间伐强度对黄桥林区辽东栎林结实规律的影响

为了阐明抚育间伐强度对辽东栎林结实规律的影响,以黄土高原南部黄龙山和桥山林区辽东栎中龄林为研究对象,对不同间伐强度(对照、10%、20%、30%)近自然经营抚育间伐5年后的林分密度与结实母树比例、平均单株结实与单位面积林分总结实量、种子在树冠上空间分布特征及种子特征等进行调查分析.结果表明: 辽东栎林结实母树的比例、平均单株结实量及发育种子比例均随着间伐强度的增大而增大,表现为30%>20%>10%>对照;而单位面积林分总结实量在20%强度间伐时达到最大,表现为20%>30%>对照>10%.从辽东栎种子在树冠上的空间分布来看,73.6%的种子集中分布于树冠上层,26.4%分布于下层.树冠阳面结实量占总结实量的65.8%,树冠阴面仅占34.2%,间伐强度对树冠下层、阴面结实量的提升幅度分别大于树冠上层和阳面.辽东栎种子的长径、短径及千粒重均随间伐强度的增大而增大,在30%间伐强度时达到最大.10%强度间伐对辽东栎林结实影响不显著,间伐强度达到20%时,才能显著提高辽东栎种子的数量和品质,继续提高间伐强度到30%时,并不能有效提高其结实,而其林分总结实量却下降.建议在对该林区进行抚育间伐时,应选择20%的间伐强度(保留郁闭度0.7),可有效提高辽东栎种群的结实量和品质.     

常绿阔叶树种栲树开花物候动态及花的空间配置

 基于定株观测和随机枝取样法,对浙江天童常绿阔叶林内栲树（Castanopsis fargesii）的开花物候动态及其雌花、雄花的空间配置进行了研究。结果表明：在栲树的生殖枝上,并非所有的芽都分化、萌发生成花序,栲树花芽的分化和发育集中在一级生殖枝上。生殖枝上花芽的分化与该枝的空间位置密切相关。栲树花期明显晚于春季的展叶期,与叶片生长时间重叠。盛花期集中于5月下旬,约持续8 d左右,属于同步发生的花期。栲树雄花序的数量明显高于雌花序,雄花序约占花序总数的77.88%,雌花序仅占22.12%。大量雄花和花粉的存在是保证雌花接受花粉和完成受精的基础。花序在植冠层中的空间配置明显不同：在同一植冠内,向阳面和背阴面生殖枝上芽萌发成花序的比率存在明显差异(p<0.01),阳面生殖枝上顶芽萌发成花序的比率高于阴面生殖枝的比率,并且,阳面的每个生殖枝上平均花序数和雄花数量均高于阴面生殖枝,花序的分化和发育与枝系的生长发育状况有密切关系。     

两种生境条件下西南桦的生殖构件及其空间格局

在广西靖西土石山生态交错区调查了西南桦(Betula alnoides)生殖植株的生长状况,并研究土山和石山两种生境条件下西南桦的生殖构件及其在冠层的分布格局.结果表明:石山西南桦开始开花结实的林木胸径明显小于土山;两种立地上西南桦植株的花芽、花序数以及雄花序比率与其胸径、树高均不显著相关(P>0.05);土山和石山的西南桦雄花序数随着总花序数的增加均呈对数曲线增长趋势,在生殖投资较小的情况下植株趋向于优先发育雄花序,而在生殖投资较大时主要增加雌花序的数量;西南桦生殖构件在两种生境间存在显著差异,石山植株的雄花芽数、每个雄发芽发育出的雄花序数均显著低于土山(P<0.05),雄花序少于雌花序的植株比例远高于土山,生殖枝比率亦显著低于土山(P<0.05);尽管石山雄花序、雌花序和总花序数量以及雄花序比率低于土山,其雌花序比率高于土山,但是由于两种立地上单株间变异幅度大,独立t检验表明其差异均未达到显著水平;两种立地上西南桦花序大多着生于树冠上、中层,且90%以上的生殖枝居于树冠外层.     

不同间伐强度对辽东栎林群落稳定性的影响

对黄土高原地区近自然经营间伐强度为13.4%(弱度间伐)和30.0%(强度间伐)的辽东栎林进行样地调查,并以未间伐林为对照,研究间伐后第5年建群种的更新潜力、林地生产力、土壤肥力和物种多样性;应用模糊数学中的隶属函数方法对辽东栎林群落稳定性进行评价.结果表明：与对照相比,弱度和强度间伐使辽东栎林地的更新潜力分别提高了14.2%和20.2%;立木蓄积量分别减少了9.0%和23.8%,但灌木生物量分别增加7.3%和12.2%,草本生物量分别增加10.5%和31.6%.间伐样地的土壤肥力和物种多样性指数均高于未间伐样地.辽东栎林群落稳定性表现为：强度间伐＞弱度间伐＞未间伐.近自然经营采伐强度30.0%更适合黄 土高原地区辽东栎次生林的抚育管理.     

辽东栎芽库统计:芽的命运

植物体是一个构件集合体,植物的枝系伸展可由芽库出生率、死亡率的统计学过程来分析。在东灵山地区,应用随机枝取样法调查了辽东栎芽的命运,并对其与枝长、叶数、果数等的关系进行了统计分析。结果表明：（1）辽东栎的芽或保持休眠状态,或死亡后脱落,或分化为营养枝、生殖枝（包括雄花枝、雄花序、雌花枝和两花枝）等;（2）不同生境中芽的命运不同,生活在林窗中的幼树上的芽分化为具有生殖功能的枝条的比例显著高于郁闭林中的幼树,而与成熟个体接近;（3）芽的命运还受其它因子的影响,如上层枝条上、或叶数多的长枝上的芽分化为生殖枝的可能性大于其它的芽,另外还发现结实枝的枝长、枝上叶数都明显高于非结实枝。     

辽东栎林内不同小生境下幼树植冠构型分析

以黄土高原黄龙山林区辽东栎林内3个小生境（林下、林隙、林缘）下辽东栎天然更新幼树为研究对象,采用典型抽样法对辽东栎幼树侧枝、叶片和树冠的空间分布状况以及生物量分配状况进行调查分析,探讨微生境与幼树植冠构型特征的关系,明确辽东栎幼树对不同小生境的适应策略,为栎林经营和林分结构优化提供理论依据。结果显示：（1）3种生境下辽东栎幼树构型发生了可塑性变化,林下幼树树冠层次比较单一,林隙与林缘的幼树树冠层次更加丰富。（2）由林下至林缘,幼树的树高、枝下高呈逐渐减小的趋势,而地径变化趋势与之相反;幼树的冠幅、树冠面积、树冠率呈先增加后减小的趋势,并且林下与林隙、林缘的差异显著;幼树的总体分枝率、逐步分枝率、枝径比呈先增加后减小的趋势。（3）3种生境下,幼树的一级枝的枝长、直径与倾角随着树高的增加而呈减小的趋势,但3种生境的差异不显著;林下一级枝主要分布在冠层中上部,而林隙与林缘一级枝主要分布在冠层中下、中上部。（4）由林下至林缘幼树叶长、叶宽、单叶面积和比叶面积逐渐降低,而单株叶数、叶总面积、叶面积指数呈先增大后减小趋势;与其他2种生境相比林下叶片分布趋于冠层上部。（5）幼树地上部分生物量中林下主干生物量占83%,枝和叶生物量只占17%;而林隙与林缘虽然各部位生物量有所差异但比例基本一致,其中主干占66%左右,枝和叶生物量占34%左右。研究表明,林隙生境下幼树的构型优于林缘和林下生境,在今后栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化提供有利条件。     

黄龙山林区不同郁闭度对辽东栎种群结构的影响

辽东栎是黄龙山林区主要的建群种,通过典型取样选择16块样地,对其年龄结构、静态生命表、存活曲线、高度级结构、冠幅结构的绘制,研究其在不同郁闭度(0.6、0.7、0.8、0.9)不同坡向(阴坡、阳坡)生境中变化规律。结果表明:辽东栎幼苗数量在郁闭度0.6、0.7、0.8、0.9样地中,分别占全部个体数量的57%、64%、36%、47%,从年龄结构、静态生命表、存活曲线均表明辽东栎幼苗在4个不同郁闭度中比例都是最大的,大树比例次之,幼树小树比例最少,幼树小树是辽东栎更新瓶颈阶段,辽东栎种群存活曲线均属于R.PearlⅢ型,在郁闭度0.7波动最小;从辽东栎种群的年龄结构、静态生命表、存活曲线、高度级结构、冠幅结构等指标综合表现中可以看出辽东栎种群在郁闭度0.7生境优于郁闭度0.6、0.8、0.9生境;辽东栎在阳坡的幼苗、幼树、小树、比例高于阴坡,而大树比例低于阴坡;除高度级a外,阳坡多集中在c、d、e高度级,阴坡高度级多集中在d、e、f;在阳坡冠幅级10以下均有分布,在阴坡冠幅多集中在冠幅级7以下;无论在阳坡还是阴坡,郁闭度0.7更适合辽东栎更新生长,可以作为西北地区抚育间伐的理想条件。     

黄土高原柴松群落优势乔木树种的竞争关系

采用Voronoi图确定竞争单元的方法,从树木胸径和冠幅角度对黄土高原柴松(Pinus tabulaefirmisf.shekanensis)群落的优势乔木树种——柴松和辽东栎(Quercus liaotungensis)的种内、种间竞争强度进行了定量分析。结果表明:1)柴松种群受到强烈的种间树冠竞争和种内的胸径竞争,在胸径10cm时受到来自种内种间的竞争压力最大,其结果对柴松的生长有显著影响;2)辽东栎种群在胸径5cm时受到更多来自种间林冠的竞争,当胸径为5~10cm时种内冠幅间的竞争强度超过种间,种间冠幅竞争强度与辽东栎的林木生长无显著相关,说明柴松不能对辽东栎产生强烈持续的树冠竞争;3)柴松、辽东栎种群竞争强度均随着对象木径阶的增大而减小,竞争强度(CI)与对象木胸径大小(D)服从幂函数(CI=ADB)关系。     

白桦的开花时间及生殖构件的数量与树龄和树冠层次的关系

白桦的初始开花结实年龄在不同生境、不同起源情况下是有很大差别的。在相同地生境下,实生苗比萌生苗的始花年龄晚６ａ以上,中生生境的林分始花期要早于湿生生境的林分,在同一年中花期的早晚因林龄而异。花序构件种群、生殖技构件种群以及生殖枝花序数量都与树龄直接相关。花序构件数量壮年期〉老龄期〉结实初期。在同一生殖个体上,构件数量雄花序为中层〉上层〉下层,雌花序数量为土层〉中层〉下层,每个生殖枝平均的花序构件数     

不同经营措施对黄龙山辽东栎林的影响

以黄龙山林区蔡家川林场的辽东栎群落为研究对象,以未采伐为对照,采取皆伐、间伐30%、间伐15%三种经营措施,在进行自然恢复6年后,对辽东栎林建群种径级结构、群落物种多样性、土壤养分水分状况进行了对比分析,以探讨不同经营措施对黄土高原南部辽东栎(Quercus liaotungensis)林群落多样性的影响.结果表明:不同经营措施实施后建群种径级结构、群落物种多样性、土壤养分水分等指标均与未采伐林地有差异;经过间伐30%的林地,建群种径级结构、群落物种多样性、土壤养分水分等指标均有显著增加;间伐15%林地上述指标均有增加,但不显著;皆伐后的林地相对未采伐林地,建群种径级结构、群落物种多样性、土壤养分水分等指标降低.间伐与皆伐措施后比较,间伐措施的林地建群种个体生长发育良好,林下有大量幼苗,林地物种多样性丰富,土壤养分水分相对优越;皆伐措施的辽东栎建群种个体发育不良,缺乏足够数量的幼苗,林分物种多样性、土壤水分养分相对较差.未来该地区辽东栎林经营管理中,应以近自然经营措施为主,尽量减少对灌草层破坏,完善群落复层结构;间伐强度拟定为30%,尽量间伐劣质木、病虫木,促进群落向异龄方向发展.     

Resource partitioning to male and female flowers of Spinacia oleracea L. in relation to whole-plant monocarpic senescence

Male plants of spinach (Spinacea oleracea L.) senesce following flowering. It has been suggested that nutrient drain by male flowers is insufficient to trigger senescence. The partitioning of radiolabelled photosynthate between vegetative and reproductive tissue was compared in male (staminate) versus female (pistillate) plants. After the start of flowering staminate plants senesce 3 weeks earlier than pistillate plants. Soon after the start of flowering, staminate plants allocated several times as much photosynthate to flowering structures as did pistillate plants. The buds of staminate flowers with developing pollen had the greatest draw of photosynthate. When the staminate plants begin to show senescence 68% of fixed C was allocated to the staminate reproductive structures. In the pistillate plants, export to the developing fruits and young flowers remained near 10% until mid-reproductive development, when it increased to 40%, declining to 27% as the plants started to senesce. These differences were also present on a sink-mass corrected basis. Flowers on staminate spinach plants develop faster than pistillate flowers and have a greater draw of photosynthate than do pistillate flowers and fruits, although for a shorter period. Pistillate plants also produce more leaf area within the inflorescence to sustain the developing fruits. The (14)C in the staminate flowers declined due to respiration, especially during pollen maturation; no such loss occurred in pistillate reproductive structures. The partitioning to the reproductive structures correlates with the greater production of floral versus vegetative tissue in staminate plants and their more rapid senescence. As at senescence the leaves still had adequate carbohydrate, the resources are clearly phloem-transported compounds other than carbohydrates. The extent of the resource redistribution to reproductive structures and away from the development of new vegetative sinks, starting very early in the reproductive phase, is sufficient to account for the triggering of senescence in the rest of the plant.     

Sex expression as affected by N6-benzylaminopurine in staminate inflorescence of Luffa cylindrica

The effect of N⁶-benzylaminopurine (BA) on the sex expressionof staminate inflorescences of Luffa cylindrica was investigated.Direct application of BA to the staminate inflorescence inducedbisexual and pistillate flowers and finally caused the inflorescenceto develop into a shoot that was similar to the main shoot.Such modification in a staminate inflorescence from the proximalto the distal nodes is usually in the order of staminate flowers,bisexual flowers, pistillate flowers and foliage leaves (shoot).Pinching of the main stem also caused the inflorescence to developinto a shoot in the absence of lateral shoots. BA-induced femalenesswas strengthened when the number of leaves remaining on theplant was increased. On the other hand, application of BA tothe shoot apex of the main stem starting at the 2-leaf stagesuppressed differentiation of the flower bud on the main stem. (Received December 22, 1979; )     

Reproductive structures of an extinct platanoid from the early Cretaceous (latest Albian) of eastern North America

Two new species of platanoid reproductive structure are described from the Bull Mountain locality in the Patapsco Formation (Potomac Group) of northeastern Maryland, USA. Pistillate inflorescences and infructescences (Platanocarpus elkneckensis sp. nov.) consist of flowers and fruits in sessile globose heads that are borne on an elongate axis. Individual pistillate flowers consist of five free carpels surrounded by prominent tepals. Staminate inflorescences, flowers and isolated stamens are assigned to Hamatia elkneckensis gen. et sp. nov. Staminate flowers are borne in a globose head with a small number of stamens (five?) per flower. Stamens consist of very short filaments, long anthers with strongly valvate dehiscence and an apically expanded connective. The connective expansion is frequently very well-developed, hook-like and extends down the ventral surface of the stamen. Anthers contain small, tricolporate, reticulate pollen. Association evidence, similarity of inflorescence structure and the occurrence of Hamatia-type pollen on flowers, carpels and fruits of Platanocarpus elkneckensis suggests that the staminate and pistillate material was produced by a single species of plant. The “Hamatia-plant” provides further evidence of pentamerous floral structure in mid-Cretaceous platanoids and documents the occurrence of unequivocal tricolporate pollen in the platanoid complex.     

Reproductive developmental complexity in the African oil palm (Elaeis guineensis, Arecaceae)

Species of the palm family (Arecaceae) are remarkably diverse in their inflorescence and floral morphologies, which make them a particularly interesting group for studies of reproductive development and its evolution. Using light and scanning electron microscopy, we describe inflorescence and flower development in the African oil palm Elaeis guineensis from the initiation of the inflorescence meristem to flower maturity. In mature palms, the inflorescence develops over 2-3 years and is characterized by individual stages within which differentiation may be either relatively slow, as in the case of early inflorescence meristem development, or rapid, as in the case of flower organogenesis. The female inflorescence bears floral triads composed of single pistillate flowers flanked by two abortive staminate flowers, whereas the male inflorescence contains single functional staminate flowers. This suggests a possible evolutionary movement from an ancestral hermaphrodite inflorescence form containing fully functional floral triads to the situation of temporal dioecy observed at present. Wild type flowers are compared to those bearing an epigenetic homeotic abnormality, known as mantled, involving an alteration of the identity of the organs in the fertile and sterile androecium.     

Early inflorescence and floral development in Cocos nucifera L. (Arecaceae: Arecoideae)

Palms are generally characterized by a large structure with a massive crown that creates difficulties in anatomical studies. The flowering behaviour of palm species may be a useful indicator of phylogenetic relationships and therefore evolutionary events. This paper presents a detailed histological study of reproductive development in coconut (Cocos nucifera L.), from initiation up to maturation of staminate and pistillate flowers. Reproductive development in coconut consists of a sequence of individual events that span more than two years. Floral morphogenesis is the longest event, taking about one year, while sex determination is a rapid process that occurs within one month. The inflorescence consists of different ultimate floral structural components. Pistillate flowers are borne in floral triads that are flanked by two functional staminate flowers. The staminate flowers are born in floral diads towards the base of the rachilla followed by solitary flowers in the middle to top of the rachilla. Three primary phases were identified in reproductive development, namely, transition of axillary bud into inflorescence bud, formation of floral buds, and sexualisation of individual flower buds. All developmental events with respect to stage or time of occurrence were determined.     

SEX DIFFERENTIAL FLORAL LONGEVITY,NECTAR SECRETION,AND POLLINATOR FORAGING IN A PROTANDROUS SPECIES

Sex differential nectar production, floral longevity and pollinator foraging were examined in Lobelia cardinalis, a self-compatible, protandrous species that is hummingbird pollinated. The staminate phase of the flowers lasts significantly longer and produces significantly more nectar (total sugar) per day than the pistillate phase of the flowers. Additional pollen is presented throughout the staminate phase. Because inflorescences of L. cardinalis mature acropetally, the nectar reward on any given day is greatest at the top of the inflorescence (where staminate phase flowers are located). Hummingbirds appear to be sensitive to this pattern of nectar presentation as they most commonly began foraging in the middle of an inflorescence and proceeded upward. This foraging pattern tends to promote outcrossing and suggests that staminate phase flowers are visited more often than pistillate phase flowers. We conclude that L. cardinalis emphasizes the male function at anthesis. Others have hypothesized that the features of this species are a logical consequence of intrasexual selection, but further research is needed before we place great confidence in a sexual selection interpretation of our data.     

Observations of inflorescence patterns and flower sex in a population of Sagittaria papillosa Buch. (Alismataceae)

Sagittaria papillosa Buch. is monoecious with unisexual flowers, pistillate below, staminate above, typically with an unbranched scape. A large population with unusual numbers of staminate and bisexual flowers on the lowest whorl of the inflorescence and many particles was quantitatively evaluated. First-formed inflorescences had more staminate and bisexual flowers than those produced later. Branched scapes were predominantly found to be the second inflorescence produced by a given plant. Genetic crosses between flowers on recemes and panicles produced no branched inflorescences. When grown under greenhouse conditions all tested plants had racemes with pistillate flowers in the lower whorls and staminate ones above. Data from soil parameters, daylengths and air temperatures are compared to reported information on modification of flower sexuality by these factors.     

Anther structure and pollen development in Melicoccus lepidopetalus (Sapindaceae): An evolutionary approach to dioecy in the family

Anther and pollen development in staminate and pistillate flowers of dioecious Melicoccus lepidopetalus (Sapindaceae) were examined by light and electron microscopy. Young anthers are similar in both types of flowers; they consist of epidermis, endothecium, two to four middle layers and a secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents compressed epidermal cells and endothecium cells with fibrillar thickenings. A single locule is formed in the theca by dissolution of the septum and pollen grains are shed at two-celled stage. The mature anthers of pistillate flowers differ anatomically from those of staminate flowers. The epidermis is not compressed, the endothecium does not develop fibrillar thickenings, middle layers and tapetum are generally persisting, and the stomium is nonfunctional. Microspore degeneration begins after meiosis of microspore mother cells. At anthesis, uninucleate microspores and pollen grains with vegetative and generative nuclei with no cytokinesis are observed. Some pollen walls display an abnormal exine deposition, whereas others show a well formed exine, although both are devoid of intine. These results suggest that in the evolution towards unisexuality, the developmental differences of anther wall tissues and pollen grains between pistillate and staminate flowers might become more pronounced in a derived condition, such as dioecy.     

GA application induces alteration in sex ratio and cell death in <Emphasis Type="Italic">Jatropha curcas</Emphasis>

Jatropha curcas L. is a commercially important plant with biodiesel and medicinal potential. It is a monoecious plant with staminate and pistillate flowers in same inflorescence with number of staminate flowers being higher than pistillate ones resulting in very low fruit yield. Altering sex ratio to increase the number of female flowers would lead to better yield. Phytohormones are most important factors known to alter sex ratio in plants. The mechanism by which phytohormones alter sex ratio differs in different plant species. Among phytohormones, GA plays an important role in sex alteration. In this study, we report the effect of exogenous application of GA on sex modification in J. curcas. There was considerable increase in number of female flowers by application of GA. At lower concentrations (10 and 100 ppm), increase in number of female flowers and fruit yield was proportionate to the concentration of hormone used but at higher concentration (1,000 ppm) though there was an increase in number of female flowers, fruit yield decreased. This was due to an increased peduncle length and enhanced cell death as a consequence of endogenous release of hydrogen peroxide in response to increased GA, resulting in withering of fruits.