The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

Nutrient content of Abutilon theophrasti seeds and the competitive ability of the resulting plants

Summary Siblings of Abutilon theophrasti, were grown on a nutrient gradient. The plants grown at higher nutrient levels were larger and produced larger and more seeds than plants grown at lower soil nutrient concentrations. There were no differences in germinability of seeds, but the competitive abilities of resulting plants were markedly different.In two different competition experiments designed to eliminate the effects of genotype, seed size, and germination time, by using synchronously germinated seedlings derived from similar size seed from plants grown at different nutrient levels, we found that plants from seeds produced at higher nutrient levels consistently, outperformed plants from seeds produced at the lower nutrient levels. The dominance of seeds produced at higher nutrient levels may be explained by the fact that they had markedly higher concentrations of nitrogen than did seeds produced at lower soil nutrient levels. The additional advantage of increased seed quality to plants controlling more of the nutrient resource than their neighbors would be expected to accelerate their contributions to the gene pool of the population.     

The role of seed depth,litter, and fire in the seedling establishment of amphicarpic peanutgrass (Amphicarpum purshii)

Summary Amphicarpum purshii is an annual grass which mostly grows in disturbed areas of the New Jersey Pine Barrens, USA. It is amphicarpic, producing spikelets (and seeds) both above and below the soil surface. Previous research has shown that subterranean seed production ensures reproduction in the event of a major disturbance such as fire and results in rapid post-burn colonization of these sandy habitats. The effects of fire, litter, and seed depth were further examined by planting subterranean seeds at four depths in 16 litter-covered flats buried at ground level and comparing plants arising from burned flats with those in undisturbed litter-covered flats. At 0 and 1 cm depth, rates of seedling emergence were lowest in burned flats. Surface-sown seeds produced seedlings more likely to desiccate. Sowing depth had a greater influence on most measured characters than burning treatments. The mean depth of subterranean seed placement by Amphicarpum is 3.5 cm and this coincides with the seed depth from which plants showed the greatest height growth, shoot biomass, and reproductive output. In a second experiment, subterranean seeds on the bare soil surface in clay pots were more likely to lose viability and less likely to germinate than seeds protected by litter or burial in soil. In addition to providing protection from fire, placement of seeds below ground in the sandy habitat of peanutgrass provides conditions more suitable for seed survival and subsequent seedling establishment.     

Seedling disease in an annual legume: consequences for seedling mortality, plant size, and population seed production

The effect of seed and seedling mortality on plant population dynamics depends on the degree to which the growth and reproduction of surviving individuals can compensate for the deaths that occur. To explore this issue, we sowed seeds of the annual Kummerowia stipulacea at three densities in sunken pots in the field, which contained either field soil, microwaved field soil, or microwaved field soil augmented with oospores of three Pythium species. High sowing density reduced seedling establishment and seedling size, but these effects were independent of the soil treatment. In the oospore-augmented soil, seed and seedling survival was low. The surviving plants were initially smaller but, at maturity, average plant size was greatest in the oospore-augmented soil, compared to the other treatments. Total population seed production was unaffected by soil treatment, suggesting that the effect of disease was limited to the seedling stage, with surviving plants released from intraspecific competition. To test the hypothesis that the surviving plants in the oospore-augmented soil were more disease-resistant, seeds from each of the sowing density-soil type treatments were sown in a growth chamber inoculation study. No evidence for selection for resistance was found. A second inoculation experiment revealed that oospore inoculum reduced plant numbers and mass regardless of whether field or microwaved soil was used, suggesting that results from the field experiment were not dependent on the use of microwaved soil. The findings of this study indicate that the ecological effects of disease on individual plants and on plant populations are not necessarily equivalent. Received: 13 January 1999 / Accepted: 21 September 1999     

Effects of adding plant nutrients to the gel carrier used for fluid drilling germinating lettuce and onion seeds

Fluid drilled germinating lettuce seeds gave earlier production of larger heads than dry sown natural seeds. The addition of sodium phosphate to the gel with germinating seeds increased seedling growth rate which further advanced maturity and increased head weight. Sodium, ammonium and potassium phosphate added to the gel increased seedling dry weight of onions compared to the germinating seed control which produced larger seedlings than dry seed. However, these early improvements in onion seedling size diminished with time.     

Seed size as an indicator of seed quality: a case study of Primula veris

Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field. Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.     

The effects of fluid drilling and seed covering medium on early carrot production under polyethylene mulch

Ungerminated seeds, fluid-drilled germinating seeds and fluid-drilled uniformly-germinated seeds were sown in furrows that were either uncovered or covered by soil and left unmulch ed or mulched with polyethylene sheet. The effects of these treatments on the emergence and growth of carrots for early harvest were examined. Leaving seeds uncovered or mulching them with polyethylene advanced seedling emergence and increased the percentage that emerged; leaving seeds uncovered also reduced the spread of emergence times and produced seedlings with larger cotyledons. Uniformly-germinated seeds emerged before germinating seeds and both emerged before ungerminated seeds. The best combination of treatments (i.e. mulched, uncovered uniformly-germinated seeds) reduced the mean number of days for emergence from the 52 required by traditionally sown seeds to 29. There was a more variable effect of seed treatments on the spread of emergence times and the percentage emergence. Earlier emergence generally led to roots reaching a marketable size earlier and more uniform emergence led to less variation in root weights at harvest.     

A comparison of two large-scale seed priming techniques

Leek seed lots of high (91%) and low (82%) viability were primed in aerated polyethylene glycol (PEG) solutions in Bubble-columns and by a non-osmotic priming technique in both 1987 and 1988 and the seeds were then sown in the field. Both methods of priming established a similar seed moisture content during treatment and, in the laboratory, produced seeds with more rapid and uniform germination than untreated seeds, with a greater advantage for Drum compared with Bubble-column priming in PEG. In the field, both priming techniques gave seedling emergence responses similar to those from priming in PEG by the laboratory-scale technique on filter paper. Both large-scale priming methods gave earlier and more uniform emergence than untreated seeds and gave similar or slightly higher levels of seedling emergence, except on one sowing occasion when seeds were stored before sowing followed by sowing into a drying seedbed.     

The combined effects of a newly designed dibber drill, irrigation and seed covering treatments on lettuce and calabrese establishment

A comparison was made between seedling establishment following sowing with the Mk2 dibber drill and a conventional coulter drill at three sowing occasions with both lettuce and calabrese. Different seed covering materials used to cover dibber-drilled seed were also compared. With lettuce, the rate and uniformity of seedling emergence and the numbers of seedlings emerging were greater following sowing with the dibber drill than with the coulter drill. Seedling establishment was further improved with irrigation especially when seeds were sown with a small quantity of the hydrophillic polymer, Alcosorb, which avoided associated problems of increased soil impedance. Alcosorb was a more effective seed cover than a peat and vermiculite mix and better suited for mechanical metering. Results indicate that the dibber drill can be considered as a realistic and cheaper alternative to transplanting for establishing later-season lettuce crops. With calabrese, however, percentage seedling emergence on all dibber-drilled plots was lower than that on plots sown with the coulter drill. This result may have been due to seed-coat damage caused as seeds are plunged into the soil during sowing with the dibber drill.     

Phenotypic plasticity and population differentiation in seeds and seedlings of the grass Anthoxanthum odoratum

Summary Seeds of Anthoxanthum odoratum were transplanted reciprocally between a xeric and a mesic field population that were genetically differentiated in adult traits. In one experiment seeds were reciprocally buried in bags in the soil, in a second experiment seeds were reciprocally sown in small plots. For most traits, site effects were much larger than seed-source effects. Germination, emergence, mortality of buried seed and recruitment were significantly higher at the xeric site than at the mesic site, irrespective of population of origin. Seed dormancy, was significantly higher for seed originating from the mesic than from the xeric population. Seedling recruits originating from the xeric population tended to be larger at both sites. Fecundity of seedling recruits depended on the environment; fecundities of plants growing in the xeric site had more than double the fecundity of plants growing in the mesic site. Phenotypic plasticity rather than population differences determined variation in performance in the seed and seedling stages.     

Seedling tolerance to cotyledon removal varies with seed size: A case of five legume species

It is generally accepted that seedlings from large seeds are more tolerant to defoliation than those from small seeds due to the additional metabolic reserves present in the large seeds. However, information on the effects of amount of seed reserves (cotyledon removal) from seedlings resulting from large vs. small seeds on seedling growth and long‐term survival in the field is limited. Five legume species with different sizes of seeds were sown in the field and none, one, or both cotyledons removed 7 days after seedling emergence. Seedling biomass, relative growth rate (RGR) and survival were determined at different time. Cotyledon removal, species, and their interaction had significant effects on seedling growth and survival. During the period between 33 and 70 days, seedlings from large seeds had a significantly lower RGR than those from small seeds. Biomass, RGR, and survival of seedlings from large seeds were significantly reduced by removal one or both cotyledons, whereas those of seedlings from small seeds were not affected. Seed energy reserves are more important for the early growth of seedlings from large seeds than for those from small seeds. The overall effect of cotyledon removal on growth and survival varies with seed size (i.e., energy reserves) with seedlings from small seeds being less sensitive than those from large seeds under field conditions.     

埋深和播种密度对豚草种子出苗及幼苗生长的影响

豚草是一种全球性的恶性入侵杂草,给我国生物多样性及经济发展造成了巨大威胁。为研究豚草种子出苗和幼苗生长的影响因素,采用盆栽实验分析了种子大小（L、M、S）与埋深（2、4 cm和6 cm）或播种密度（2、4粒/盆和8粒/盆）对豚草（Ambrosia artemisiifolia）种子的出苗和幼苗生长的影响。研究结果表明,埋深对豚草种子出苗的影响高于播种密度及种子大小的影响,较浅的埋深有利于豚草种子出苗;出苗率在不同播种密度下均具有较高水平,达到67.9%-100%,这种高出苗率是豚草在不同生境成功定植的原因之一。豚草的幼苗生长受埋深或播种密度的影响大于种子大小的影响,且小种子更易受埋深或播种密度的影响。种子大小显著影响豚草幼苗的株高和基径（P<0.05）,总体上较大种子的株高和基径高于小种子,此外更小的种子会将生物量更多的分配给根以促进幼苗的生长。幼苗的株高和基径在较浅的埋深下更高,而豚草幼苗的单株生物量、单株地上和地下生物量随埋深的增加而增加。播种密度的增加会加剧豚草幼苗之间对水分、营养、光照等资源的竞争,导致其单株地上、地下及总生物量显著降低（P<0.05）。研究发现豚草在浅埋深、低密度生境中更容易入侵成功,因此可以通过对土壤进行深翻,采取替代控制,种植竞争能力强的本地植物等手段有效管理和防治豚草。     

种子特征和播种深度对辽东栎种子萌发和幼苗生长的影响

该文在玻璃温室内的遮阴环境下,采用盆播方法研究了辽东栎种子特征(大小和种皮)和播种深度(0、3、6、10 cm)对种子萌发和幼苗生长的影响。结果表明:(1)辽东栎大种子萌发率、萌发速率、萌发值和萌发指数在所有播种深度均高于小种子。其中非去皮种子萌发率、萌发速率和萌发指数在0 cm播种深度的不同大小种子间差异显著,去皮种子所有萌发参数在6和10 cm播种深度的不同大小种子间均差异显著;去皮可促进大种子萌发,但抑制小种子萌发;不同大小种子所有萌发参数均在0 cm播种深度最大,在10cm播种深度最小。(2)不论有无种皮,大种子萌发幼苗的叶片数、单株叶面积、总干物质质量和根冠比在所有播种深度均大于小种子萌发幼苗;去皮种子萌发幼苗的株高、基径、叶片数、单株叶面积和总干物质质量在所有播种深度均不同程度地小于非去皮种子萌发幼苗,但前者根冠比在0、3、6 cm播种深度大于后者;随着播种深度增大,幼苗株高、叶片数、单株叶面积、总干物质质量和根冠比等生长参数均呈减小趋势,但基径随播种深度增大而增大。     

Positive and Negative Interactions among Individuals of a Root Hemiparasite

Abstract: I studied the effects of a wide range of densities on establishment, survival, growth and reproduction of the annual root hemiparasite Rhinanthus alectorolophus in a field experiment. Seeds of the parasite were sown with those of a mixture of grassland plants as potential hosts. In most plants, seedling survival is strongly reduced by self-thinning at high densities, but in R. alectorolophus the proportion of seeds producing a young plant increased linearly with sowing density, indicating positive interactions among seedlings. Because survival to maturity was not influenced by density, the number of flowering plants per seed sown also increased with density. In contrast, mean plant size and reproduction were strongly reduced at high densities. It is suggested that resource sharing among parasites connected by haustoria is the most likely mechanism responsible for the reduced mortality of seedlings at high densities. The results indicate that facilitation among cohorts of conspecific root hemiparasites can increase the recruitment of young plants. The number of seeds produced per seed sown (a multiplicative fitness measure) was, however, independent of density in Rhinanthus because the early positive effects of density on recruitment were compensated later by the negative effects of crowding on growth and reproduction. Increased survival of seedlings could, however, indirectly increase fitness because it will increase the genetic diversity of offspring and may thus, for instance, reduce the impact of pathogens.     

Sowing and transplantation of Adonis ramosa (Ranunculaceae) for the establishment of a new population in a seminatural broad-leaved deciduous forest floor

Adonis ramosa (Ranunculaceae) is a plant whose risk of extinction is increasing in Japan. In this study, we show that there is a significant possibility of establishing an A. ramosa population by sowing seeds or transplanting plants in a seminatural broad-leaved deciduous forest floor. Immediately after seed collection in early June, seeds were sown either in pots that were watered periodically or in a deciduous forest floor where the soil surface was prepared. In the following spring, 30–40% of the seeds germinated. Of the one-year-old plants buried at a depth of 2 cm and two-year-old plants buried at a depth of 2 or 8 cm in the fall, 96% sprouted leaves in the following spring. However, 79% of the one-year-old plants buried at a depth of 8 cm sprouted leaves. In spring, the number of leaves, the widths of individual plants, and the heights of the two-year-old plants were greater than those of the one-year-old plants. The dry weights of one- and two-year-old plants in fall after one spring growing season increased by 1.6–2.3 times and by 2.3–5.1 times, respectively, compared to the dry weight at the time of transplanting. Also, the dry weights of the plants transplanted at a depth of 8 cm were higher than those of plants transplanted at a depth of 2 cm for both one- and two-year-old plants. The results suggest that the growth conditions at a depth of 8 cm are more favorable than those at a depth of 2 cm.     

Experimental demography of the rare Gentianella germanica: seed bank formation and microsite effects on seedling establishment

The persistence of populations of short-lived species requires regular reproduction and seedling establishment. A persistent seed bank can buffer populations against extinction in unfavourable years. We experimentally investigated seed fate in Gentianella germanica, an endangered biennial species characteristic for species-rich nutrient-poor calcareous grasslands in central Europe. We studied the effect of experimental gaps on seedling establishment from sown seeds and the fate of seeds buried in bags over two years. In December 1993 experiments were established at seven calcareous grassland sites in the Swiss Jura mountains. In spring 1994 seedlings emerged in all plots where seeds had been sown, including previously unoccupied patches. This suggests that limited dispersal within sites contributes to small population sizes. Significantly more seedlings emerged at sites with current populations of G. germanica than at unoccupied sites (5.95% vs 3.40%). Because this difference was not explained by germinations from the natural seed bank it indicates differences in habitat quality. Clipping of the vegetation and disturbance of the soil reduced vegetation cover in the following spring and enhanced seedling emergence. In undisturbed plots 4.5% of seeds sown produced a seedling in spring 1994, whereas in plots with clipped vegetation 9.9% and in disturbed plots 12.7% produced seedlings (p>0.01). This suggests that management measures which create gaps in the vegetation (e.g. grazing) could positively influence population size and persistence of G. geymanica. On average, we recovered 7.55% viable seeds after one year of burial in bags, and 4.05% after two years, indicating that G. geymanica has a persistent seed bank. The demographic data indicate that the number of viable seeds in the seed bank exceeds the number of established plants in a population at least by a factor of 20. Restoration of extinct populations of the species from the seed bank may thus be possible if appropriate management measures are taken within a few years.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (<Emphasis Type="Italic">Ericameria nauseosa:</Emphasis> Asteraceae)

In heterogenous landscapes, seeds settle in some microsites more readily than others, independently of whether those microsites are suitable for germination and subsequent growth, and survival of seedlings. Wild seeds and seedlings of Ericameria nauseosa var. oreophila in the sand-dune ecosystem near Mono Lake, California show both concordance and conflict in where seeds are retained and where seedlings flourish. Using a field experiment, we followed performance of seeds and seedlings (i.e., the rate of germination and successful emergence, initial seedling size, seedling growth and survival over first growing season), by planting seeds of known sizes in pre-identified microsites (windward and lee aspects of interspaces between shrubs, under shrub canopies, and under snag canopies, respectively). Heavier seeds were more likely to germinate and emerge successfully and resulted in initially larger seedlings than lighter seeds. These initially larger seedlings subsequently remained larger over the growing season and lived longer than initially smaller seedlings. Independent of seed and initial seedling size, seedlings that germinated under the canopy of adult shrubs grew larger and survived longer than seedlings that germinated in interspaces (open space with little or no vegetation) or under snags (dead adult shrubs). Seedlings grown under the canopy of adult shrubs experienced significantly less solar radiation and wind-deposited sand than seedlings grown in interspace or snag microsites. Sand burial more than 1 cm was lethal for seedlings. The two variables of seed size and microsite type had by far greater impact on eventual growth and survival of seedlings than did aspect, and the effects of the former two variables were independent of each other. This study amplifies the body of work on E. nauseosa at this site demonstrating that the earliest events in the life history of this long-lived perennial shrub appear to persist through time despite the harsh and variable environment.     

Effects of germination time on seed morph ratio in a seed-dimorphic species and possible ecological significance

Background and Aims Diaspores of heteromorphic species may germinate at different times due to distinct dormancy-breaking and germination requirements, and this difference can influence life history traits. The primary aim of this study was to determine the effect of germination time of the two seed morphs of Suaeda corniculata subsp. mongolica on life history traits of the offspring.Methods Germinated brown and black seeds were sown on the 20th of each month from April to September in a simulated but near-natural habitat of the species. Phenological and vegetative traits of the maternal plants, and number, size and germination percentage of the offspring were determined.Key Results Germinated seeds sown late in the year produced smaller plants that had a higher proportion of non-dormant brown than dormant black seeds, and these brown seeds were larger than those produced by germinated seeds sown early in the year. The length of the seedling stage for brown seeds was shorter than that for black seeds, and the root/shoot ratio and reproductive allocation of plants from brown seeds were more variable than they were for plants from black seeds. Late-germinating brown seeds produced larger plants than late-germinating black seeds.Conclusions Altering the proportion of the two seed types in response to germination timing can help alleviate the adverse effects of delayed germination. The flexible strategy of a species, such as S. corniculata, that produces different proportions of dimorphic seeds in response to variation in germination timing may favour the maintenance and regeneration of the population in its unpredictable environment.     

盐磷胁迫对木麻黄和台湾相思种子萌发及幼苗生长的影响

恶劣环境下,人工海防林因面临养分胁迫而经营困难。为探讨盐、磷胁迫对主要海防林树种木麻黄和台湾相思种子萌发及生长的影响,该研究分别用不同浓度的NaCl(盐)和KH₂PO₄(磷)溶液处理种子和浇灌幼苗,测定种子萌发和幼苗生长指标。结果表明：(1)高盐胁迫显著抑制种子萌发,对幼苗生长有一定影响,但两种植物影响程度不同;台湾相思种子萌发耐盐性高于木麻黄,前者相对盐害率最大值为23.03%,后者为89.15%;随着盐浓度增加,木麻黄和台湾相思种子的发芽率、发芽势、发芽指数和活力指数均降低,对应最大值分别为38.70%、34.67%、18.70、0.055和76.67%、62.22%、48.46、6.11。(2)两种植物的株高和根长随盐浓度增加而降低,木麻黄和台湾相思株高分别为12.29～6.01 mm和48.27～17.33 mm,根长分别为8.57～1.45 mm和33.41～5.88 mm;台湾相思根、茎、叶生物量及根冠比均随盐浓度的增加逐渐减小,木麻黄各处理差异较小。(3)台湾相思的种子和幼苗较木麻黄更耐低磷环境,二者最适磷浓度存在差异;木麻黄种...