Seed size and shade-tolerance: a comparative analysis of North American temperate trees

Large seed size is a trait associated with plant species of mature, closed habitats, and is thought to supply an ample nutrient reserve necessary for seedling establishment. While this relationship has been shown for annuals and short-lived perennials, it is poorly documented for trees. A comparative method was used to determine whether North American temperate tree species which typically establish in shady conditions have larger seeds than those requiring more open conditions. Both angiosperms (hardwoods) and gymnosperms (conifers) were involved in the study. A significant relationship was found between large seed mass and shade-tolerance for angiosperms, but not for gymnosperms. These contrasting results seem to relate to unique evolutionary opportunities or constraints in different taxa. The absence of a relationship for gymnosperms is discussed in terms of character traits which might prevent seed size selection in response to shade. The finding for angiosperms underlines the importance of the regeneration niche in promoting coexistence among temperate hardwood species through seed size differentiation. Received: 18 March 1997 / Accepted: 26 November 1997     

The fate of sheep-dispersed seeds: Plant species emergence and spatial patterns

Sheep epizoochory has often been proposed as an important vector which can help to overcome the dispersal limitation of plants in fragmented landscapes. In order to evaluate the contribution of herbivores to recruitment especially of target species, the dispersal and post-dispersal fate of such seeds must be known. In a field experiment sheep with seeds of mainly target species (experimentally attached to their coats) were present at three sand plots for 24 h. Natural epizoochorous dispersal was already shown for most of the species in our study area. Seed detachment, trampling intensity and seed shadow were measured; seedling emergence and survival were recorded over an 8-month period. In addition, the effect of sheep trampling on seedling emergence and survival of two threatened species, Jurinea cyanoides and Koeleria glauca, were studied.     

滇重楼种子水浸液对三种植物种子萌发和幼苗生长的影响

利用滇重楼(Paris polyphylla Smith var.yunnanensis(Franch.)Hand.-Mazz.)种子外种皮和胚乳的水浸液对白菜(Brassica pekinensis(Lour.)Rupr.)、绿豆(Vigna radiata(Linn.)Wilczak)、小麦(Triticum aestivum L.)种子进行处理,研究滇重楼种子水浸液对3种植物种子萌发、幼苗生长和保护酶活性的影响,并利用GC-MS方法对滇重楼种子内源抑制物的成分进行分析。结果显示,不同浓度滇重楼外种皮、胚乳水浸液对上述3种受体植物的发芽率、苗高、根长及鲜重均产生影响,其作用强度和水浸液的浓度有关,总体上表现出低促高抑的双重浓度效应。滇重楼种子水浸液对白菜的影响作用最强,对绿豆的影响作用最弱,且胚乳水浸液的影响较外种皮强。不同浓度滇重楼种子外种皮和胚乳水浸液均能影响3种植物幼苗体内保护酶的活性,随着水浸液浓度的升高,叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)活性总体增加,与对照相比差异显著。白菜、小麦过氧化氢酶(CAT)活性减少,与对照相比差异显著;绿豆过氧化氢酶(CAT)活性增加,但与对照相比无显著差异。利用GC-MS方法从胚乳和外种皮水浸液中分别检出8种和2种物质。研究结果表明滇重楼种子中存在内源抑制物质,可能是导致种子休眠的原因;种子水浸液可能通过影响植物幼苗保护酶的活性进而影响其正常生长;有机酸类物质可能是滇重楼种子内源抑制物之一。     

云南热带种子植物区系

云南热带是指云南东南,南极西南的沿边热带地区,其地理范围在现今热带雨林及热带季雨林分布的区域。其种子植物区系有４９１５种,隶属于１４４７属和２４８科,基本上是热带北缘性质但同时明显表现出向亚热带过渡的特点。经分析,云南热带东西两侧的地理联系,替代现象、特有现象和区系起源和演化上有很大差异。其原因可能有不同地史背景。因此,将云南热带东西两侧划分古热带植物区中两个不同的植物区系地区是合理的,但其范围和     

Growth, senescence and water use efficiency of spring oilseed rape (Brassica napus L. cv. Mozart) grown in a factorial combination of nitrogen supply and elevated CO2

Atmospheric CO₂ enrichment is expected to affect the resource use efficiency of C3 plants with respect to water, nutrients and light in an interactive manner. The responses of oilseed rape (OSR) to elevated CO₂ have not much been addressed. Since the crop has low nitrogen use efficiency, the interactive effects of CO₂ enrichment and nitrogen supply deserve particular attention.Spring OSR was grown in climate chambers simulating the seasonal increments of day length and temperature in South-Western Germany. Three levels of N fertilisation representing 75, 150 and 225 kg ha⁻¹ and two CO₂ concentrations (380 and 550 μmol mol⁻¹) were used to investigate changes in source-sink relationships, plant development and senescence, water use efficiency of the dry matter production (WUE_prod.), allocation patterns to different fractions, growth, yield and seed oil contents. Seven harvests were performed between 72 and 142 days after sowing (DAS).Overall, plant performance in the chambers was comparable to the development under field conditions. While CO₂ responses were small in the plants receiving lowest N-levels, several significant N × CO₂ interactions were observed in the other treatments. Increasing the N availability resulted in longer flowering windows, which were furthermore extended at elevated CO₂ concentrations. Nevertheless, significantly less biomass was allocated to reproductive structures under elevated CO₂, while the vegetative C-storing organs continued to grow. At the final harvest shoot mass of the CO₂ exposed plants had increased by 9, 8 and 15% in the low, medium and high N treatments. Root growth was increased even more by 17, 43 and 33%, respectively and WUE_prod. increased by 23, 42 and 35%. At the same time, seed oil contents were significantly reduced by CO₂ enrichment in the treatments with ample N supply.Obviously, under high N-supply, the CO₂ fertilisation induced exaggerated growth of vegetative tissues at the expense of reproductive structures. The interruption of source-sink relationships stimulated the formation of side shoots and flowers (branching out). While direct effects of elevated CO₂ on flowering can be excluded, we assume that the increased growth under high N and CO₂ supply created nutrient imbalances which hence affected flowering and seed set.Nevertheless, the final seed macronutrient concentrations were slightly increased by elevated CO₂, indicating that remobilisation of nutrients from the sources (leaves) to the sinks (seeds) remained effective. These findings were supported by the lower nitrogen concentrations in senescing leaves and probably increased N remobilisation to other plant parts under elevated concentrations of CO₂. All the same, CO₂ enrichment caused a decline in seed oil contents, which may translate into a reduced crop quality.     

The promotive effect of smoke derived from burnt native vegetation on seed germination of Western Australian plants

Exposure of dormant seed to cold smoke derived from burnt native vegetation had a positive influence on germination in one or more seed provenances in 45 out of 94 species of native Western Australian plants that are normally hard to germinate. When tested under controlled conditions some species showed earlier germination in smoke treatments than controls; in others smoke-treated seeds continued to germinate for several weeks after controls had achieved full germination. In the remainder, treated and control seeds germinated to similar time schedules. A group of 23 species which responded positively had previously been recorded as extremely difficult or impossible to germinate using conventional techniques. These included members of the genera Geleznowia (Rutaceae), Hibbertia (Dilleniaceae), Stirlingia (Proteaceae), Verticordia (Myrtaceae), Actinostrobus (Cupressaceae) and Pimelea (Thymelaeaceae). Both large- and small-seeded species were encountered amongst the positively responding taxa, which encompassed representatives of 15 families and 26 genera of dicotyledons, 5 families and 8 genera of monocotyledons and the gymnosperm Actinostrobus acuminatus. Sowing seeds on smoke-fumigated filter papers or watering with aqueous eluates of smoke elicited similar degrees of stimulation of germination, as did exposure to gaseous smoke in a readily germinating species Anigozanthos manglesii (Haemodoraceae) and the normally intractable species Lysinema ciliatum (Epacridaceae). Exposing recently burnt and unburnt natural bushland sites to smoke, smoked water or smoked dry sand elicited a significant germination response in 15 species. Over one third of the species sampled in the burnt site exhibited germination additional to that caused by the fire. Data are discussed in relation to previous germination studies on Australian and other taxa.     

Alternative seed-handling strategies in primates: seed-spitting by long-tailed macaques (Macaca fascicularis)

Summary The seeds in fruits consumed by primates may be chewed and digested, swallowed and defecated intact, or separated from the flesh and spat out. We show by a combination of close field observations and experiments with caged animals, that long-tailed macaques (Macaca fascicularis) have a remarkably low threshold of 3–4 mm for swallowing seeds and also that wild macaques rarely break them. The seeds of 69% of the ripe fruit species eaten are spat out intact or cleaned outside the mouth and dropped. Seed-spitting significantly reduces the swallowed food bulk and may lessen the risk of releasing seed toxins during mastication. However, it requires that even small fruits are processed in the mouth one or a few at a time. We suggest that fruit storage in the cheek pouches of cercopithecine monkeys allows them to spit seeds individually without excessively slowing fruit intake while feeding on patchily distributed fruit. In contrast, Apes and New World monkeys apparently swallow and defecate most ripe seeds in their diet and colobine monkeys break and digest them, detoxifying seed defenses by bacterial fermentation.     

邢台西部山地种子植物区系地理研究

邢台西部山地位于河北太行山脉南段,共有野生种子植物93科、393属、823种。该区系地理成分复杂,具有明显的温带性质,也有一定的热带亲缘,中国特有种丰富。运用相似性系数,对该区与其它8个山地植物区系成分进行了比较分析。结果表明:邢台西部山地植物区系与太岳山和中条山区系相似性较高,与东灵山、小五台山、雾灵山和伏牛山的关系次之,与长白山和神农架的相似性较低。     

Germination traits and seed-bank dynamics of a biennial plant,Oenothera glazioviana Micheli

A study was conducted on the germination traits and seed-bank dynamics ofOenothera glazioviana (=O. erythrosepala), which sets seed in August in sand-dune systems in Japan. More than 90% of freshly matured seeds germinated over a wide range of temperature in light, but less than 10% did so in continuous darkness. Stratification (chilling under moist conditions) was ineffective in diminishing the light-requirement for germination. When fresh seeds were imbibed for 24 h including a 12-h light period, followed by 7-day air-drying, 94% of them became germinable in the dark at 25°C, but remained dormant at less than 15°C. of seeds collected in March from capsules of dead plants, 58% germinated in the dark at 25°C. After four cycles of alternatc 1-day wetting followed by 2-day drying or 1.5-day wetting followed by 1.5-day drying under a 12-h photoperiod, the fraction of viable seeds declined from 76% to 40% and 22%, respectively, due to germination during the wet periods. Seed-bag experiments were conducted in the field, using seeds given and not given a light-stimulus. Forty percent of the light-stimulated seeds germinated in the soil, whereas the seeds without a light-stimulus remained dormant throughout the experiment. When seeds were placed on the soil surface or at a depth of 0.5-1 cm, the proportion of germinable seeds declined during late spring and autumn, but not during winter and early spring. The seed-bank size of a natural population just prior to current seed dispersal was 2–3% of the seed production in the previous year, suggesting a high turnover rate of the seed-bank.     

湖北省荆门荆山余脉种子植物区系研究

对湖北省荆门荆山余脉种子植物区系进行了统计分析。结果表明:(1)物种多样性丰富,共有野生种子植物128科、576属、1226种;(2)优势科、属明显;(3)分布区类型多样,地理成分复杂;(4)温带性质明显,热带成分丰富,与热带植物区系有较高的亲缘关系,并表现出一定的过渡性;(5)区划上属于华东植物地区。