Effects of seed passage through slugs on germination

Seed dispersal by invertebrates is mostly external (e.g. by ants). However, internal dispersal (endozoochory) seems to be uncommon due to size limitations. Slugs are generalist herbivores and increasing evidence suggests that they often disperse seeds. Nevertheless, we know very little on the consequences for plant recruitment. Here, we assess the effect of slug seed passage on germination and early seedling establishment of a set of nine common plant species with limited dispersal capabilities (unassisted or ant dispersed). Germination trials were performed under natural conditions (NW of Spain). Size was a clear limitation for seed ingestion: smaller seeds were eaten more readily, whereas only the largest slugs could swallow the largest seeds. All ingested seeds were voided undamaged. Only not-ingested seeds (the biggest) were damaged, with chewing marks in the surface and 0.8% (N = 250) were broken. In some cases, slugs ate the elaiosomes but discarded the seeds. Slug seed passage had an overall positive effect on total germination and sped it up in two species. Elaiosome removal by slugs had also a positive effect in Ulex europaeus seeds (+160%). However, slugs had no effect on early seedling survival and growth of the study species. Our results show that slugs are effective dispersers in terms of seed treatment in the digestive track. However, according to their reduced movement range (in the range of tens of metres; as shown by other studies), they can only provide rather limited dispersal as compared to vertebrate dispersers. This can be nonetheless significant for species with limited dispersal, e.g. unassisted and ant-dispersed plants, for which they act as non-standard dispersers.     

盐胁迫对二色补血草种子萌发的影响

以二色补血草(Limonium bicolor)种子为试验材料,用不同浓度的NaCl、Na2SO4及二者质量比为1:1的混合盐在其种子萌发过程中进行胁迫,调查盐胁迫对种子萌发的影响,并测定萌发过程中种子蛋白质含量、淀粉酶活力及还原糖和总糖含量的变化.结果表明:盐胁迫使二色补血草种子的发芽势、发芽指数和发芽率明显降低,而且随着盐浓度的增鲻加,抑制作用增强;3种盐对种子萌发的抑制作用强度依次为NaCl>混合盐>Na2SO4;二色补血草种子耐盐适宜范围为Na2SO4 1.2%、混合盐0.8%、NaCl 0.5%,耐盐半致死浓度为Na2SO4 2.1%、混合盐1.4%、NaCl 1.1%,耐盐极限浓度为Na2SO4 3.5%、混合盐2.4%、NaCl 2.0%.盐处理后不萌发的种子转入蒸馏水后重新萌发的试验结果表明,盐分胁迫主要是通过渗透效应,抑制种子中蛋白质和总糖的分解,进而延缓或抑制了种子的萌发.     

混合盐碱胁迫对芹菜种子萌发的影响

NaCl、Na2SO4、NaHCO3和Na2CO3按不同比例混合,模拟盐度和pH变化规律与天然盐碱地相似的15种盐碱条件,探讨混合盐碱胁迫对芹菜(Apium graveolens)种子萌发的影响.结果表明:芹菜种子的发芽率、发芽势、发芽指数和活力指数均随盐浓度的升高,pH的增大呈下降趋势.芹菜种子的萌发主要受盐浓度的影响,不同盐浓度间的影响差异大;当盐浓度为200 mmol/L时,基本不萌发.     

Effects of drought stress on seed germination of ornamental sunflowers

The response to drought stress on germination was investigated on three hybrids of ornamental sunflower, ‘Hadar’, ‘Pazit’, and ‘Zohar’. Different levels of water potential [Ψ: 0.0 (control), ?0.15, ?0.30, ?0.45, ?0.60, ?0.75, and ?0.90 MPa] were adopted using polyethylene glycol-6000 (PEG6000) at four germination temperatures (15, 20, 25, and 30 °C). Final germination percentage, mean germination time, germination index, germination rate index, and germination stress tolerance index were used to evaluate the genotype response to PEG-induced water stress. Shoot and root length and fresh and dry weight were measured on seeds germinated at 20 °C under the different levels of water potentials. During germination, the three ornamental sunflowers showed to be more sensitive to suboptimal temperature than to supraoptimal. Decreasing water potential of imbibition solution progressively inhibited and delayed seed germination. Among cultivars, ‘Hadar’ and ‘Pazit’ performed better at temperature lower than 30 °C. ‘Zohar’ showed a lower sensitivity to PEG-induced water stress at all temperature conditions. Water stress during seed germination depressed the following seedling growth under favourable conditions. As a result, shoot and root length and fresh and dry weight was significantly lower in seedlings from seed germinated at ψ ≤ 0.45 MPa.     

Effects of bird ingestion on seed germination of Sorbus commixta

To determine the effects of ingestion by birds on seed germination, we performed germination experiments in the field and laboratory with Sorbus commixta. The germination of four groups of seeds was compared: ingested seeds, seeds defecated in feces after feeding of fruits to birds; extracted seeds, seeds deliberately extracted from the fruit pulp; juiced seeds, seeds plus the juice of the pulp after seeds had been deliberately extracted from the pulp; intact seeds, seeds in untreated intact fruits. In the laboratory, intact and juiced seeds hardly germinated, but ingested and extracted seeds germinated. Thus, the pulp and its juice appeared to inhibit germination, but seeds could germinate without ingestion by birds once the seeds had been manually extracted from the pulp. In the field, intact fruits did not germinate in the first spring, because the seed was still covered with pulp. The pulp of intact seeds decomposed during the first summer, and thus, the seeds had the potential to germinate during the second spring. In fact, most intact seeds do not germinate during the second spring either, since they lose their viability during the first summer. Thus, under natural conditions, most seeds of Sorbus commixta cannot germinate without bird ingestion. Received: 5 July 1997 / Accepted: 7 November 1997     

Effects of flood-influenced factors on seed germination of Ambrosia tenuifolia

Strong fluctuations are exhibited by populations of the perennial herb Ambrosia tenuifolia in the grasslands of the Salado basin (Province of Buenos Aires, Argentina), an area frequently enduring prolonged floods. Flooding causes the death of most dicotyledon plants of the community, A. tenuifolia among them, opening numerous gaps of various sizes. After the recession of the flood the density of A. tenuifolia seedlings was higher in flooded than in non-flooded plots and it was larger in wider gaps. Canopy removal in non-flooded plots increased field seedling emergence of A. tenuifolia up to the levels found in flooded plots. Responses of the seeds in the soil to gap-associated environmental factors such as light quality and temperature regime were studied both in the field and under controlled were studied both in the field and under controlled conditions. Seedling emergence was significantly enhanced when the red:far-red ratio of natural light reaching the soil surface under the canopy of nonflooded plots was increased by means of copper sulfate filters. The influence of light quality and temperature on germination of the soil seed population was also tested using grassland soil monoliths or mesocosms, transported from the field to the laboratory, in which the canopy was clipped and the soil exposed to either red or far-red light and kept at constant or fluctuating temperatures. Significant seedling emergence was observed only when the soil samples were exposed to red light and incubated at alternating temperatures. No emergence was recorded in samples exposed to far-red light or incubated at a constant 25°C. Seeds stored dry in the laboratory were also stimulated to germinate by red light and alternating temperatures but only after dormancy was sufficiently decreased by low temperature stratification or by low temperature under immersion. The results are consistent with the hypothesis that primary dormancy of A. tenuifolia seeds is decreased by low temperatures in winter even if the seeds are submerged as happens when floods occur. The decrease in dormancy makes the seeds prone to be stimulated to germinate by the Pfr form of phytochrome in combination with alternating temperatures. These conditions are likely to be met in the gaps opened by the flood-caused death of dicotyledon plants.     

Effects of osmotic priming and ageing on onion seed germination

Onion seeds were osmotically primed in polyethylene glycol solution (342 g/kg water) either for 14 days before accelerated ageing at 40°C. 18% m.c. for 0, 24, 48, 72 or 96 h, or for 10, 14 or 17 days after ageing. Priming improved the rate of germination compared with non-primed seed. Priming before ageing delayed the loss of viability due to ageing, but priming after ageing had no effect on viability. Primed and dried onion seed was stored for 18 months at 10°C, 9% m.c. with no effect on viability; improvements in germination rate due to priming were maintained over the storage period. Conductivity measurements of seed leachates were not a consistently reliable indicator of germination performance.     

Comparative seed dormancy and germination of eight annual species of ephemeral wetland vegetation in a Mediterranean climate

Ephemeral wetland vegetation (EWV) in the Mediterranean Basin appears in temporary wetlands where favourable hydrological conditions exist only for a short time and year-to-year variability is high. Here, we report results of the seed germination, dormancy and desiccation tolerance of eight annual species living in this vulnerable habitat. Experiments were performed in laboratory conditions under constant and alternating temperatures and using a 12-h daily photoperiod or continuous darkness. Whilst germination and dormancy differed between the species, seeds demonstrated an absolute light requirement and prefer cool temperatures to germinate (mean ≤15 °C). Logistic regression analysis showed significant effects of alternating temperature in all the species except in Tillaea vaillantii whose germination was stimulated by constant temperature. Mean temperature was a significant term in the logistic models for the dormant species Cicendia filiformis, Linum radiola and T. vaillantii for which after-ripening was an effective dormancy-breaking treatment. From these results we infer three strategies of regeneration by seeds: (1) species germinating during the whole vegetative season (2) species germinating in a narrow temperature niche and (3) species requiring flooding (T. vaillantii). Seeds possessed orthodox storage behaviour (tolerating drying to 15 % relative humidity) and may be amenable to seed banking as a means of ex-situ conservation. We conclude that EWV species are adapted to the irregular presence of water with characteristics that are typical of neither truly aquatic nor wetland plants. These EWV species showed a more plastic germination response based on alternating and constant temperature sensitivity and a low proportion of dormant seeds.     

Effects of decadal climate change on zooplankton over the last 50 years in the western subarctic North Pacific

Decadal‐ to multi‐decadal variations have been reported in many regional ecosystems in the North Pacific, resulting in an increasing demand to elucidate the link between long‐term climatic forcing and marine ecosystems. We detected phenological and quantitative changes in the copepod community in response to the decadal climatic variation in the western subarctic North Pacific by analyzing the extensive zooplankton collection taken since the 1950s, the Odate Collection. Copepod species were classified into five seasonal groups depending on the timing of the annual peak in abundance. The abundance of the spring community gradually increased for the period 1960–2002. The spring–summer community also showed an increasing trend in May, but a decadal oscillation pattern of quasi‐30‐year cycles in July. Phenological changes coincided with the climate regime shift in the mid‐1970s, indicated by the Pacific decadal oscillation index (PDO). After the regime shift, the timing of the peak abundance was delayed one month, from March–April to April–May, in the spring community, whereas it peaked earlier, from June–July to May–June, in the spring–summer community, resulting in an overlap of the high productivity period for the two communities in May. Wintertime cooling, followed by rapid summertime warming, was considered to be responsible for delayed initiation and early termination of the productive season after the mid‐1970s. Another phenological shift, quite different from the previous decade, was observed in the mid‐1990s, when warm winters followed by cool summers lengthened the productive season. The results suggest that climatic forcing with different decadal cycles may operate independently during winter–spring and spring–summer to create seasonal and interannual variations in hydrographic conditions; thus, combinations of these seasonal processes may determine the annual biological productivity.     

Prediction of the distribution of Arctic-nesting pink-footed geese under a warmer climate scenario

Global climate change is expected to shift species ranges polewards, with a risk of range contractions and population declines of especially high-Arctic species. We built species distribution models for Svalbard-nesting pink-footed geese to relate their occurrence to environmental and climatic variables, and used the models to predict their distribution under a warmer climate scenario. The most parsimonious model included mean May temperature, the number of frost-free months and the proportion of moist and wet moss-dominated vegetation in the area. The two climate variables are indicators for whether geese can physiologically fulfil the breeding cycle or not and the moss vegetation is an indicator of suitable feeding conditions. Projections of the distribution to warmer climate scenarios propose a large north- and eastward expansion of the potential breeding range on Svalbard even at modest temperature increases (1 and 2 °C increase in summer temperature, respectively). Contrary to recent suggestions regarding future distributions of Arctic wildlife, we predict that warming may lead to a further growth in population size of, at least some, Arctic breeding geese.     

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.     

Exploring the impact of a non-native seed predator on the seed germination of its non-native host

Biological Invasions - Novel interactions between introduced and native species commonly occur and can even be predicted from existing native interactions in a certain area. However, novel...     

Elevational species shifts in a warmer climate are overestimated when based on weather station data

Strong topographic variation interacting with low stature alpine vegetation creates a multitude of micro-habitats poorly represented by common 2 m above the ground meteorological measurements (weather station data). However, the extent to which the actual habitat temperatures in alpine landscapes deviate from meteorological data at different spatial scales has rarely been quantified. In this study, we assessed thermal surface and soil conditions across topographically rich alpine landscapes by thermal imagery and miniature data loggers from regional (2-km²) to plot (1-m²) scale. The data were used to quantify the effects of spatial sampling resolution on current micro-habitat distributions and habitat loss due to climate warming scenarios. Soil temperatures showed substantial variation among slopes (2–3 K) dependent on slope exposure, within slopes (3–4 K) due to micro-topography and within 1-m² plots (1 K) as a result of plant cover effects. A reduction of spatial sampling resolution from 1 × 1 m to 100 × 100 m leads to an underestimation of current habitat diversity by 25% and predicts a six-times higher habitat loss in a 2-K warming scenario. Our results demonstrate that weather station data are unable to reflect the complex thermal patterns of aerodynamically decoupled alpine vegetation at the investigated scales. Thus, the use of interpolated weather station data to describe alpine life conditions without considering the micro-topographically induced thermal mosaic might lead to misinterpretation and inaccurate prediction.     

Potential host colonization by insect herbivores in a warmer climate: a transplant experiment

We conducted a transplant experiment to investigate the potential colonization of a plant species by insect herbivores under a warmer climate. Acacia falcata seeds collected from four latitudes, encompassing the current coastal range of the species (1150 km), were grown in the same soil type and climatic conditions in a glasshouse. Plants were then transplanted to two sites, 280 km north of A. falcata's current coastal range; the transplant sites were 1.2 and 5.5°C warmer than the northernmost and southernmost boundaries of the species' current range, respectively. We compared the structure and composition of the herbivorous Hemiptera and Coleoptera communities on the transplants (i) to that of A. falcata within its current distribution, (ii) to a closely related Acacia species (Acacia leptostachya) that naturally occurred at the transplant sites, and (iii) among the A. falcata transplants originating from seeds collected at different latitudes. Herbivory on A. falcata was also compared between the transplants and the current distribution, and among transplant originating from different latitudes. Thirty species of externally feeding herbivorous Coleoptera and Hemiptera were collected from the transplanted A. falcata over a period of 12 months following transplantation. Guild structure of this herbivore community (based on the proportion of species within each of seven groups based on taxonomy and feeding style) did not significantly differ between the transplants and that found on A. falcata within its natural range, but did differ between the transplants and A. leptostachya. Rates of herbivory did not significantly differ between the transplants and plants at sites within the natural range. There were no significant differences in herbivore species richness or overall rates of herbivory on the transplants originating from different latitudes. In conclusion, host plant identity was apparently more important than climate in influencing the structure of the colonizing herbivore community. If this result holds for other plant–herbivore systems, we might expect that under a warmer climate, broad patterns in insect community structure and rates of herbivory may remain similar to that at present, even though species composition may change substantially.     

镧浸种对水稻种子萌发及幼苗生长的影响

以水稻种子为材料,研究了稀土元素镧对水稻种子活力和幼苗生长的影响。结果表明,1~20mg.L-1La3+处理能提高水稻种子的活力,提高蛋白酶、淀粉酶和脂肪酶的活性,并能促进水稻茎、叶和根系的生长,其中10mg.L-1La3+处理效果最佳。当浓度超过30mg.L-1时,水稻种子萌发和幼苗生长受到抑制。此外,镧对水稻植株地下部分(根系)生长的影响比地上部分(茎叶)生长的影响要明显。镧对水稻种子萌发期间3种酶活性的影响程度表现为蛋白酶>脂肪酶>淀粉酶。     

Effects of temperature,salinity and cold stratification on seed germination in halophytes

Salt tolerance of halophytes corresponds with the habitat requirement of the species. It is an important factor during the germination phase and it can determine successful establishment. This paper presents the effects of alternating temperature–light regimes (4/8°C, 10/20°C, 20/32°C; 12 h dark: 12 h light) and different salinity levels (0, 200, 400, 600 mmol l²¹ NaCl) on seed germination of five halophytes, Halimione pedunculata, Bupleurum tenuissimum, Aster tripolium, Triglochin maritimum and Armeria maritima. The five species differ with respect to family and life‐form and spatially correspond to a decreasing salt gradient (i.e. distance from salt water, with H. pedunculata being the most tolerant and A. maritima being the least). Armeria maritima, A. tripolium and T. maritimum seeds were additionally subjected to a cold stratification experiment. The results showed that Halimione pedunculata, an annual therophyte of year‐round heavily saline habitats, was dormant under all experimental conditions. Bupleurum tenuissimum, a species typical to sites of varying salinity prone to leaching during spring and autumn rainfall, germinated best under cold and warm temperatures, but only under non‐saline conditions. Aster tripolium and T. maritimum, close neighbours in salt marshes, showed very similar germination behaviour: seeds of both species tolerated high levels of salinity and germinated best in summer temperatures during periods of highest soil salinity, and germination was significantly promoted by cold. Armeria maritima, a species usually found on the marginal fringes of saline habitats, germinated only under low salt levels and maximum germination was under cold (spring) and warm (autumn) temperatures, with no significant effect of cold stratification.     

Earlier onset of the spring phytoplankton bloom in lakes of the temperate zone in a warmer climate

The decoupling of trophic interactions is potentially one of the most severe consequences of climate warming. In lakes and oceans the timing of phytoplankton blooms affects competition within the plankton community as well as food–web interactions with zooplankton and fish. Using Upper Lake Constance as an example, we present a model‐based analysis that predicts that in a future warmer climate, the onset of the spring phytoplankton bloom will occur earlier in the year than it does at present. This is a result of the earlier occurrence of the transition from strong to weak vertical mixing in spring, and of the associated earlier onset of stratification. According to our simulations a shift in the timing of phytoplankton growth resulting from a consistently warmer climate will exceed that resulting from a single unusually warm year. The numerical simulations are complemented by a statistical analysis of long‐term data from Upper Lake Constance which demonstrates that oligotrophication has a negligible effect on the timing of phytoplankton growth in spring and that an early onset of the spring phytoplankton bloom is associated with high air temperatures and low wind speeds.     

光照对辽东栎种子萌发和幼苗生长的影响

研究了不同光照梯度[55.4%自然全光照(natural sunlight,NS)、18.9%NS、5.5%NS、2.2%NS、0.5%NS和0.3%NS]对辽东栎种子萌发和幼苗生长的影响.结果表明:辽东栎种子的萌发率和萌发指数在55.4%NS处理达到最大,分别为72.5%和0.22,然后随着光照减弱而逐渐减小,在0.3%NS处理下最小,分别为42.5%和0.11;强光照对种子萌发进程有一定的延迟作用,萌发活力指数随着光照的减弱而增大(0.5%NS处理最大);强光下种子萌发的延迟可能是其对多种命运的权衡性选择.强光照有利于辽东栎幼苗基径和根系生长,以及幼苗干物质的积累,但株高最小(6.06 cm);不同光强处理的辽东栎幼苗具有较大的形态学可塑性,其幼苗阶段对光环境的适应性较强,0.5%NS处理的幼苗比叶面积、比枝长、比根长、叶片叶绿素b含量及叶绿素总量均最大,分别为142.57 cm2.g-1、156.86 cm.g-1、271.87 cm.g-1、0.07 g.cm-2和0.24 g.cm-2,55.4%NS处理下最小,分别为44.89 cm2.g-1、52.84 cm.g-1、101.98 cm.g-1、...