Autorotating dispersal units of Getonia floribunda Roxb. (Combretaceae): morphology, aerodynamics and geometrical significance

PDF HTML阅读 XML下载 导出引用 引用提醒 两种集合繁殖体形态及间歇性萌发特性——以蒺藜和欧夏至草为例 DOI: 10.5846/stxb201405090928 作者: 作者单位: 新疆农业大学,新疆农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31360100,40761002) Morphology and intermittent germination characteristics of two types of synaptospermy: a case study of Tribulus terrester and Marrubium vulgare Author: Affiliation: Xinjiang Agricultural University,Xinjiang Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:集合繁殖体(synaptospermy)是荒漠植物为适应恶劣环境条件而演化出的关键性特征,其作为植物生活史特性之一,有助于了解在荒漠环境下集合繁殖体植物的适应策略。蒺藜(Tribulus terrestris)和欧夏至草(Marrubium vulgare)分别为一年生及多年生草本植物,蒺藜扩散单位由一朵花发育而成的集合繁殖体组成,欧夏至草扩散单位由多朵花发育的集合繁殖体和种子组成,以这两种植物为材料,对其集合繁殖体形态、活力、吸水及萌发特性进行初步研究。结果显示:(1)蒺藜集合繁殖体依照发育成熟先后位置在质量、附属物刺的长度、附属物占质量百分比、种子数、活力、吸水量、萌发率及萌发速率均存在显著差异;欧夏至草集合繁殖体质量及吸水量明显大于种子,而活力、萌发率及萌发速率不存在显著差异。(2)萌发位置上,蒺藜集合繁殖体仅在长刺端位置的种子萌发,属非随机萌发,而欧夏至草集合繁殖体萌发不具有规律性,属随机萌发;萌发时间上,蒺藜和欧夏至草集合繁殖体在当季下均只萌发部分种子,具间歇性萌发特性。(3)对不同生活型植物而言,其集合繁殖体附属物对种子的保护、保水、扩散及萌发行为的功能相同,但一年生草本植物的萌发行为侧重于种群繁衍,因此蒺藜集合繁殖体在当季萌发率及萌发速率较高;多年生草本植物的萌发行为侧重于种群扩散,因此欧夏至草扩散单位多样化,且萌发率及萌发速率较低。 Abstract:Female plants protect and adjust their offspring through the morphology of synaptospermy after withering. This adjustment provides elasticity and guarantees heredity and reproduction for a given species. Synaptospermy is a critical characteristic of desert plants that evolved as an adaptation to harsh environmental conditions, and may have important ecological significance for the protection of seed function and cross-pollination between plants. Knowledge about this characteristic of the plant life cycle would increase our understanding about the adaptation strategies of synaptospermic plants in desert environments. Synaptospermy involves the joining of two or more seeds or one-seeded fruit to form a compound dispersal unit. This adaptation is common throughout the plant kingdom, but is largely restricted to arid regions. Out of the many morphological-ecological types that have been distinguished among synaptospermic plants, only a few are mentioned here. Synaptospermy is primarily derived from monospermy. Thus, this adaptation represents an advanced evolutionary stage associated with (1) the degeneration of separation tissues in pods, legumes, loments, and capsules, (2) the formation of abscission tissue in the joints of peduncles and pedicels, and (3) a series of other characteristics. In fact, synaptospermic species are found in genera belonging to phylogenetically advanced groups within their respective families, such as the Brassicinae, Galegeae, Hordeae, and Paronychieae. Fruit that contains synaptospermic seeds are able to establish physiological gradients;thus, spreading germination over time (a major advantage). The dispersal and spreading of germination over time (polyphenic germination) allows a mother plant to reduce competition among its offspring. Polyphenic germination is especially pronounced in synaptospermic seeds. Synaptospermy may be divided into two morphologically different types: (1) diaspores develop from the joined seeds of the carpels of one flower, and (2) diaspores develop from the units of different flowers. None of these dispersal units, which contain up to several seeds in a single diaspore, develops more than two seedlings in one season, indicating that all seeds remain together in the dispersal unit, but are ready to germinate in different years;this phenomenon is called intermittent germination. The annual Tribulus terrestris and the perennial Marrubium vulgare are synaptospermic plants with dispersal units belonging to the two morphologically different diaspore types;M. vulgare also disperses using seeds. Here, we conducted preliminary comparisons and observations on the morphology, vigor, water absorption, and germination characteristics of each dispersal unit. The results showed that mass, length of burs, percentage of appendages accounting for mass, number of seeds, vigor, and water absorption all significantly differed among the synaptospermies of T. terrestris. Conversely, while mass and water absorption significantly differed among M. vulgare dispersal units, no significant differences were observed for vigor, germination, and germination rate. The position of germination in synaptospermy differed between plants. For instance, seeds only germinated on the long thorns of synaptospermids in T. terrestris, indicating nonrandom germination, but no regularity in germination was observed for M. vulgare, indicating random germination. In addition, under the conditions with the highest germination percentage, only part of the seeds germinated in one season for both species, indicating intermittent germination. For different plant life forms, the synaptospermic appendage has the same functions, e.g., protecting seeds, retaining water, dispersing, and germinating. However, the germination behavior of annual plants focuses on population reproduction;therefore, the germination percentage of synaptospermy was high over the season for T. terrestris. Conversely, the germination behavior of perennial plants focuses on population dispersal;therefore, the dispersal units of M. vulgare showed diverse characteristics, with a low germination percentage for the dispersal units over the season. 参考文献 相似文献 引证文献

The distribution of wind-dispersed seeds around a parent tree depends on diaspore and tree traits, as well as wind conditions and surrounding vegetation. This study of a neotropical canopy tree, Platypodium elegans, explored the extent to which parental variation in diaspore and tree traits explained (1) rate of diaspore descent in still air, (2) distributions of diaspores dispersed from a 40-m tower in the forest, and (3) natural diaspore distributions around the parent tree. The geometric mean rate of descent in still air among 20 parents was highly correlated with geometric mean wing loading(1/2) (r=0.84). However, diaspore traits and rate of descent predicted less variation in dispersal distance from the tower, although descent rate(-1) consistently correlated with dispersal distance. Measured seed shadows, particularly their distribution edges, differed significantly among six parents (DBH range 62-181cm) and were best fit by six separate anisotropic dispersal kernels and surveyed fecundities. Measured rate of descent and tree traits, combined in a mechanistic seed dispersal model, did not significantly explain variation among parents in natural seed dispersal distances, perhaps due to the limited power to detect effects with only six trees. Seedling and sapling distributions were at a greater mean distance from the parents than seed distributions; saplings were heavily concentrated at far distances. Variation among parents in the distribution tails so critical for recruitment could not be explained by measured diaspore or tree traits with this sample size, and may be determined more by wind patterns and the timing of abscission in relation to wind conditions. Studies of wind dispersal need to devote greater field efforts at recording the "rare" dispersal events that contribute to far dispersal distances, following their consequences, and in understanding the mechanisms that generate them.

Invasive Asian carps established in the United States spawn in turbulent water of rivers and their eggs and early larvae develop while drifting in the current. The eggs are slightly denser than water and are held in suspension by water turbulence. The eggs are believed to perish if they settle before hatching. It is thus possible to use egg drift modeling to assess the capability of a river to support survival of Asian carp eggs. Data to populate such models include the physical properties of the assessed rivers, and information on egg size, density, and terminal fall velocity (sinking rates). Herein, we present the physical characteristics of the eggs as a function of post fertilization time. We recorded mean egg diameter and terminal fall velocity for eggs from each species during the first five hours of development, and at approximately 12 and 22 hours post fertilization. Eggs of all species reached their maximum size before 4 hours. Water-hardened Silver Carp Hypophathalmicthys molitrix and Grass Carp Ctenopharyngodon idella eggs were similarly sized in our trials, and Bighead Carp Hypophathalmichthys nobilis water-hardened eggs were the largest. After water hardening, Silver Carp eggs sank slowest and Bighead Carp eggs sank fastest. For a given species, smaller diameter eggs generally had faster terminal velocity and had higher specific gravity than larger eggs. These data were used to develop a regression growth model of eggs of three species of Asian carp, which includes time-dependent relations for density and diameter of eggs. Asian carp growth models used in conjunction with egg drifting models provide insights regarding the potential of a river to transport Asian carp eggs in suspension until hatching.

Summary The seed shadow created by wind dispersal around parent trees may be affected by functional traits, as well as wind conditions and surrounding vegetation. This study of one mature tree each of 12 Neotropical species determined the extent to which species variation in diaspore traits vs. tree height and crop size explains (i) rate of diaspore descent in still air, (ii) distributions of diaspores dispersed from a 40‐m tower in the forest, and (iii) natural seed shadows around the parent tree. A model of diaspore wing‐loading to a fitted power explained 66·9% of the variation among species in the geometric mean rate of descent in still air. For a subset of four species, expected dispersal distance was not correlated with actual dispersal distance from the forest tower. For a subset of seven species, variation in wing‐loading0·5 of individual diaspores explained ≤4·3% of the dispersal distance from the parent tree. Measured seed shadows, particularly their distribution edges and area, differed significantly among the 12 species (range in maximum tree height 19–42 m) and were best fit by 12 separate anisotropic dispersal kernels and surveyed fecundities. Measured mean distance was highly correlated with simulated distances from the kernels. The best models, explaining 57·6% of the variation among species in shadow area, and 59·6, 61·6 and 61·7% of variation in mean, median and maximum distances, included maximum tree height, either alone or in combination with crop size, and not diaspore rate of descent. Among 10 species, seed shadow area was not related to rank of seedling shade tolerance. In their highly skewed distributions, most seeds were much closer than the distance of greatest seedling recruitment and in very high density, thus enhancing later density‐ and/or distance‐related seedling mortality. Tree functional traits, rather than the historically emphasized diaspore traits, explain distance distributions of these wind‐dispersed species. Additional exploration of diaspore abscission in relation to wind and the influence of wind patterns after release are needed. A lay summary is available for this article.

Seed dispersal is extremely important for the recovery and restoration of forest communities. Relict tree genus Zelkova possesses a unique dispersal mechanism: mature fruits fall with the entire twig, and the dried leaves that are still attached function as a drag-enhancing appendage, carrying the fruits away from the parent tree. This singular adaptation has never been investigated in Z. abelicea. Drop tests with dispersal units and individual fruits of Z. abelicea were performed in controlled conditions to measure their dispersal velocity and to define their flight mode. Zelkova abelicea uses both slowly falling dispersal units with chaotic motion, as well as fast falling individual fruits using a straight path. The falling velocity of Z. abelicea dispersal units is 1.53 m s-1 , which is virtually identical to that of the East Asiatic Z. serrata (1.51 m s-1 ). In contrast, the falling velocity of individual fruits was m s-1 (Z. serrata: 5.36 m s-1 ). Members of the genus Zelkova, growing today in distant regions, show remarkable evolutionary conservation of the velocity and flight mechanics of their dispersal units. This is surprising because the Mediterranean and East Asiatic Zelkova species have been separated at least 15-20 mya. Zelkova abelicea, although growing in the Mediterranean with completely different forest structure and composition, still uses the same dispersal mechanism. The dispersal capacity of the genus Zelkova is less efficient than that of other wind dispersed trees, and it presumably evolved for short-distance ecological spread and not for long-distance biogeographical dispersal.

Competition can simultaneously favour high dispersal ability (to transport offspring to more favourable habitats) and large seed size (to maximise offspring provisioning). In wind dispersed Asteraceae species, seeds are enclosed within an achene with hair-like projections from the achene form a pappus that acts as a parachute to aid in dispersal. There is potentially an allometric relationship between terminal velocity and pappus to achene volume ratio (dispersal architecture), with changes in dispersal architecture resulting in disproportionately high or low impacts on terminal velocity. We tested the hypothesis that competition induces shifts in dispersal architecture depending on the allometric relationship between terminal velocity and dispersal architecture. We estimated dispersal architecture of diaspores from seven wind dispersed Asteraceae species from environments with low and high neighbour densities. We also estimated diaspore terminal velocity for a subset of these species by recording drop time in a 2 m tube. Diaspores of one species had dispersal architecture promoting higher dispersal under high neighbour density, diaspores of two species had dispersal architecture promoting lower dispersal under high neighbour density, and dispersal architecture was not significantly different between high and low density environments for four of the species. Species showed a common allometric relationship between terminal velocity and dispersal architecture. The allometric relationship predicts dispersal architecture changes across environments differing in neighbour density. Species with dispersal architecture promoting higher dispersal under high neighbour density do so where small increases in dispersal architecture yield large decreases in terminal velocity. Our research suggests that the nature of allometric relationships between traits can help to explain allocation strategies across environments.

Post-dispersal predation on seeds of the semi-desert herbaceous perennial Cryptantha flava A. Nels. (Boraginaceae) was examined as a function of both seed density and microhabitat, under a shrub or in the open. The dispersal unit of this species consists of a deciduous calyx which usually encloses a single persistent nutlet (seed) and three aborted ovules. About 15% of the dispersal units contain two seeds. Density was altered by scattering a constant number of dispersal units over areas of different sizes as they would be following natural dispersal by wind. More seeds were removed from high density than low density plots, but there was no difference between microhabitats and no microhabitat X density interaction. The remains of opened calyces suggested that rodents were primarily responsible for the seed removal. In a separate experiment, predators did not discriminate between oneand two-seeded dispersal units, but they only removed one seed from about 4% of the two-seeded dispersal units that they opened. Thus seed predators may be an important selective force maintaining adaptations for wind dispersal but probably have little effect on the number of seeds that mature per dispersal unit.

Biogeography and diversification dynamics of the megadiverse plant genus Cyperus (Cyperaceae, Poales).

<p class="abstract"><strong>Background:</strong> Acne is one of the most common disease affecting adolescence. Although prior studies have evaluated epidemiologic patterns of acne in different ethnicities and regions, literature is lacking from this part of the country. The objectives of the study were to delineate the clinical and epidemiological profile of acne vulgaris in a population from northern Kerala in South India.</p><p class="abstract"><strong>Methods:</strong> The study was carried out for 6 months and it included 100 patients. Epidemiology including pattern, aggravating factors, seasonal variation, diet, smoking, markers of androgenecity and associations were evaluated in all newly diagnosed cases of acne vulgaris who attended the outpatient department in Kannur Medical College, Kannur, Kerala, India from January 2018 to June 2018.<strong></strong></p><p class="abstract"><strong>Results:</strong> Out of 100 patients females (74%) outnumbered males (26%) and although the majority affected belonged to the age group of 21-25 years (38%), adult acne was observed in 28%. Grade 3 acne was the commonest (44%), followed by grade 2 (30%) and grade 4 (18%). Face was affected in all patients with cheeks (91%), followed by forehead (72%), mandible (36%) and chin (28%) and trunk (23%). Scarring was found in 34% and pigmentation in 40%. Family history of acne was observed in 33%.</p><p class="abstract"><strong>Conclusions:</strong> This study brings out the clinical profile of acne in a tertiary care hospital in South India.</p>

D3: The Dispersal and Diaspore Database – Baseline data and statistics on seed dispersal

Delphinieae (Ranunculaceae) comprise ∼650 species of temperate herbs in Eurasia, North America, and Africa. Their zygomorphic flowers have been the object of numerous studies in morphology, ecology, and developmental genetics, and new phylogenetic insights make it timely to synthesize knowledge about their evolution. Key features of Delphinieae flowers are unusual nectaries consisting of paired organs of the inner perianth whorl that are completely enclosed by a single dorsal organ of the outer whorl. We investigated the floral development of five annual, unicarpellate species of Delphinium, focusing on perianth organization. The results show that the nectar-storing organ in these species results from the postgenital fusion of two primordia of the internal perianth whorl. Eleven floral traits traced on a phylogeny of Delphinieae reveal only two homoplasies in the perianth, namely, the nightcap shape of the dorsal organ of the external perianth whorl and the reduction of the internal perianth whorl to two ...

A 2.5D, time-dependent magnetohydrodynamic model is used to test the proposition that observed type II spicule velocities can be generated by a Lorentz force under chromospheric conditions. It is found that current densities localized on observed space and time scales of type II spicules and that generate maximum magnetic field strengths ?50 G can generate a Lorentz force that accelerates plasma to terminal velocities similar to those of type II spicules. Maximum vertical flow speeds are ~150-460?km?s?1, horizontally localized within ~2.5-10?km from the vertical axis of the spicule, and comparable to slow solar wind speeds, suggesting that significant solar wind acceleration occurs in type II spicules. Horizontal speeds are ~20 times smaller than vertical speeds. Terminal velocity is reached ~100 s after acceleration begins. The increase in the mechanical and thermal energy of the plasma during acceleration is (2-3) ? 1022?ergs. The radial component of the Lorentz force compresses the plasma during the acceleration process by factors as large as ~100. The Joule heating flux generated during this process is essentially due to proton Pedersen current dissipation and can be ~0.1-3.7 times the heating flux of ~106?ergs?cm?2?s?1 associated with middle-upper chromospheric emission. About 84%-94% of the magnetic energy that accelerates and heats the spicules is converted into bulk flow kinetic energy.

Long‐distance dispersal (LDD) of plant seeds by wind is affected by functional traits of the species, specifically seed terminal velocity and height of seed release above the vegetation cover (HAC), as well as by the meteorological parameters wind speed and vertical turbulence. The relative importance of these parameters is still under debate and the importance of their variability in vegetation types, sites and years has only rarely been quantified. To address these topics, we performed simulation studies for different vegetation types, sites, years and plant species with PAPPUS, a process based trajectory model. We found that LDD (measured in terms of migration rates) was higher in forests compared to open landscapes. Forests also showed greater between‐year variability in LDD. Terminal velocity had an effect on LDD in both vegetation types, while the effect of HAC was significant only in the open landscape. We found considerable differences in how vertical turbulence and wind speed affect LDD between species and vegetation types: In the open landscape the strength of the positive relationship between vertical turbulence and LDD generally decreases with terminal velocity, whereas it increases in forests. The strength of the predominantly positive effect of wind speed on LDD increases with terminal velocity in both vegetation types, while in forests we found even negative relationships for species with low terminal velocity. Our results generally suggest that the effects of vertical turbulence and wind speed on LDD by wind diverge for species with different functional traits as well as in different vegetation types.

SUMMARYThe role of the involucral bracts of the Compositae capitulum in fruit dispersal, the behaviour of the pappus of composite fruits to changes in humidity, and the presentation of the achene‐pappus units for wind dispersal, are briefly reviewed. Arguments put forward in the literature for and against the effectiveness of the pappus in facilitating wind dispersal are presented. A method is described for comparing the dispersal efficiency of achene‐pappus units of selected composites. The computed trajectories for fruits of selected species under the independent effects of wind speed and plant height, wind speed and boundary layer, and the combination of these with convection velocity are given.It is shown that the efficiency of dispersal is determined more by the fine details of the pappus geometry, which directly affects its aerodynamic properties, than by the size ratio of pappus to achene. Under steady horizontal winds, increased height of fruit release increases dispersal distance. Reported patterns of wind dispersal are discussed in terms of air movement, flight path interference by neighbouring plants and, for some species, the fruit dissemination mechanism.While increased wind velocities increase the trajectory distance, dispersal of many composites is hampered by the pappus response to humidity. Increased dispersal distances are given by steady convection currents, whereas turbulence may either curtail or prolong transportation.The apparent inefficiency of wind dispersal reported under field conditions is explained by the combined effects of these various environmental factors upon the dispersal units during the period of dissemination.

Southeast Asia is the world’s most polluted area in terms of marine plastics. The Mekong River is one of the largest rivers in the area, and ranked as somewhere between the 8th- and 11th-biggest contributor to plastics in the world’s oceans. Here, we investigate how microplastics drift from the Mekong river to Southeast Asia, and which coastlines are most exposed. We identify potential factors (wind drift, rivers, vertical mixing and sinking rates) that affect plastic drift in the region using the OpenDrift model with realistic wind and ocean currents for simulations between three months (summer and winter) and 15 months. We find that the seasonal drift is influenced by the monsoon systems and that most of the plastics strand in the Philippines and Indonesia. In addition, the role of wind drift is significant in strong winds. Vertical mixing and sinking rates are unknowns that affect the relative importance of wind drift (near the surface) and ocean currents. Simulations with different terminal velocities show that, unsurprisingly, the higher the terminal velocities are, the closer they deposit to the source. In light of the large uncertainties in sinking rates, we find that the plastic distribution has large uncertainties, but is clearly seasonal and influenced by wind, vertical mixing, river discharge and sinking rates. The Philippines and Indonesia are found to have the coastlines that are most exposed to plastic pollution from the Mekong river. This study shows that simulations of marine plastic drift are very variable, depending on many factors and assumptions. However, it provides more detailed information on marine plastic pollution in Southeast Asia, and hopefully helps authorities take more practical actions.