the results, it is speculated that large-leaved species may be favored when habitat is good and when stem longevity are long within community. 4. The relationship between leaf pigment concentrations and leaf mass per area With increasing altitude, the concentrations of pigments decreased, but the ratios of chlorophyll a/b and carotenoid/chlorophyll, and LMA increased, in both the broad-leaved woody species and herbaceous species groups. However, the changes in the pigment concentrations, ratios and LMA were more profound in the herbaceous species than in the woody species. In addition, pigment concentrations were negatively correlated with LMA in each life form type and in the pooled dataset. However, the LMA effect on leaf pigment concentrations was more profound in the deciduous species than in the evergreen braode-leaved species. In general, herbaceous species seemed more sensitive to the increasing altitude compared to woody species, and LMA seemed to be a more important mechanism for protecting leaf pigments in deciduous species than in evergreen broad-leaved species. These results suggested that the species with different life forms may employ different protective mechanisms to decrease the chloroplast apparatus damage and increase their carbon gain.

Size and shape evolution of self-assembled coherent InAs/GaAs quantum dots influenced by seed layer

The size and shape Evolution of self-assembled InAs quantum dots (QDs) influenced by 2.0-ML InAs seed layer has been systematically investigated for 2.0, 2.5, and 2.9-ML deposition on GaAs(1 0 0) substrate. Based on comparisons with the evolution of InAs islands on single layer samples at late growth stage, the bimodal size distribution of InAs islands at 2.5-ML InAs coverage and the formation of larger InAs quantum dots at 2.9-ML deposition have been observed on the second InAs layer. The further cross-sectional transmission electron microscopy measurement indicates the larger InAs QDs: at 2.9-ML deposition on the second layer are free of dislocation. In addition, the interpretations for the size and shape evolution of InAs/GaAs QDs on the second layer will be presented. (C) 2001 Elsevier Science B.V. All lights reserved.

Size and shape evolution of self-assembled coherent InAs/GaAs quantum dots influenced by seed layer

The size and shape Evolution of self-assembled InAs quantum dots (QDs) influenced by 2.0-ML InAs seed layer has been systematically investigated for 2.0, 2.5, and 2.9-ML deposition on GaAs(1 0 0) substrate. Based on comparisons with the evolution of InAs islands on single layer samples at late growth stage, the bimodal size distribution of InAs islands at 2.5-ML InAs coverage and the formation of larger InAs quantum dots at 2.9-ML deposition have been observed on the second InAs layer. The further cross-sectional transmission electron microscopy measurement indicates the larger InAs QDs: at 2.9-ML deposition on the second layer are free of dislocation. In addition, the interpretations for the size and shape evolution of InAs/GaAs QDs on the second layer will be presented. (C) 2001 Elsevier Science B.V. All lights reserved.

Effects of seed dot layer and thin GaAs spacer layer on the structure and optical properties of upper In(Ga)As quantum dots

The structure and optical properties of In(Ga)As with the introduction of InGaAlAs or InAlAs seed dot layers are investigated. The area density and size homogeneity of the upper InGaAs dots are efficiently improved by the introduction of a buried layer of high-density dots. Our explanation for the realization of high density and size homogeneity dots is presented. When the GaAs spacer layer is too thin to cover the seed dots, the upper dots exhibit some optical properties like those of a quantum well. By analyzing the growth dynamics, we refer to this kind of dot as an empty-core dot. (C) 2003 American Institute of Physics.

Structure and optical properties of upper In(Ga)As quantum dots on a different seed layer with a thin GaAs spacer layer

The structure and optical properties of In(Ga)As grown with the introduction of InGaAlAs or InAlAs seed dots layers are investigated. The area density and size homogeneity of the upper InGaAs dots are efficiently improved with the introduction of a layer of high-density buried dots. When the GaAs spacer layer is too thin to cover the seed dots, the upper dots exhibit the characterization of a quantum well. By analyzing the growth dynamics, we refer to it as an empty-core structure dot. (C) 2002 Elsevier Science B.V. All rights reserved.

Effects of seed layer on the realization of larger self-assembled coherent InAs/GaAs quantum dots

The size and shape evolution of self-assembled InAs quantum dots (QDs) influenced by 2.0 ML InAs seed layer has been systematically investigated for 2.0, 2.5, and 2.9 ML deposition on GaAs(100) substrate. Based on comparisons with the formation of large incoherent InAs islands on single-layer samples at late growth stage, the larger coherent InAs quantum dots at 2.9 ML deposition has been observed on the second InAs layer. A simple model analysis accounting for the surface strain distribution influenced by buried islands gives a stronger increment of critical QD diameter for dislocation nucleation on the second layer in comparison with the single-layer samples. Additionally, the inhibition of dislocation nucleation in InGaAs/GaAs large islands can also be explained by our theoretical results. (C) 2000 American Institute of Physics. [S0021-8979(00)08922-2].

Seed-Mediated Growth of Nearly Monodisperse Palladium Nanocubes with Controllable Sizes

Nearly monodisperse Pd nanocubes with controllable sizes were synthesized through a seed-mediated growth approach. By using Pd nanocubes of 22 nm in size as seeds, the morphology of the as-grown nanostructures was fixed as single-crystalline, which enabled us to rationally tune the size of Pd nanocubes. The formation mechanism of initial 22 nm nanocubes was also discussed. The size-dependent surface plasmon resonance properties of the as-synthesized Pd nanocubes were investigated. Compared with previous methods, the yield, monodispersity, perfection of the shape formation, and the range of size control of these nanocubes are all improved.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Seed-mediated growth of large, monodisperse core-shell gold-silver nanoparticles with Ag-like optical properties

Large, monodisperse core-shell Au-Ag nanoparticles with Ag-like optical properties have been prepared by the seeding growth method in micellar media.

Effects of effective population size on the F-2 growth and survival of bay scallop Argopecten irradians irradians (Lamarck)

In 2002, six cohorts of broodstock bay scallop Argopecten irradians irradians (Ne=1, 2, 10, 30, 50 and control) were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F-2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups (Ne=10, 30, 50, control), and there were no significant differences among the latter (P>0.05). At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group (P<0.05). These results indicated that the low effective population size (Ne), which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Furthermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.

Extraction of Nitraria tangutorum seed oil by supercritical carbon dioxide and determination of free fatty acids by HPLC/APC/IMS with fluorescence detection

The seed oil from Nitraria tangutorum samples was obtained by supercritical carbon dioxide extraction methods. The extraction parameters for this methodology, including pressure, temperature, particle size and extraction time, were optimized. The free fatty acids in the seed oil were separated with a pre-column derivation method and 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-p-toluenesulfonate (BDETS) as a labeling regent, followed by high-performance liquid chromatography (HPLC) with fluorescence detection. The target compounds were identified by mass spectrometry with atmospheric pressure chemical ionization (APCI in positive-ion mode). HPLC analysis shows that the main compositions of the seed oil samples were free fatty acids (FFAs) in high to low concentrations as follows: linoleic acid, oleic acid, hexadecanoic acid and octadecanoic acid. The assay detection limits (at signal-to-noise of 3:1) were 3.378-6.572 nmol/L. Excellent linear responses were observed, with correlation coefficients greater than 0.999. The facile BDETS derivatization coupled with mass spectrometry detection allowed the development of a highly sensitive method for analyzing free fatty acids in seed oil by supercritical CO2 extraction. The established method is highly efficient for seed oil extraction and extremely sensitive for fatty acid profile determination. (C) 2007 Elsevier B.V. All rights reserved.