A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

The pollination ecology of Pedicularis rex subsp. lipkyana and P. rex subsp. rex (Orobanchaceae) from Sichuan, southwestern China

Pedicularis is one of few genera for which pollination ecology has been studied extensively. Although over half of the species of Pedicularis are found in the mountains of southwestern China, pollination ecology has been studied there on a few species only. The present paper reports pollination ecology of Pedicularis rex subsp. lipskyana and P. rex subsp. rex from Sichuan, southwestern China. The two subspecies are nectariferous, with sugar content 28% in P. rex lipskyana and 22% in P. rex, respectively. The flowers of the two subspecies are adapted to pollination by bumblebee workers. Bumblebees are the primary and effective pollinators although honeybees were also observed pollinating P. rex subsp. lipskyana at one studied population. Usually bumblebees entered the corolla tube from the right side in an upright or a nearly half-inverted position to imbibe nectar located at the base of the corolla tube. The stigma usually contacts the side region of the thorax and abdomen or occasionally directly contacted pollen loads, leading to pollination of flowers. Much less commonly, bumblebees foraged on flowers of P. rex subsp. rex in an inverted position for pollen, which pollinated flowers sternotribically. We suggest that pollination mechanism is closely associated with floral morphology. Some important differences were found from a previous study on P. rex in floral morphology and the primary pollination mechanism.     

Temporal variations in the linkages between plants and flower visitors and the pollination success of Primula modesta along the snowmelt gradient

Although pollination networks between plants and flower visitors are diverse and flexible, seed production of many plant species is restricted by pollen limitation. Obligate outcrossers often suffer from low pollinator activity or severe interspecific competition for pollinator acquisition among co-flowering species. This study focused on seasonal changes in plant–flower visitor linkages in an alpine ecosystem and examined whether and how this seasonality affected the seed-set of Primula modesta, a self-incompatible distylous herb having long-tubed flowers. First, we recorded the linkages between plants and flower visitors along the snowmelt gradient. Then, pollination experiment was conducted to estimate the degree of pollen limitation over the course of flowering season of P. modesta. Flower visitors were classified by their tongue length based on the morphological matching with P. modesta flowers. As the season progressed, plant–visitor linkages became more diverse and generalized, and the visitation frequency to P. modesta flowers increased. In the later part of the season, however, the seed set of P. modesta was significantly reduced due to severe pollen limitation, presumably because of increased competition for long-tongued pollinators among co-flowering species. The present study revealed that pollinator availability for specialist species may be restricted even when plant–visitor linkages are diverse and generalized as a whole. In the case of P. modesta, morphological matching and competition for pollinators might be the main factors explaining this discrepancy.     

A new technique for monitoring pollen flow in orchids

Summary The orchid Prasophyllum fimbria is pollinated by nectar-feeding native bees and wasps. The pollinia are patially separated from the viscidium by a stipe so that pollinia can be labelled with coloured histochemical stains without interfering with pollinarium removal. Pollen flow was monitored by following the movement of the coloured pollen in several populations of P. fimbria in Western Australia. Statistical analysis confirmed that pollen labelling did not interfere with pollinarium removal or subsequent pollination of the labelled flower. Fifty eight labelled pollinaria were removed by vectors from 16 test spikes, with a total of 125 flowers on 47 spikes receiving labelled pollen. An average of 2 flowers received pollen for every pollinium removed but up to 6 flowers received pollen from a single collinium. No significant differences between mean vector flights and pollen flow distances were detected. On average, geitonogamous transfers only accounted for 22% of all pollinations. This is a simple and inexpensive technique for the direct labelling of pollen with minimal disruption to the pollination system and may have applications in other plant families.     

橙花瑞香的繁殖特性研究

瑞香属植物具有重要的药用和观赏价值,在中国资源丰富,但自然条件下低坐果率限制了该属植物的进一步开发和利用。该研究以橙花瑞香为对象,通过对其有性繁殖及传粉特性的研究,探索其自然坐果率低的原因,内容包括花部特征的测量分析,MTT染色法测定花粉活性,联苯胺-过氧化氢法测定柱头可授性,扫描电镜观察柱头、花粉的形态,传粉者观察,通过花粉胚珠比(P/O)和人工授粉实验推测橙花瑞香的繁育系统类型。结果表明:橙花瑞香的花部结构特殊,管状小花,花药两轮,雌雄蕊分离。花开后的花粉具有活性,柱头具有可授性,扫描电镜下,柱头和花粉的结构没有发育异常,且柱头上有花粉落置。橙花瑞香的传粉者主要是夜间访花的蛾类,访花频率低。P/O及人工授粉实验表明橙花瑞香的繁育系统为专性异交。橙花瑞香的坐果率非常低,自然坐果率为1.4%,人工异花授粉为23.3%,低坐果率可能是受其开花量大、异花花粉限制、资源限制以及花部结构等因素的影响。     

Effectiveness of short‐tongued bees as pollinators of apparently ornithophilous New Zealand mistletoes

Abstract The flowers of two species of threatened New Zealand mistletoes (Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae) have explosive buds that do not open unless force is applied by birds or two species of native short‐tongued bees. Opened flowers are visited by a variety of birds and insects. Although both species of Peraxilla conform to a pollination syndrome of ornithophily, bees may be effective alternative pollinators. We investigated the effectiveness of bees and birds as pollinators of P. colensoi at one site and P. tetrapetala at two sites in the South Island. Bees and other insects outnumbered birds as flower visitors at all three sites. By excluding birds with wire cages, we showed that two bee species regularly open flowers of P. tetrapetala, but only rarely open flowers of P. colensoi. Few pollen grains were deposited when either birds or bees opened buds, so opening buds was not by itself sufficient for adequate pollination. Instead, pollen continued to accumulate over the next 6 or 7 days, even inside cages that excluded birds. Both populations of P. tetrapetala were regularly pollen‐limited, but in different ways. At Ohau, opened flowers gained enough pollen to produce seeds, but many buds were not opened and hence failed to set seed. In contrast, at Craigieburn, nearly all buds were opened, but many of these did not receive enough pollen. These results demonstrate that native bees can partially replace birds as pollinators of mistletoes, despite their apparent ornithophilous syndrome. Ongoing reductions in New Zealand forest bird numbers means that the service bees provide may be important for the long‐term future of these plants.     

ON THE DARWINIAN HYPOTHESIS OF THE ADAPTIVE SIGNIFICANCE OF TRISTYLY

Darwin proposed that the function of the stamen-style polymorphism in heterostylous plants is to increase the probability of legitimate (compatible) pollinations among the floral morphs. Conspicuous pollen trimorphism in tristylous Pontederia cordata enables a test of the hypothesis. Comparison of the composition of pollen loads in naturally pollinated stigmas of intact and emasculated flowers were made at a population in Paugh Lake, Ontario, which was visited primarily by bumblebees. The magnitude of legitimate pollination was analyzed by ANOVA. In intact flowers, significant legitimate pollination was detected in the long-styled morph only. Following emasculation legitimate pollination was evident in the long- and short-styled morphs, with the mid-styled morph just short of displaying significant legitimate pollination. Similar results were obtained by chi-square analysis. It has been suggested that heterostyly may reduce mutual interference between maternal and paternal reproductive function. Two aspects of pollen-stigma interference were investigated in P. cordata. The potential importance of stigmatic or stylar clogging by incompatible pollen was examined by controlled field pollinations and measurements of seed set. The results indicate that prior application of large amounts of incompatible pollen has no significant effect on the seed set of open-pollinated inflorescences. Comparison of legitimate pollen capture in intact and emasculated flowers provided no evidence that the presence of stamens within flowers of the floral morphs interferes with the receipt of legitimate pollen. Pollen-stigma interference remains to be demonstrated in heterostylous plants.     

Effectiveness of buzz pollination in Pedicularis chamissonis: significance of multiple visits by bumblebees

Pollination success of plants is highly susceptible to the frequency of visits and foraging behavior of pollinators. Pollination of the nectarless flowers of Pedicularis species depends on bumblebee workers collecting pollen by vibrating the anthers (buzz pollination). However, little is known about the efficiency of the pollination system. Foraging behavior, pollen removal from anthers and pollen deposition on stigmas of P. chamissonis were studied to assess the effectiveness of buzz pollination in an alpine snowbed population of northern Japan. Although bumblebees tended to visit most of the flowers open at a given time within inflorescences during a single visit, pollen removal rate at the first visit was about 20%, and buzzing period decreased with increasing number of previous visits, resulting in a decreasing proportion of pollen removed per visit as the number of visits increased. These trends enable plants to provide pollen for more pollinators. The number of pollen grains deposited on stigmas was not saturated during the first visit and increased with additional visits. Irrespective of weak self-compatibility, evidence of interference between self and outcross pollen was lacking for seed production. Therefore, buzz pollination in P. chamissonis acts as a mechanism that improves the chance of cross-pollination upon multiple visits if pollinator visitation is frequent.     

Bumble bee behavior and selection on flower size in the sky pilot,Polemonium viscosum

Summary In alpine Polemonium viscosum, plants having sweet-scented flowers are primarily pollinated by queens of the bumble bee species, Bombus kirbyellus. In this paper we ask whether two aspects of the pollination effectiveness of bumble bees, visitation rate and pollination efficiency, vary significantly with flower size in sweet-flowered P. viscosum.(i) Bumble bees visited plants with large flowers on 80–90% of encounters, but visited those with smaller flowers on only 49% of encounters. (ii) However, the gain in pollination that large-flowered plants obtained via increased visitation was countered in part because bumble bees deposited fewer outcross pollen grains per visit on stigmas of large flowers than on those of small ones. When both visitation rate and pollination efficiency are taken into account, the predicted value of a single bumble bee encounter declines from 1.06 seeds for flowers larger than 18 mm in diameter to 0.55 seeds for flowers smaller than 12 mm in diameter. Our results suggest that bumble bee pollinators of P. viscosum prefer flower morphologies that are poorly suited for precise pollination. Such behavioral complexities are likely to place constraints on the evolution of optimal floral design.     

Effects of pollination and pollen source on the seed set ofPedicularis palustris

Habitat alteration can deteriorate plant-pollinator interactions and thereby increase the risk of population extinction. As part of a larger study on the effects of changes in land use on fen grassland vegetation, factors influencing the seed set of a short-lived, endangered wetland plant,Pedicularis palustris, were studied. We conducted field pollination experiments in one large and one small population. To investigate the effect of pollen source on seed set, individual flowers of caged plants were left unpollinated or were pollinated with pollen from the same flower, the same population or another population. To study pollen limitation and flower display, whole plants were subjected to pollinator exclosure, hand pollination or natural pollination. Self-compatibility was high, but differed between populations (61% and 97% of seed set after cross-pollination within populations). Cross-pollination between populations did not significantly alter seed number per capsule. Pollinator exclosure resulted in a very low seed set (<15% of natural seed set), despite high self-compatibility. The most likely explanations for high self-compatibility in combination with low autofertility are geitonogamy as reproductive assurance, selective neutrality of self-compatibility and phylogenetic constraints. Because of low autofertility, the seed set inP. palustris depends on pollinators. In the study populations, natural pollination was clearly sufficient for maximum seed production per plant, but seed set per capsule was significantly pollen-limited in the smaller population. Plants in this population also had a higher maximum percentage of simultaneously open flowers than those of the large population (31% vs. 13%), while flower longevity was generally extended without pollination. It is concluded thatP. palustris may influence pollinator behaviour and therefore the risk of pollen limitation by flower display.P. palustris showed a flexible reaction to differing pollination regimes without losses in overall seed set in the study populations.     

Reproductive biology of Pachira aquatica Aubl. (Malvaceae: Bombacoideae): a tropical tree pollinated by bats,sphingid moths and honey bees

We investigated the reproductive biology, including the floral biology, pollination biology, breeding system and reproductive success, of Pachira aquatica, a native and dominant tropical tree of fresh water wetlands, throughout the coastal plain of the Gulf of Mexico. The flowers present nocturnal anthesis, copious nectar production and sugar concentration (range 18–23%) suitable for nocturnal visitors such as bats and sphingid moths. The main nocturnal visitors were bats and sphingid moths while bees were the main diurnal visitors. There were no differences in legitimate visitation rates among bats, moths and honey bees. Bats and honey bees fed mainly on pollen while moths fed on nectar, suggesting resource partitioning. Eight species of bats carried pollen but Leptonycteris yerbabuenae is probably the most effective pollinator due to its higher pollen loads. The sphingid moths Manduca rustica, Cocytius duponchel and Eumorpha satellitia were recorded visiting flowers. Hand pollination experiments indicated a predominant outcrossing breeding system. Open pollination experiments resulted in a null fruit set, indicating pollen limitation; however, mean reproductive success, according to a seasonal census, was 17 ± 3%; these contrasting results could be explained by the seasonal availability of pollinators. We conclude that P. aquatica is an outcrossing species with a pollination system originally specialized for bats and sphingid moths, which could be driven to a multimodal pollination system due to the introduction of honey bees to tropical America.     

Notes on the floral morphology in Vivianiaceae (Geraniales)

The functional floral morphology of the three genera of Vivianiaceae (= Ledocarpaceae, Geraniales), Rhynchotheca, Viviania and Balbisia, is compared. Likely pollination mechanisms are inferred from morphology and field observations. The flowers of Viviania are nectariferous and apparently zoophilous with nectar as the (primary) pollinator reward. Balbisia has pollen flowers without nectaries, its showy corolla indicates that it is also zoophilous with pollen as sole pollinator reward; bees were observed as flower visitors. One taxon (B. gracilis) may be anemophilous. Rhynchotheca has flowers without petals, with large, pendulous anthers and lacks nectaries. It shows synchronous mass flowering in its natural populations and is evidently anemophilous. A comparison with other Geraniales shows that nectar flowers with small anthers are likely the ancestral condition in Vivianiaceae. This suggests that the pollen flowers with larger anthers of Balbisia and Rhynchotheca may represent an apomorphic condition. The documentation of pollen flowers and anemophily in Vivianiaceae expands the range of known floral and pollination syndromes in Geraniales.     

Neither insects nor wind: ambophily in dioecious Chamaedorea palms (Arecaceae)

Pollination of Neotropical dioecious trees is commonly related to generalist insects. Similar data for non‐tree species with separated genders are inconclusive. Recent studies on pollination of dioecious Chamaedorea palms (Arecaceae) suggest that species are either insect‐ or wind‐pollinated. However, the wide variety of inflorescence and floral attributes within the genus suggests mixed pollination mode involving entomophily and anemophily. To evaluate this hypothesis, we studied the pollination of Chamaedorea costaricana, C. macrospadix, C. pinnatifrons and C. tepejilote in two montane forests in Costa Rica. A complementary morphological analysis of floral traits was carried out to distinguish species groups within the genus according to their most probable pollination mechanism. We conducted pollinator exclusion experiments, field observations on visitors to pistillate and staminate inflorescences, and trapped airborne pollen. A cluster analysis using 18 floral traits selected for their association with wind and insect pollination syndromes was carried out using 52 Chamaedorea species. Exclusion experiments showed that both wind and insects, mostly thrips (Thysanoptera), pollinated the studied species. Thrips used staminate inflorescences as brood sites and pollinated pistillate flowers by deception. Insects caught on pistillate inflorescences transported pollen, while traps proved that pollen is wind‐borne. Our empirical findings clearly suggest that pollination of dioecious Chamaedorea palms is likely to involve both insects and wind. A cluster analysis showed that the majority of studied species have a combination of floral traits that allow for both pollination modes. Our pollination experiments and morphological analysis both suggest that while some species may be completely entomophilous or anemophilous, ambophily might be a common condition within Chamaedorea. Our results propose a higher diversity of pollination mechanisms of Neotropical dioecious species than previously suggested.     

Mating strategies and pollen limitation in a globally threatened perennial Polemonium vanbruntiae

Knowledge of the factors that limit reproduction is critical to an understanding of plant ecology, and is particularly important for predicting population viability for threatened species. Here, we investigated the pollination biology of a globally threatened plant, Polemonium vanbruntiae, using hand-pollination experiments in four natural populations to determine the degree of pollen limitation. In addition, we investigated the mating system and extent to which plants can self-fertilize by comparing geitonogamously and autonomously self-fertilized plants with purely outcrossed and open-pollinated plants. In contrast to several of the more common species of Polemonium, we found no pollen limitation in any of the four populations of P. vanbruntiae over two years. The lack of pollen limitation was best explained by the capacity for P. vanbruntiae to both geitonogamously and autonomously self-fertilize, unlike some of its more common congeners. Geitonogamously selfed flowers set equivalent numbers of seeds when compared to purely outcrossed and open-pollinated flowers. However, autonomously selfed flowers produced significantly fewer seeds, demonstrating that pollinators play an important role as inter- and intra-plant pollen vectors in this system. Our results support the reproductive assurance hypothesis, whereby the ability to self assures fertilization for plants in small populations. Self-compatibility in Polemonium vanbruntiae may decrease extinction risk of isolated populations experiencing a stochastic pollinator pool within a restricted geographic range. In addition, a mixed-mating strategy, including the ability for clonal reproduction, may explain the ability for this rare species to persist in small, fragmented populations.     

Effects of indiscriminate foraging by tropical hummingbirds on pollination and plant reproductive success: experiments with two tropical treelets (Rubiaceae)

Summary In cloud forest at Monteverde, Costa Rica, two common treelets (Palicourea lasiorrachis and Cephaelis elata, both Rubiaceae) depend simultaneously on one hummingbird population (Lampornis calolaema) for pollination. Both species are distylous and self-incompatible. In laboratory experiments, we examined possible effects of indiscriminate foraging by hummingbirds among flowers of both species, as observed in the field, on pollination of Palicourea. In each of 35 trials, captive L. calolaema probed 2 flowers from pin plants of Palicourea followed by 20 thrum flowers of the same species, with either 0, 2, or 10 Cephaelis flowers intervening. We assessed pollen transfer by staining and counting pin pollen tubes growing in thrum styles; counts of 0, 1, or 2 pollen tubes relate directly to seed output (0, 1, or 2 seeds per fruit, respectively). Intervening Cephaelis flowers sharply reduced pollen receipt by thrum flowers of Palicourea and reduced some aspects of pollen dispersal from pins as well, thereby curtailing maternal and paternal reproductive potential of Palicourea. Such effects of interspecific pollen loss on reproductive output may lead to strong competition among some, though not all, combinations of plant species pollinated by L. calolaema or of other plant combinations that share animal pollinators.     

POLLEN DISPERSAL DYNAMICS IN AN ALPINE WILDFLOWER,POLEMONIUM VISCOSUM

The alpine wildflower, Polemonium viscosum, depends on insect visitors for effective pollination. Here, I examine experimentally the effects of pollinator visitation on pollen removal, pollen dispersal success, paternity, and gene flow. Bumble bee pollinators visited donor individuals homozygous for marker alleles at an isozyme (GOT-2) encoding locus and then were presented with arrays of recipient plants lacking the marker alleles. Four aspects of male fitness were estimated for each donor: the number of pollen grains dispersed to flowers of the first recipient visited, the number of offspring sired on that recipient, the proportion of offspring sired in the full array, and the proportion of mates in the array bearing seeds of the donor. Pollen removal was strongly influenced by the number of bee visits to donor flowers. The amount of pollen removed in turn significantly affected the number of pollen grains reaching flowers of the first recipient. However, because seed production decelerates with stigma pollen load, the relationship between pollen export and paternal success at this proximate scale showed diminishing returns. The probability of reaching mates within the array also increased with pollen export. These findings show that floral characters enhancing pollinator visitation rate in P. viscosum have positive effects on paternity and gene flow.     

The effectiveness of heterostyly in preventing illegitimate pollination in dish-shaped flowers

Heterostyly is thought to have evolved because it confers efficiency of cross-pollination. While it can be an alternative to an incompatibility mechanism in tube-shaped flowers, its effectiveness in dish-shaped flowers, such as those of Fagopyrum esculentum, has not been demonstrated. Stigmatic pollen loads were examined over the daily course of pollination in a planted field of this crop species. Natural pollination by bees resulted in 23% of the pollen on pin flowers and 69% on thrum flowers being legitimate. Both flower morphs therefore received the two pollen types in about the same proportions. Pin pollen constituted 74% of the pollen delivered to stigmata, even though the two morphs are present in equal numbers. Pin flowers collected about 75 pollen, and thrum flowers about 25 pollen by the end of the day of anthesis. The net result was about 15 compatible pollen per flower on both floral morphs. These results indicate that heterostyly is associated with excess pin-pollen delivery rather than excess legitimate-pollen delivery in F. esculentum.     

峨眉拟单性木兰的开花生物学特性与繁育系统

为阐明峨眉拟单性木兰(Parakmeria omeiensis)在自然条件结实率低的原因和确定最佳人工授粉时期,该文通过观察峨眉拟单性木兰的开花动态,采用杂交指数估算、花粉胚珠比、花粉活力及柱头活性检测、人工授粉试验等方法对其繁育系统进行了研究。结果表明:(1)植物园保育的峨眉拟单性木兰花期在4月底到5月中下旬,持续17～23 d,雄株始花期比雌株早3～4 d,但两者花期可遇。(2)两性花经检测雄蕊败育,实为功能上的雌性,部分雄株个体的雄花上残留1～2个心皮,其性别分化是通过雌、雄蕊选择性败育形成的,为隐性雌雄异株(cryptic dioecy)。(3)雄花、两性花开放经历佛焰苞开裂、花被片开裂、展开、闭合、二次开放、凋落6个阶段,历时4 d。(4)雄花初次展开时花粉活力最高,达92.8%,开花2 d后活力显著下降;两性花柱头在花被片展开期可授性最强,盛开后柱头部分可授。(5)杂交指数为5,P/O比为2.14×10~4。(6)套袋试验表明,峨眉拟单性木兰不能进行自花传粉,人工异花授粉的结实率和出种数显著高于自然授粉,且不存在无融合生殖。这说明峨眉拟单性木兰繁育系统为专性异交,传粉过程需要传粉媒介,自然条件下结实率低,主要是受传粉昆虫和柱头可授期短的限制。     

Pollen source and resource limitation to fruit production in the rare species Eremosparton songoricum (Fabaceae)

Eremosparton songoricum (Litv.) Vass. is a rare, central Asian desert species which shows lower fruit set and seed set (<16%) than most hermaphroditic species. We hypothesized that fruit production was limited by pollen and resources. To evaluate potential fruit abortion due to pollen limitation, supplemental hand‐pollination was undertaken, the mating system was investigated and the foraging behavior of pollinators was recorded. To investigate possibile resource limitation, flowers and young pods were artificially removed and fertilization were manipulated. The results showed that under natural pollination, the number of pollen deposited on the stigma greatly exceed the number of ovules per ovary. Mating system experiments showed that the species is self‐compatible, but depended on pollinators to set seeds. Supplemental outcross pollination increased fruit set significantly. The most frequent effective pollinator Megachile terminate Morawitz, was observed pollinating many flowers of the same individual plant (74.5±1.3%). These results suggested that fruit production is affected by insufficient outcross pollen rather than by pollen quantity. Removal of 2/3 of the flowers and young pods led to significantly higher fruit set, as did addition of fertilizers (N–P–K: 0.025–0.05–0.013 g, N–P–K: 0.05–0.1–0.025 g) showing that reducing resource acceptors and increasing inorganic resources both helps to improve fruit set. We therefore conclude that reproductive success of E. songoricum is limited by both outcross pollen and available nutrients.     

蛛网萼开花物候、花部特征及繁育系统研究

为探讨蛛网萼(Platycrater arguta)传粉生物学特性,该研究以江西上饶广丰铜钹山国家级自然保护区、江西阳际峰国家级自然保护区蛛网萼为材料,采用野外观察和人工授粉等方法,对蛛网萼开花物候、花部形态及繁育系统进行了研究。结果表明:(1)蛛网萼为伞形花序,种群花期一般在6月中下旬至8月中旬,单花花期为2~3 d,花序花期持续10 d。两个保护区由于年均温度与光照的不同,花期进程有显著不同。(2)蛛网萼可孕花与不孕花从绿色变为白色时对访花昆虫有吸引作用,不孕花能够增加昆虫的访花频率。(3)蛛网萼花粉胚珠比(P/O)为2 520~3 100,杂交指数即是3或4。(4)繁育体系属于以异交为主,部分自交亲和,需要传粉者;熊蜂(Bombus sp.)、四条蜂(Apis florea)和油茶地蜂(Andrena cammelia)是蛛网萼的有效传粉昆虫。(5)套袋和人工授粉结果显示,蛛网萼为兼性自交和异交授粉,异株异花授粉能显著提高坐果率及结籽率,这主要与生境中有效传粉昆虫种类、数量少,花粉传递效率低,种群间基因流交流降低以及柱头自花及同株异花传粉等有关,从而表明在蛛网萼现有生境中植株的早期生殖成功受到影响。蛛网萼种群分布范围扩张以有性繁殖为主,无性繁殖作为重要补充及繁殖保障。