Population ecology of an afro-tropical savanna herb,Lapeirousia rivularis,in Zambia

Detailed demographic studies of herbaceuos plants in afro-tropicalsavannas are extremely rare in published literature. I studied phenology andpopulation dynamics of a perennial herb, Lapeirousiarivularis Wanntorp, at a savanna site in Zambia over a 4-yearperiod, from 1997 to 2001, using enumeration techniques in permanent andtemporary quadrants. The age of the plants was accurately determined frompersistent annual sheaths that accumulate around the corm throughout the lifeofthe plant while the estimated survivorship of the 1998 cohort was developedfroma mathematical model based on the observed mortality of the cohort over a3-yearperiod.L. rivularis completed its annual phenological cycle in asingle rainy season. Plants sprouted from perennating corms in early December,flowered, fruited and dispersed seeds by end of January. Seeds germinatedimmediately after dispersal and seedlings produced small corms before aerialparts died early in the dry season. L. rivularis has twomorphs: a vegetative morph and a reproductive morph; the latter bears severalleaves and flower stalks. In the vegetative morph, the corm is renewed annuallywhile the corms of the reproductive morph did not appear to be renewed. Insteadcorms grew larger and produced lateral daughter corms that became independentramets the following rainy season.Most L. rivularis plants reached reproductive maturitywhen they were 6–10 years old. Reproductive success, seedlingestablishment and recruitment varied from year to year in the grassland plotperhaps because of fluctuations in weather conditions and heavy episodic insectherbivory. The survivorship curve of L. rivularis wascharacteristically concave due to high juvenile mortality (0.2–0.5) andvery low adult mortality (0.03). Although about 3% of the plants live to be upto 30–35 years, the mean age of the population in 2001 was 6.4 yearsbecause of the predominance of juvenile plants. The production of a protectivesheath at the end of the rainy season and the accumulation of old sheathsaroundthe fleshy corm are apparent adaptations against desiccation during the longdryseason drought when the topsoil remains below wilting point. The high juvenilemortality during the dry season is probably caused by inadequate protection bythe few sheaths around the corm against desiccation.Population dynamics in L. rivularis were caused byvariable annual recruitment and high juvenile mortality. Population densitydoubled in 1999 due to good fruiting success in the previous season that wasassociated with good weather conditions and negligible herbivory. Althoughcultivation had a significant negative effect on the population of L.rivularis, it increased consistency in fruiting success andproduction of fruits per plant, presumably because of improvement insoil-moisture status, reduction in plant competition and by providing temporalescape from insect herbivory through delayed flowering. The phenology and lifehistory of L. rivularis exhibit adaptations to a savannaenvironment that is characterized by disturbance and stress caused by seasonaldrought, fire, episodic herbivory and cultivation.     

根茎型植物扁秆荆三棱对光照强度和养分水平的生长响应及资源分配策略

自然界中光照和养分因子常存在时空变化,对植物造成选择压力。克隆植物可通过克隆生长和生物量分配的可塑性来适应环境变化。尽管一些研究关注了克隆植物对光照和养分因子的生长响应,但尚未深入全面了解克隆植物对光照和养分资源投资的分配策略。以根茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)为研究对象,在温室实验中,将其独立分株种植于由2种光照强度(光照和遮阴)和4种养分水平(对照、低养分、中养分和高养分)交叉组成的8种处理组合中,研究了光照和养分对其生长繁殖及资源贮存策略的影响。结果表明,扁秆荆三棱的生长、无性繁殖及资源贮存性状均受到光照强度的显著影响,在遮阴条件下各生长繁殖性状指标被抑制。且构件的数目、长度等特征对养分差异的可塑性响应先于其生物量积累特征。在光照条件下,高养分处理的总生物量、叶片数、总根茎分株数、长根茎分株数、总根茎长、芽长度、芽数量等指标大于其他养分处理,而在遮阴条件下,其在不同养分处理间无显著差异,表明光照条件可影响养分对扁秆荆三棱可塑性的作用,且高营养水平不能补偿由于光照不足而导致的生长能力下降。光照强度显著影响了总根茎、总球茎及大、中、小球茎的生物量分配,遮阴条件下,总生物量减少了对地下部分根茎和球茎的分配,并将有限的生物量优先分配给小球茎。总根茎的生物量分配未对养分发生可塑性反应,而随着养分增加,总球茎分配下降,说明在养分受限的环境中球茎的贮存功能可缓冲资源缺乏对植物生长的影响。在相同条件下,根茎生物量对长根茎的分配显著大于短根茎,以保持较高的繁殖能力;而总球茎对有分株球茎的生物量分配小于无分株球茎,表明扁秆荆三棱总球茎对贮存功能的分配优先于繁殖功能。研究为进一步理解根茎型克隆植物对光强及基质养分环境变化的生态适应提供了依据。     

Embryo origin and development in Crocus sativus L. (Iridaceae)

Abstract

Fruit and seed set were obtained in the triploid Crocus sativus (saffron) either by hand crossing with pollen of the diploid C. cartwrightianus or by free pollination. The morphology of the capsules and seeds was similar in both Crocus species. The embryo is comparatively small, whereas the endosperm is formed of numerous layers of cells with hemicellulose-thickened walls and a cytoplasm containing few lipid and protein reserves. Seed germination gave rise to a white prophyll from which a green leaf emerged. At the base of this leaf, a small corm without tunics developed, which, after leaf desiccation, became dormant. These corms sown separately in pots were again capable of growth and emitted a single long green leaf. Vegetative development of new corms was similar in the diploid and hybrid saffron plants. In sites of past saffron cultivation the beds were found to contain degenerated corms and corms at different development stages. The absence of fruit and seed set in emasculated and self- and out-pollinated plants suggests that saffron does not form apomictic embryos.     

DISTRIBUTION OF CALCIUM OXALATE CRYSTAL IDIOBLASTS IN CORMS OF TARO (COLOCASIA ESCULENTA)

The morphology and distribution of intracellular crystals of calcium oxalate in taro (Colocasia esculenta) was studied by light microscopy. The modified Pizzolato (AgNO₃-H₂O₂) method was used to localize crystals in cleared corm cross sections. Crystals of two forms were found: druses and raphides. The numbers and density of the crystals in corms increase rapidly in early development, then level off, and eventually decrease in older and larger corms. An especially high concentration of druses was observed 2-3 mm from the exterior edge of many corms. This corresponds to a ring of vascular tissue which circumscribes the corm at approximately the same distance from the surface. Observations suggest that the development of these highly specialized cells and the formation of calcium oxalate crystals is a dynamic process.     

Harvesting of Onion Grass,Romulea rosea L. by Sulphur‐crested Cockatoo,Cacatua galerita Latham

The harvesting of Onion Grass (Romulea rosea) corms by flocks of Sulphur‐crested Cockatoo (Cacatua galerita) is well known. Individual birds and large flocks feed on the weed in pastures, grasslands and recreational turf. Flocks of Sulphur‐crested Cockatoo were observed feeding on Onion Grass at seven sites along the Maribyrnong River at Keilor, Victoria. Flock size and feeding habits were noted, as were the depth of corms, the time taken to remove corms from the ground and the number of eaten and lifted but uneaten corms. From the data collected, it was estimated that an individual bird can extract and eat about 200 plants per hour and that even a small flock can consume several thousand plants in a feeding session. Corms were typically within 20 mm of the soil surface and were removed primarily by the cockatoo with its beak, but the left foot was sometimes used to excavate the corm from the soil. Flock feeding sessions lasted from about 0.5 to 2.5 hours, but feeding by individual or pairs of birds was often shorter. Plants that had been removed from the soil appeared to have intact corms, but all that was left were the outer scales. Of the plants removed from the soil, only 6% had intact corms attached. The removal of large numbers of Onion Grass plants could impact on their population numbers over time if there was repeated annual harvesting.     

Studies with Liatris spicata Willd. 1. Effect of Temperature on Sprouting, Flowering and Gibberellin Content

Dormancy was induced during storage of Liatris spicata cormsgrown in Israeli summer conditions, but plants left in soilcontinued vegetative growth. Corms of winter-grown plants sproutedfreely. Treatment with GA₃ restored both sprouting and floweringin summer-grown corms, but in winter corms GA₂ was effectiveonly after corms were stored at low temperature. All the plantsflowered after 4 weeks at 2 °C and GA³ treatment. The content of gibberellins in the main bud of freshly excavatedcorms decreased during the first 18 d of storage but increasedto the initial level after 4 months of cold storage. The numberof flowering stems increased to 2.5 per corm when corms werecold-stored up to 75 d, but decreased with a longer storage. Liatris spicata, dormancy, flowering, gibberellin, sprouting     

Diseases of the gladiolus: II. Experiments on dry rot disease caused by Sclerotinia gladioli Drayt

Inoculation experiments show that (1) young corms are more susceptible than old and become less susceptible as they develop, (2) infection of unwounded corms readily takes place, (3) inoculation of the top of an old corm is more effective than that of the side or base.
The percentage diseased new corms produced from infected parent corms varies from o to 100 according to soil conditions. Disease is favoured by wet soil.
Removal of 'husks' (leaf bases) increases the susceptibility of corms planted in contaminated soil, but the presence of husks is not an effective control. Dehusking did not increase the number of diseased young corms in an infected stock planted in new soil.
No variety was strikingly more resistant than the rest.
Good control was obtained when, corms of a diseased stock were treated with mercuric chloride, mercurous chloride (calomel) or the proprietary mercury fungicide Aretan. Calomel gave the most consistent results. Various other treatments were tested in small-scale trials with some success. Red copper oxide, formalin and the proprietary mercury compound, Ceresan, were harmful.
Sterilization of contaminated soil with formalin, mercuric chloride, Aretan or Uspulun gave good but not complete control. Formalin was the least effective.     

The induction of contractile roots in Gladiolus grandiflorus

The number of contractile roots formed in gladioli was inversely related to the depth of the planted corm. Below a certain depth, no contractile roots were produced. Large corms did not produce contractile roots at any planting depth but produced two or more small corms. Depth perception is a function of two independent mechanisms, namely, temperature fluctuations in the root-initiation zone and the amount of light perceived mainly by the upper sheath leaf, the length of which varies with planting depth. Various growth substances applied to the leaves or corms did not induce contractile roots in dark-grown plants but roots were induced by indole-3-butyric acid in both small and large corms grown at constant temperatures and light. Abscisic acid retarded the formation of contractile roots under inductive conditions.Abbreviations CR contractile root(s) - IBA indole-3-butyric acid     

Induction and characterization of in vitro corms of diploid-taro

When in vitro plantlets were cultured in Murashige and Skoog liquid medium supplemented with 8–10% sucrose and 22–44 μM 6-benzylaminopurine, all of the stem explants formed corms. 170–850 μM paclobutrazol increased corm formation, whereas 1700 μM paclobutrazol inhibited corm development. Inclusion of 66 μM 6-benzylaminopurine in 170 μM paclobutrazol treatment resulted in smaller corms, and bigger corms formed in the combination of 1700 μM paclobutrazol and 66 μM 6-benzylaminopurine. No corms formed in 63–630 μM cycocel treatments. In vitro corm growth was also affected by the culture methods. Deep-layer agitated culture yielded corms of up to 2.03 g, with an average fresh weight of 0.7 g, 40 days after induction. In thin layer cultures, corms were up to 1.87 g, with an average fresh weight of 0.5 g. SDS-PAGE analysis of water-soluble proteins revealed changes of polypeptides with corm growth. Compared to smaller ones, corms over 0.2 g had higher dry matter, carbohydrate and anthocyanin content. These corms had a 99–100% survival rate upon transplanting directly to soil after storage at 4 °C for 10 months. This study indicates that the most economic production method of diploid taro seed corm is by thin-layer liquid culture in Murashige and Skoog medium supplemented with 22–44 μM benzylaminopurine and 8–10% sucrose for 6 weeks. The formed corms can be stored at 4 °C up to 10 months and transplanted directly into soil without acclimatization. This revised version was published online in June 2006 with corrections to the Cover Date.     

THE RELATIONSHIP BETWEEN AGE,SIZE, AND REPRODUCTION IN TRILLIUM GRANDIFLORUM (LILIACEAE)

The relative importance of age and size as predictors of demographic parameters such as survivorship or reproductive status is generally unknown for herbaceous perennials, due primarily to the difficulty in estimating the age of herbaceous plants. We investigated the relationship between age, size, and reproductive status in Trillium grandiflorum, a rhizomatous perennial herb in which age can be estimated. We measured the leaf area and rhizome volume and estimated the age of plants in a study population that included reproductive and nonreproductive individuals. Reproductive plants were significantly older ( = 22.8 years) than nonreproductive plants ( = 13.3 years). Reproductive plants also had significantly larger total leaf areas and rhizome volumes. Total leaf area, rhizome volume, and age were positively correlated in both groups. Reproduction in this population occurred once plants reached a threshold leaf area or rhizome volume. Both measures of plant size, i.e., total leaf area and rhizome volume, were better predictors of plant reproductive status than was plant age.     

Composition of Soluble Nucleotides in Growing Corms of Amorphophallus konjac C. Koch

The nucleotides and the activities of both sucrose synthetase and granular starch synthetase in the konjak corm (Amorphophallus konjac C. Koch) have been investigated as a preliminary experiment on konjak mannan biosynthesis. On chromatographic separation on anion exchange resin and paper of compounds present in the acid ethanol extract from the corms, ascorbic acid, AMP, ADP, ATP, ADP-glucose, UTP, UDP-glucose, GTP, and GDP-mannose were isolated and tentatively identified. An unidentified nucleotide was also isolated.

Of the three nucleotide sugars, UDP-glucose was the most plentiful, while ADP-glucose was the least. The sucrose synthetase in konjak corms was as active as that in other plants. These observations suggest that the mechanism involved in sucrose cleavage in konjak corms is the same as that in other plants, such as sweet potato roots. Starch synthetase bound to starch granules in konjak corms was also found to be active when ADP-glucose was used as glucose donor. But UDP-glucose could not be substituted for ADP-glucose.

Based on these observations the mechanism of konjak mannan biosynthesis is discussed.     

Profile of polyamines during sprouting and growth of saffron (Crocus sativus L.) Corms

The profile of free and conjugated polyamines putrescine, spermidine, and spermine was studied at the onset of sprouting and during various stages of vegetative growth in saffron (Crocus sativus L.) corms. Polyamines were extracted from the shoot meristems and estimated by high performance liquid chromatography. Free putrescine was not detected at the onset of sprouting, whereas free spermidine and spermine levels increased rapidly on sprouting and decreased during further stages of corm development. The levels of conjugated polyamines were several times higher than the free forms indicating their possible role in the developmental processes. A comparison of polyamine levels of vegetative and floral corms showed higher titers of free polyamines in vegetative and conjugated polyamines in floral corms.     

Precocious gladiolus corm formation in liquid shake cultures

Conditions were defined for precocious differentiation and improved growth of corms at the base of gladiolus shoots. Shoots were derived from explants cultured on agar solidified media, and corm regeneration was obtained in subsequent liquid shake cultures. Benzyladenine (BA), at 10^-7 M, was found to have a stimulating effect mainly when provided to the shoots prior to manifestation of corm growth. Paclobutrazol and sucrose promoted corm formation when supplemented to the liquid media. Paclobutrazol, at 10 mg l^-1, shifted assimilate allocation towards the growing corm. A differential promotion of corm development by sucrose was not observed, and the concentration of sucrose at which the sugar demand for maximal shoot and corm growth is satisfied (60 g l^-1) was unaltered by the presence of paclobutrazol. The rate of corm growth on shoots cultured in a liquid medium supplemented with paclobutrazol and a saturating sucrose concentration, was a function of the length of the shoot's leaf blades, and was similar in light and in dark.     

The Edible Plant Dichelostemma capitatum: Its Vegetative Reproduction Response to Different Indigenous Harvesting Regimes in California

To more thoroughly understand the ecological effects of harvesting geophytes for food by American Indians, an investigation of the ethnobotany and population dynamics of Dichelostemma capitatum (blue dicks), an attractive source of nutrition to many California Indian groups was undertaken. Some cultural groups harvest the corms and replant the cormlets, spare plants, and harvest after seeding to ensure replenishment of seed. Some Indian elders equate judicious harvesting with the maintenance and enhancement of field populations of this geophyte. A field experiment was conducted to determine the degree to which differences in intensity and timing of harvest, with and without replanting of cormlets, have any effect on corm and cormlet production. We found that harvesting at 100% intensity, through digging up all plants and corms, and without replanting cormlets at the seed stage, significantly reduces numbers of corms and cormlets compared to the controls (no harvest). However, harvesting at 50% intensity, through digging up half of all plants and corms at the flowering or seed stages, without replanting cormlets, was not significantly different from the controls (no harvest). The results suggest that harvesting blue dicks corms with a digging stick in the latter way could yield a sustainable level of harvest. Indigenous harvesting and management regimes may offer some of the best examples of long-term uses and management of the regional flora without detriment to its biodiversity. Restorationists are urged to study and experimentally mimic indigenous disturbance regimes and their ecological effects known to occur historically in various ecosystems. In some cases, areas will greatly benefit from the reintroduction of management and harvesting regimes that authentically simulate ancient indigenous interactions.     

鼎湖山濒危植物紫背天葵的人工栽培

为研究鼎湖山紫背天葵人工栽培适宜的生长基质和气候条件,以组培球茎为材料,比较了自然气候条件下几种混合基质处理对植株生长情况的影响。结果表明：不同配比混合基质的pH值、有机质和铵态氮含量对球茎萌芽和植株的生长均有显著的影响,适合的pH缓冲范围在3．5～4．5之间,表明紫背天葵为喜酸植物。添加黄泥的基质并不适合紫背天葵的生长;泥炭土＋珍珠岩（3：1）混合基质较适宜于紫背天葵的生长,球茎萌芽率达到88％,植株的须根、球茎、叶和株高等指标表现良好。结合栽培物候期分析,球茎的萌芽期在当年11月～次年1月,生长适温在16～25℃之间,相对湿度为90％～95％。     

Reduced temperature,elevated sucrose,continuous light and gibberellic acid promote corm formation in <Emphasis Type="Italic">Watsonia vanderspuyiae</Emphasis>

Storage organ induction in vitro can limit the loss of plants during acclimatisation, and can substantially reduce the time to flower following acclimatisation. An initial experiment lasting 3 months showed that of the four Watsonia species investigated, only Watsonia vanderspuyiae was capable of consistent corm formation. Consequently, a second study investigating light, temperature (10, 15, 20 and 25°C), carbohydrates (sucrose at 3, 6, 9 or 12%) and plant growth regulators [α-naphthalene acetic acid (NAA), N ⁶-benzylaminopurine (BA), abscisic acid (ABA), gibberellic acid 3 (GA₃), paclobutrazol (PAC) and methyl jasmonate (MeJa)], lasting 6 months, was performed. Abnormal corms were produced by W. lepida in response to ABA, but normal corms formed at lower temperatures (10 and 20°C). In contrast, corms were produced in most treatments of W. vanderspuyiae, with BA, PAC and ABA being the only treatments that inhibited corm induction. By examining the product of the proportion corm induction multiplied by corm mass, four treatments superior to the control (20°C, 1 mg l⁻¹ GA₃, 6% sucrose and continuous light) were selected for a factorial design experiment in W. vanderspuyiae. After 3 months, treatments were ranked according to their product. The best four combinations of these four factors all contained GA₃ and were incubated at 20°C, suggesting synergistic interactions between gibberellins and reduced temperature.     

Flower production in relation to individual plant age and leaf production among different patches of Corydalis intermedia

The life history of an organism can be viewed as the combination of allocations made to maintenance, growth, and reproduction. Allocation to these functions are constrained by trade-offs as increased investment to one function may happen at the expense of another. Moreover, because fecundity and survival probabilities are affected by both the state of an individual and by its surrounding environment, optimal allocation to reproduction and growth may vary with both individual size/age and with the habitat in which it lives. In this study we aim to describe how flower production varies with individual plant age and leaf production among different patches of the perennial herb Corydalis intermedia. We take advantage of the construction of the underground storage organ to estimate the age of individual plants which allows us tacitly to relate flower and leaf production to individual age and successional status of the patch. We sampled all individuals present in nine patches from the same forest and estimated their age, flower production and total leaf area. The age distributions showed that each patch was most often dominated by a few and consecutive age classes. In patches where individuals had the oldest mean age, very few or no juvenile age classes were found suggesting that recruitment had ceased. Based on the age distribution of the patches we propose that the dynamics may best be described as metapopulational with colonization of newly formed open forest gaps and a successionally determined extinction as the patch gradually becomes too shaded for recruitment. Both mean flower production, leaf area and age varied significantly among patches. Flower production increased with both increasing age and leaf area. We found no indication of a trade off between reproduction and vegetative growth since flower production showed a positive relation with leaf production even after removing the effect of age. Number of flowers produced by plants of the same age but growing in different patches did not vary indicating that the difference among patches mainly was due to a difference in age distribution. No individuals produced flowers before they reached an estimated age of three years. Production of flowers followed a power function with increasing age. Our data suggests that C. intermedia plants change their allocation strategy with age investing a relatively large amount of energy in flower production immediately after the immature growth phase when recruitment in their patch may be high. Production of flowers then reaches a plateau around the age of 11 years after which number of flowers produced stays constant. This revised version was published online in June 2006 with corrections to the Cover Date.     

钾对番红花球茎膨大的生理生态效应

名贵中药番红花球茎的大小是决定其入药器官—柱头多少的关键,用4个不同K水平的营养液培养番红花,结果表明,随着施钾水平的提高,叶片中的钾含量、叶绿素含量、ATP相对含量及叶片净光合速率也相应提高,使得叶片作为“代谢源”的能力加强．随着施钾水平提高,新球茎富集钾的能力、可溶性糖含量、Vc含量和蛋白质含量也增加,致使新球茎作为“代谢库”的功能也增强,球茎膨大速率加快,本文对钾元素通过加强“源”和“库”的功能来提高番红花球茎膨大速率的机理进行探讨,为番红花的进一步研究与利用提供了新的依据。