黄土丘陵沟壑区主要物种植冠种子库动态及其生态策略

植冠种子库是植物适应环境并应对外界干扰的种子生态策略之一,研究了黄土丘陵沟壑区12种主要植物植冠种子库动态,结果表明:杠柳不具有植冠种子库,其他11种植物均具有植冠种子库;除了黄刺玫种子在翌年5月达到脱落高峰,其他植物大部分种子在冬季脱落,其中杠柳、达乌里胡枝子、茭蒿、黄柏刺和水栒子的大部分种子脱落集中偏早,铁杆蒿和土庄绣线菊的大部分种子脱落集中偏晚;植冠宿存对大部分植物种子的萌发特性表现为促进作用;但不同植物种子的萌发时滞对植冠宿存响应差异较大;9种植物种子在植冠上宿存至翌年2月底,其种子活力仍能维持达60%以上;该区植物表现出不同的植冠种子库策略,通过不同的方式来减少干扰的威胁,提高成功萌发与更新的几率,它们或具有较大规模的宿存量、或调控种子萌发特性、或提高种子维持活力的百分比。此外,全面了解该区植物形成植冠种子库的机理及对应的生态策略还有待于全面、深入的研究。     

Splash seed dispersal by raindrops

Splash seed dispersal by raindrops was investigated for plants in southern Japan. Nine families, 10 genera and 19 species were confirmed as raindrop-dispersed plants. The 10 genera were Gentiana, Gratiola, Chrysosplenium, Mazus, Mitella, Ophiorrhiza, Sagina, Sedum, Trigonotis and Veronica. The method of splash rain dispersal in these species was clarified. Raindrop-dispersed species were all small herbaceous plants with a vertical pedicel and an apically opening fresh capsule when the seeds mature. Open capsules were cup-shaped or boat-shaped and can accommodate raindrops easily. The raindrops splashed the seeds from the capsule. In general, the seeds weighed very little, but they were heavier than powder or dust seeds dispersed by wind. A strong negative correlation was found between seed weight and the number of seeds per capsule. In the case of Trigonotis brevipes (Maxim.) Maxim., raindrops were received into the cup-shaped calyx-tube and dispersed the fruitlets. Some species, such as Gentiana thunbergii (G. Don) Griseb., Gentiana zollingeri Fawcett and Ophiorrhiza japonica Blume, had hydroscopic movement capsules that opened widely only when wet. Raindrop-dispersed plants were found in various habitats. For example, some plants grew together on rocks along the mountain torrents where splash water could easily be caught. The results of the laboratory and field experiments indicated that the dispersal distance of seeds by raindrops was 1m or less. For small herbaceous plants, splash dispersal by rain might be an effective and advantageous method of seed dispersal because dispersal is not affected by plant height.     

Evolution of seed dispersal in North American <Emphasis Type="Italic">Ephedra</Emphasis>

Related plants often produce seeds that are dispersed in very different ways, raising questions of how and why plants undergo adaptive shifts in key aspects of their reproductive ecology. Here we analyze the evolution of seed dispersal syndromes in an ancient group of plants. Ephedra (Gymnospermae; Gnetales; Ephedraceae) is a genus containing ≈50 species in semiarid ecosystems worldwide and with three distinct types of cones. We collected mature cones and seeds of ten species of Ephedra in southwestern United States and measured nine morphological traits for each species. Principal component analysis and other data characterized three types of Ephedra cones and seeds. Species with dry, winged cone bracts are dispersed by wind (i.e., E. torreyana and E. trifurca), those with succulent, brightly-colored cone bracts are dispersed by frugivorous birds (i.e., E. antisyphilitica), and those with small, dry cone bracts and large seeds are dispersed by seed-caching rodents (e.g., E. viridis and E. californica). Two species (E. funerea and E. nevadensis) have cone and seed morphologies intermediate between two seed dispersal syndromes. Seed and cones traits were mapped onto two recent phylogenies to help reveal the evolutionary history of seed dispersal syndromes. Bird dispersal is thought to be the ancestral form of seed dispersal in ephedras as it is common in the Old World where Ephedra originated, but the three North American species dispersed by birds are not monophyletic. The two wind dispersed species in North America also do not cluster together, suggesting separate origins. Seed dispersal by seed-caching rodents is common in North America and appears to have evolved several times, but this syndrome is absent form other continents. The evolutionary history of Ephedra in North America suggests that the means of seed dispersal has been malleable. Evolutionary shifts were likely linked to changes in ecological conditions.     

Role of trichomes and pericarp in the seed biology of the desert annual Lachnoloma lehmannii (Brassicaceae)

In many angiosperms, the fruit rather than the seed is the dispersal/germination unit, and this is the case with Lachnoloma lehmannii, a desert annual ephemeral in central southwestern Asia with indehiscent nonmucilaginuous silicles covered with trichomes. The primary aim of this study was to assess the role of trichomes and pericarp in dispersal, anchorage of diaspores, and seed germination of this species. Mature silicles are dispersed by wind and gravity, and trichomes not only significantly increased their dispersal distance, adherence to sandy soil particles, mass of water imbibed and moisture content, but also decreased the rate of water loss and moisture content of seeds. A significantly higher percentage of seeds within silicles than of isolated seeds retained viability after exposure to 60 °C for 24 h. Seed dormancy is due to the pericarp and to nondeep physiological dormancy, as shown by the increase in germination percentage of isolated seeds following dry storage and treatment with GA₃. Removal of pericarp increased germination of 6-month-old seeds from 0 to 80–90 %, and leachate from both pericarp and trichomes significantly inhibited germination of isolated seeds. Ninety-five percent of seeds within silicles buried in soil for 2 years were viable, but only 28 % of them germinated in light at 15/2 °C; thus L. lehmannii forms a persistent soil seed bank. The pericarp and its trichomes may maximize plant fitness by determining the settlement location of silicles, thus helping to ensure that seeds germinate during the cool season for seedling survival in the desert environment.     

Seed traits and bird species influence the dispersal parameters of wetland plants

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Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

Role of indehiscent pericarp in formation of soil seed bank in five cold desert Brassicaceae species

The dispersal and germination unit of some Brassicaceae species is the fruit, and we hypothesized that it could affect germination phenology and promote formation of a soil seed bank. We determined the effects of the indehiscent pericarp on germination and longevity of buried seeds of five Brassicaceae species native to cold deserts of central Asia. Germination phenology (seedling emergence) was monitored for intact dispersal units and isolated seeds of Chorispora sibirica, Goldbachia laevigata, Spirorrhynchus sabulosus, Tauscheria lasiocarpa (annuals), and Sterigmostemum fuhaiense (perennial) at natural temperatures in watered and non-watered (natural precipitation) soil. Intact dispersal units and isolated seeds were buried under natural conditions and exhumed at regular intervals for 35 months to monitor germination, viability and moisture content of isolated seeds, seeds in dispersal units, and seeds removed from dispersal units after burial. Isolated seeds of Goldbachia, Spirorrhynchus, and Tauscheria germinated only the first autumn and those of Chorispora and Sterigmostemum the first autumn and first spring, with higher germination percentages in all species in watered than in non-watered soil. A high percentage of seeds in buried dispersal units of Chorispora, Goldbachia, and Sterigmostemum was viable after 35 months, and seeds exhibited a 6-month dormancy cycle, being non-dormant only in autumn and spring. Seeds in buried dispersal units of Spirorrhynchus and Tauscheria germinated when exhumed in the first spring, but all non-germinated seeds were dead after 1 year. Thus, the presence of the pericarp allows Chorispora, Goldbachia, and Sterigmostemum to form a persistent seed bank but not Spirorrhynchus and Tauscheria.     

The role of Rhytidoponera metallica (Hymenoptera,Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

The fire avoidance hypothesis proposes that a benefit of seed dispersal by ants (myrmecochory) is to protect seeds from being killed during fire and to facilitate post‐fire germination of seeds that require heat shock to break their physical dormancy. The aim of this study was to quantify the effect of fire and seed burial by a predominant seed‐dispersing ant, Rhytidoponera metallica (subfamily: Ectatomminae) on germination levels of three ant‐dispersed legume species (Pultenaea daphnoides, Acacia myrtifolia and Acacia pycnantha). Experimental burial of seeds within aluminium cans at a site prior to being burnt and at an adjacent unburnt site showed that fire increased germination levels, particularly for seeds buried at 1‐ and 2‐cm deep and that overall, germination levels differed among the three plant species. To quantify seed burial depths and post‐fire germination levels facilitated by R. metallica ants, seeds were fed to colonies prior to fire at the burnt and unburnt sites. Of the seeds buried within nests that were recovered, between 45% and 75% occurred within the upper 6 cm of the soil profile, although unexpectedly, greater percentages of seeds were recovered from the upper 0–2 cm of nests in the unburnt site compared with nests in the burnt site. Germination levels of buried seeds associated with R. metallica nests ranged from 21.2% to 29.5% in the burnt site compared with 3.1–14.8% in the unburnt site. While increased seed germination levels were associated with R. metallica nests following fire, most seeds were buried at depths below those where optimal temperatures for breaking seed dormancy occurred during the fire. We suggest that R. metallica ants may provide fire avoidance benefits to myrmecochorous seeds by burying them at a range of depths within a potential germination zone defined by intra‐ and inter‐fire variation in levels of soil heating.     

Consequences of the timing of seed release of Erythronium americanum (Liliaceae), a deciduous forest myrmecochore

Myrmecochores are plants with seeds adapted for ant dispersal. This specialized dispersal syndrome may provide Erythronium americanum seeds with protection from predators within the eastern deciduous forests. To determine the adaptive significance of myrmecochory in E. americanum, seed removal rates and seed predation in relation to seed release date and location along the Potomac River in Langley, Virginia, were examined. The number of seeds removed from four exclosure treatments were monitored two times in 1992 and three times in 1993 within floodplain and hilltop populations of E. americanum. Overall, seed removal was greatest from control depots, and E. americanum seeds were removed at nearly the same rate from predator-exclusion depots, indicating that removal from open depots is largely due to ant removal. Ants removed significantly more seeds than predators in the first 48 h of seed exposure and could potentially remove all E. americanum seeds before nightfall. Aphaenogaster rudis was identified as the primary disperser of E. americanum. Seeds placed in depots after the natural seed release period were discovered more quickly and removed by ants at a significantly higher rate than seeds released at the natural date. These results suggest that ant dispersal of E. americanum seeds reduces the likelihood of seed predation.     

Effects of seed traits on the potential for seed dispersal by fish with contrasting modes of feeding

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The relative contributions of seed and pollen dispersal to gene flow and genetic diversity in seedlings of a tropical palm

Seed and pollen dispersal shape patterns of gene flow and genetic diversity in plants. Pollen is generally thought to travel longer distances than seeds, but seeds determine the ultimate location of gametes. Resolving how interactions between these two dispersal processes shape microevolutionary processes is a long‐standing research priority. We unambiguously isolated the separate and combined contributions of these two dispersal processes in seedlings of the animal‐dispersed palm Oenocarpus bataua to address two questions. First, what is the spatial extent of pollen versus seed movement in a system characterized by long‐distance seed dispersal? Second, how does seed dispersal mediate seedling genetic diversity? Despite evidence of frequent long‐distance seed dispersal, we found that pollen moves much further than seeds. Nonetheless, seed dispersal ultimately mediates genetic diversity and fine‐scale spatial genetic structure. Compared to undispersed seedlings, seedlings dispersed by vertebrates were characterized by higher female gametic and diploid seedling diversity and weaker fine‐scale spatial genetic structure for female gametes, male gametes and diploid seedlings. Interestingly, the diversity of maternal seed sources at seed deposition sites (N _em) was associated with higher effective number of pollen sources (N _ep), higher effective number of parents (N _e) and weaker spatial genetic structure, whereas seed dispersal distance had little impact on these or other parameters we measured. These findings highlight the importance maternal seed source diversity (N _em) at frugivore seed deposition sites in driving emergent patterns of fine‐scale genetic diversity and structure.     

Assessing ant seed predation in threatened plants: a case study

Erodium paularense is a threatened plant species that is subject to seed predation by the granivorous ant Messor capitatus. In this paper we assessed the intensity and pattern of ant seed predation and looked for possible adaptive strategies at the seed and plant levels to cope with this predation. Seed predation was estimated in 1997 and 1998 at the population level by comparing total seed production and ant consumption, assessed by counting seed hulls in refuse piles. According to this method, ant seed predation ranged between 18% and 28%. A more detailed and direct assessment conducted in 1997 raised this estimate to 43%. In this assessment spatial and temporal patterns of seed predation by ants were studied by mapping all nest entrances in the studied area and marking the mature fruits of 109 reproductive plants with a specific colour code throughout the seed dispersal period. Intact fruit coats were later recovered from the refuse piles, and their mother plants and time of dispersal were identified. Seeds dispersed at the end of the dispersal period had a greater probability of escaping from ant seed predation. Similarly, in plants with late dispersal a greater percentage of seeds escaped from ant predation. Optimum dispersal time coincided with the maximum activity of granivorous ants because, at this time, ants focused their harvest on other plant species of the community. It was also observed that within-individual seed dispersal asynchrony minimised seed predation. From a conservation perspective, results show that the granivorous ant–plant interaction cannot be assessed in isolation and that the intensity of its effects basically depends on the seed dispersal pattern of the other members of the plant community. Furthermore, this threat must be assessed by considering the overall situation of the target population. Thus, in E. paularense, the strong limitation of safe-sites for seedling establishment reduces the importance of seed predation.     

Effects of Seed Dispersal by Three Ateline Monkey Species on Seed Germination at Tinigua National Park, Colombia

We examined the effect of seed ingestion by three ateline primates: woolly monkeys, Lagothrix lagothricha; spider monkeys, Ateles belzebuth; and, red howler, Alouatta seniculus on germination rates and latency periods of seeds of several plant species in Tinigua National Park, Colombia. We collected dispersed seeds from feces and control seeds from the parental trees and washed them for germination trials. For the majority of plants, dispersed seeds germinated as well or better than control seeds did. Although spider monkeys depend more heavily on fruits than the other monkey species do, they were not more efficient than howlers or woolly monkeys at improving germination rates. A considerable proportion of the seeds dispersed by howlers and woolly monkeys showed reduced latency periods to germination, but spider monkeys showed less effect on reducing germination time. This result may be related to longer gut retention times, but such a trend has not been observed in other primate species. We conclude that, like many other primates, ateline monkeys are effective seed dispersers in terms of their effects on the seeds they swallow because they rarely decrease their germination rates. We discuss problems that make interspecific comparisons difficult, such as inappropriate control seeds and differences associated with germination substrates, and we stress the importance of studying other components of seed dispersal effectiveness.     

Asian Tapirs Are No Elephants When It Comes To Seed Dispersal

The elimination of the largest herbivores (elephants and rhinoceroses) from many forests in tropical East Asia may have severe consequences for plant species that depend on them for seed dispersal. We assessed the capacity of Malayan tapirs Tapirus indicus—the next largest nonruminant herbivore in the region—as a substitute for the lost megafauna in this role by studying their ability to disperse the seeds of nine fleshy‐fruited plants with seeds 5–97 mm in length. We combined information from feeding trials, germination tests, and field telemetry to assess the effect of tapir consumption on seed viability and to estimate how far the seeds would be dispersed. The tapirs (N=8) ingested few seeds. Seed survival through gut passage was moderately high for small‐seeded plants (e.g., 36.9% for Dillenia indica) but very low for medium‐ (e.g., 7.6% for Tamarindus indica) and large‐seeded (e.g., 2.8% for Artocarpus integer) plants. Mean seed gut passage times were long (63–236 h) and only the smallest seeds germinated afterwards. Using movement data from four wild tapirs in Peninsular Malaysia we estimated mean dispersal distances of 917–1287 m (range=22–3289 m) for small‐seeded plants. Malayan tapirs effectively dispersed small‐seeded plants but acted as seed predators for the large‐seeded plants included in our study, suggesting that they cannot replace larger herbivores in seed dispersal. With the absence of elephants and rhinos many megafaunal‐syndrome plants in tropical East Asia are expected to face severe dispersal limitation problems.     

Preferential removal of non-injured seeds by an omnivorous ant,Tetramorium tsushimae Emery,in the seed dispersal of Chamaesyce maculata (L.) small

To elucidate roles of an omnivorous ant, Tetramorium tsushimae Emery, against pre-dispersal seed consumers in the seed dispersal of Chamaesyce maculata (L.) Small, the effects of the seed injury by a stinkbug, Nysius plebeius Distat, on the seed removal by the ant and the germination rate were examined in laboratory experiments. The ants of T. tsushimae removed more frequently non-injured seeds than injured seeds. Therefore, low removal frequency of injured seeds by T. tsushimae ants might facilitate the increase in removal frequency of non-injured seeds, consequently leading to efficient seed dispersal of C. maculata. The germination rate of injured seeds that N. plebeius nymphs sucked was conspicuously lower than the non-injured seeds. The germination rate of seeds that T. tsushimae ants carried out of their nest was similar to that of the non-injured seeds. Thus, seed removal by T. tsushimae ants has hardly effects on the germination of these seeds. Therefore, the preferential removal of non-injured seeds by T. tsushimae ants might contribute to the dispersal success of C. maculata seeds. These results might show a novel interaction between myrmecochorous plants and ants in which the assessment of seed quality by ants contributes to the reproductive success of plants.     

The role of avian ‘seed predators’ as seed dispersers

Seed dispersal is a central process in plant ecology with consequences for species composition and habitat structure. Some bird species are known to disperse the seeds they ingest, whereas others, termed ‘seed predators’, digest them and apparently play no part in dispersal, but it is not clear if these are discrete strategies or simply the ends of a continuum. We assessed dispersal effectiveness by combining analysis of faecal samples and bird density. The droppings of seed dispersers contained more entire seeds than those of typical seed predators, but over a quarter of the droppings of seed predators contained whole seeds. This effect was further magnified when bird density was taken into account, and was driven largely by one frequent interaction: the Chaffinch Fringilla coelebs, a typical seed predator and the most abundant bird species in the area and dispersed seeds of Leycesteria formosa, a non‐native plant with berry‐like fruits. These results suggest the existence of a continuum between seed predators and seed dispersers.     

Temporal dynamics of seed excretion by wild ungulates: implications for plant dispersal

Dispersal is a key process in metapopulation dynamics as it conditions species' spatial responses to gradients of abiotic and biotic conditions and triggers individual and gene flows. In the numerous plants that are dispersed through seed consumption by herbivores (endozoochory), the distance and effectiveness of dispersal is determined by the combined effects of seed retention time in the vector's digestive system, the spatial extent of its movements, and the ability of the seeds to germinate once released. Estimating these three parameters from experimental data is therefore crucial to calibrate mechanistic metacommunity models of plant–herbivore interactions. In this study, we jointly estimated the retention time and germination probability of six herbaceous plants transported by roe deer (Capreolus capreolus), red deer (Cervus elaphus), and wild boar (Sus scrofa) through feeding experiments and a Bayesian dynamic model. Retention time was longer in the nonruminant wild boar (>36 h) than in the two ruminant species (roe deer: 18–36 h, red deer: 3–36 h). In the two ruminants, but not in wild boar, small and round seeds were excreted faster than large ones. Low germination probabilities of the excreted seeds reflected the high cost imposed by endozoochory on plant survival. Trait‐mediated variations in retention time and germination probability among animal and plant species may impact plant dispersal distances and interact with biotic and abiotic conditions at the release site to shape the spatial patterns of dispersed plant species.     

A role for fruit structure in seed survival and germination of Swartzia langsdorffii Raddi beyond dispersal

• Diaspore structure has been hypothesised to play a role in seed viability and/or germination of recalcitrant seeds, especially for Swartzia langsdorffii. Thus, this work aims to (i) investigate the in situ contribution of pericarp and aril on seed viability and germination, and (ii) identify morphoanatomical traits of S. langsdorffii diaspores that allow its desiccation‐sensitive seeds to remain viable.
• The role of the pericarp and aril in seed survival and germination was investigated by placing the whole fruit, whole seeds (arillate seed) and bare seeds (without aril) in soil in the forest understorey, assessing germination, emergence, dead, firm and predated seeds, and water content of pericarps, arils and seeds. Correlation analysis was performed between environmental variables and physiological parameters. Histochemical features of diaspores were also investigated.
• Pericarp water content fell after several months, while the aril maintained its water content. Seeds did not lose water even without the presence of the pericarp and aril. However, presence of the pericarp promoted seed water content, viability and germination long after dispersal. The embryo had a thickened outer periclinal cell wall.
• Pericarp and aril are not essential to prevent water loss in seeds, but do help to retain seed moisture, favouring viability maintenance and promoting germination during the rainy season. Morphoanatomical features of seeds are suggested as main factors that reduce water loss. Survival of these desiccation‐sensitive seeds upon dispersal during the dry season appears to be facilitated by multiple diaspore features that prevent viability loss.

     

Experimental determination of seed emergence and carry‐over in the soil seed bank of the herbaceous perennial,Trachymene incisa (Apiaceae)

Abstract Many populations of herbaceous perennial plants contain seeds stored in a soil seed bank. The contribution of seeds to population persistence is an important parameter in population models but germination rates of known‐age seeds are difficult to obtain because individual seeds cannot easily be followed. Although Trachymene incisa Rudge plants produce copious seeds that are dispersed into the soil, the existence of a seed bank has not been confirmed. To quantify the potential for a seed bank fresh seeds of T. incisa were sown into experimental seed banks in the eucalypt‐dominated Agnes Banks Woodland in western Sydney, NSW. A recent fire provided the opportunity to compare germination in the burnt and unburnt vegetation. Density of seed sowing and time of maturation/dispersal of seeds were manipulated in 75 seed cages. Emergence of seeds after 5 months was significantly higher for the earliest planting date but after 1 year, germination of seeds planted in the later weeks increased, and the final germination for all weeks was 28%. Density of sowing and the recent fire did not affect emergence. A second experiment planted over a broader time span (9 weeks instead of 3 weeks) confirmed the effect of planting date but also found significant spatial variation on a scale of tens of metres. Laboratory germination rates of over 70% confirmed that the seeds were viable and non‐dormant when sown in the field cages. The carry‐over of non‐germinated seed in the soil seed bank is estimated to be about 70% after 2 years, implying that a cohort of seeds would not be depleted through germination alone for up to 40 years. The potential for a long‐lived seed bank in this species is interesting because the plants are also capable of resprouting from their rootstock after fire, giving them characteristics of both resprouters and seeders.