Time of germination and establishment success after fire of three obligate seeders in a Mediterranean shrubland of central Spain

Aim Determining how differences in time of germination can affect plant establishment in plant communities that, after a disturbance, must reestablish from seeds under climatic conditions subject to extremes, such as the Mediterranean. Although early germination may be beneficial for survival in summer, when drought is severe, this may expose the seedlings to winter extremes, thus to higher mortality. Understanding how sensitive is the establishment of different species to temporal patterns of germination will help to understand the factors that control species distribution and community stability in disturbance‐prone environments, as well as its sensitivity to changes in weather patterns as climate changes. Methods An experimental fire was made in early fall in an old Cistus–Erica shrubland in Toledo (central Spain). After fire, germination, survival and growth of the three dominant seeder species (Cistus ladanifer, Erica umbellata and Rosmarinus officinalis) were monitored during the first 3 years after fire. Seedlings were tagged to identify their time of emergence, and divided into cohorts according to their month of germination. Differences in survival of the various cohorts were evaluated by means of a Wilcoxon (Gehan) statistic. Height of surviving, tagged plants was compared among cohorts by means of a Kolmogorov–Smirnov test. Results The year following fire was one of the driest on record, while the next one was one of the wettest. Germination was more abundant during the first than during the second year. Establishment was mainly from first‐year germination, as the majority of second‐year germinated seedlings died. Temporal patterns of germination within a year and between years varied between species. Seedling mortality was highest immediately following germination, not in summer. Mortality was related to time of germination: during a given period of time, the mortality of younger seedlings was higher than that of older ones. However, survival was not highest for the first cohorts. In general, the earlier the seedlings germinated the more vigourous they became, more clearly so for Cistus than for Rosmarinus, but differences tended to disappear with time. Overall, time of germination varied between species and affected differently seedling survival and vigour of the various species. Rosmarinus and Cistus had sufficient survivors to reestablish the initial population. Erica, despite abundant germination, suffered a strong population reduction. Main conclusions Mediterranean shrub species differ in their temporal patterns of germination and survival after fire. The effect of time of germination is complex: germinating early is advantageous since old seedlings fared better than younger ones when confronted with the same rigours. However, germinating early might expose the seedlings to greater hazards and the first cohort might not survive best. The temporal window for establishment is narrow and mainly restricted to the first year after fire. Second year seedlings, irrespective of most favourable conditions, survived very little. Missing the window of establishment might virtually lead to a population collapse, despite having very high germination, as found for Erica.     

Size-dependent perennation bud formation and its effect on seedling establishment inVeronicastrum sibiricum ssp.japonicum

Seedling establishment of a perennial,Veronicastrum sibiricum ssp.japonicum colonizing at 1,600 m altitude in Nikko National Park was studied for two years. About half of the first-year seedlings died during the growing season and 45–74 per cent of the seedlings surviving the first summer died during the following winter season. This winter mortality depended on the end-of-season size of the seedling in the previous autumn and was caused mainly by the absence of perennation buds. Seedlings which had emerged on bare ground attained larger size and had higher winter survival than seedlings in a mat of moss. Seedlings germinating in early season attained larger size and had higher probability of winter survival than seedlings germinating in later season.     

亚热带中山常绿阔叶林木本植物幼苗数量动态及其与生境的相关性

以百山祖自然保护区5 hm2永久样地150个幼苗监测站木本植物幼苗为研究对象,2008—2011年定期调查样方中幼苗的种类、数量、萌发、死亡等,探究亚热带中山常绿阔叶林幼苗种类组成、数量动态及其与生境的相关性。结果表明:1)百山祖样地在2008年至2011年出现的幼苗属于26科,40属,共53个物种,不同物种萌发时段有异;2)2009年样地幼苗存活比率为7.7%,2010年为-20.8%,2011年则是-0.3%,幼苗存活比率不高,种类和数量呈减少趋势;3)存活幼苗中有明显的优势物种,分别为光亮山矾(Symplocos lucida)、尖连蕊茶(Camellia cuspidata)、浙闽新木姜子(Neolitsea aurata var.undulatula)、尖叶菝葜(Smilax arisanensis)和短尾柯(Lithocarpus brevicaudatus),5个物种之和占幼苗总数比例50%;4)种子的萌发与生境有极显著的相关性,且与生境因子中水分关联最大;5)存活幼苗数与样站坡位、水分、落叶层厚度呈现显著相关性,水和光照是影响幼苗存活的主要因素。     

Localization and Activity of Naphthylamidases in Germinating Seeds of Scots Pine, Pinus sylvestris

Extracts prepared from endosperms of germinating seeds of Scots pine, Pinus sylvestris L., rapidly hydrolysed the β-naphthylamides of L-phenylalanine and L-leucine optimally at pH 6.5 and that of L-arginine at pH 7.7. Disc electrophoresis followed by activity staining showed that the activities were due to two naphthylamidases (aminopeptidases) with different substrate specificities. Seeds were allowed to germinate at 20°C on agar gel in the dark and the activities on the three substrates were assayed from separated endosperms and seedlings at various stages of germination. The activities in the endosperm of resting seeds were relatively high and they remained unchanged throughout the period of reserve protein mobilization (seedling length up to 50 mm), after which they began to decrease. The activities of the naphthylamidases are rather small compared with those of the two alkaline peptidases of pine, contributing about 17% of the total amino-peptidase activity in the endosperm of germinating seeds. The total aminopeptidase activity is sufficient to account for the rate of storage protein mobilization during germination. In the seedlings the naphthylamidase activities (per seedling) increased continuously during germination, and activities per g dry weight were higher than those in the endosperm.     

A study of the relationship between seedling characters and rate of germination within a seed lot

The relationship between seedling characters and germination rate within a seed lot was studied in cauliflower, leek and onion seeds. Newly germinated seeds were selected after successive days of imbibition at 20°C and placed on slope tests to assess early seedling growth. In all three species seedling length decreased and the coefficient of variation of those seedling lengths increased with increasing number of days of imbibition required for germination. Slow germinating seeds in all three species produced fewer normal healthy seedlings than faster germinating seeds. The relevance of these results to pre-germinated seed sowing techniques is discussed.     

The development of seedlings from fragments of monoembryonic seeds as an important survival strategy for Eugenia (Myrtaceae) tree species

The uncommon ability of monoembryonic seeds of Eugenia to develop seedlings after cutting or even after the removal of more than half of their storage tissue has recently been reported. Some Eugenia species are included among those at risk of disappearing, so the regeneration of plantlets from fragments of seeds could be an important mechanism both for the production of more than one normal seedling per seed and to understand the survival strategies of these species. Because the period in which this ability is present has not been studied, we analyzed the regenerative capacity of seeds of five Brazilian native species of Eugenia, considering two levels of maturity and three germination phases. Mature seeds have a greater potential to regenerate than immature ones; germinating seeds showed that the longer the root protrusion, the smaller the potential to regenerate new seedlings. However, our results clearly demonstrate that the ability to regenerate new roots or complete seedlings is present during a long period from the beginning of development until the late phases of germination. Cutting is potentially important to obtain plants on a larger scale. Because of intense predation of these seeds, this ability could be linked to an essential strategy for survival even after the removal of more than half of the storage tissues. As an alternative strategy to orthodox seeds, whose preservation is based on tolerance to desiccation, the recalcitrant seeds of Eugenia probably adopted the great reserve quantity and the regenerative capacity, allowing them to undergo successive germinations.     

Effects of deer,mice and dwarf bamboo on the emergence,survival and growth of <Emphasis Type="Italic">Abies homolepis</Emphasis> (Piceaceae) seedlings

In the subalpine mixed forest of Mt. Ôdaigahara, mid-western Japan, the understory is dominated by dwarf bamboo (Sasa nipponica), which is the major forage of overly populous sika deer (Cervus nippon). In the present study, we monitored the survival and growth of Abies homolepis seedlings over 5years to determine how they responded to the experimental removal of dwarf bamboo and to the exclusion of sika deer and mice (Apodemus argenteus and A.speciosus). Deer and dwarf bamboo reduced the survival of seedlings but had different effects on growth. The stems of seedlings were shorter in the presence of deer, indicating that taller seedlings were apt to be browsed by deer, whereas the diameters of seedlings were smaller in the presence of dwarf bamboo, mainly owing to its shading effect. The presence of mice decreased the number of seedlings germinating in a particular site, but had no effect on seedling survival after germination. There was no significant indirect effect whereby the survival of seedlings was predicted to be facilitated by the decreased biomass of bamboo because of grazing by deer. We supposed that this might be because the direct negative effect of deer was so large as to conceal the positive indirect effect.     

Conflicting selection on the timing of germination in a natural population of Arabidopsis thaliana

The timing of germination is a key life‐history trait that may strongly influence plant fitness and that sets the stage for selection on traits expressed later in the life cycle. In seasonal environments, the period favourable for germination and the total length of the growing season are limited. The optimal timing of germination may therefore be governed by conflicting selection through survival and fecundity. We conducted a field experiment to examine the effects of timing of germination on survival, fecundity and overall fitness in a natural population of the annual herb Arabidopsis thaliana in north‐central Sweden. Seedlings were transplanted at three different times in late summer and in autumn covering the period of seed germination in the study population. Early germination was associated with low seedling survival, but also with high survival and fecundity among established plants. The advantages of germinating early more than balanced the disadvantage and selection favoured early germination. The results suggest that low survival among early germinating seeds is the main force opposing the evolution of earlier germination and that the optimal timing of germination should vary in space and time as a function of the direction and strength of selection acting during different life‐history stages.     

The effect of the etched (et) mutation on the amylolytic enzyme activities in germinating kernels and seedlings of Zea mays

Summary The etched (et) mutation in maize causes distinct depressions and structural gaps in the endosperm and also gives rise to virescent seedlings, - and -Amylase activities were observed to be higher in et ⁺ et ⁺ kernels and seedlings as compared to that of the et et mutant. The total amylase and -amylase trends during germination also differed between normal and mutant kernels and seedlings (it increases in the wildtype and decreases in et et). On the contrary, the overall -amylase trend was found to be similar in both genotypes (slight decrease during germination). The native gel electrophoresis of crude enzyme extracts did not reveal any qualitative differences in and amylases during germination. The germinating et et kernels initially showed lower levels of starch compared with the wild type kernels, whereas no such difference was found at later stages of germination. It is concluded that et gene associated endosperm lesions lead to an impairment of starch degradation in germinating kernels resulting in virescent seedlings.     

Density-dependent germination and the role of seed leachate

Abstract While density dependence is a central issue in much of plant ecology, it is often overlooked during the crucial seed germination period of the plant life-cycle. Here, patterns of germination in relation to initial seed density for 12 phylogenetically-diverse perennial plant species are described from laboratory experiments. When each of the 12 species was analysed individually, seeds of Alysicarpus rugosus, Callistemon citrinus, Eragrostis curvula and Panicum miliaceum showed a significant decrease in the proportion of seeds germinating at high densities of conspecifics. A meta-analysis carried out by grouping 11 of the 12 species together revealed an overall significant effect for a decrease in the proportion of seeds germinating at high conspecific densities compared with low con-specific densities. Significant decreases in the proportion of seeds germinating are interpreted as risk reappraisal by seeds through dormancy in response to potentially hazardous conditions imposed by high density clusters of seeds all germinating at once. The four species that responded significantly to high densities individually were each treated at low densities with a leachate solution obtained from high density conspecifics. For Alysicarpus rugosus and Panicum miliaceum, this resulted in a significant decrease in the proportion of seeds germinating at simulated high densities implicating the leachate as a causative agent. Heterospecific effects were investigated similarly for A. rugosus and E. curvula by the addition of leachate from high density clusters of seeds of one species upon the other. Only A. rugosus decreased germination significantly through the addition of leachate. These results demonstrate the ability of seeds to predict environmental conditions of the habitat into which they will emerge in terms of potential competitive interactions from neighbouring seedlings.     

Drought tolerance of germinating seeds and young seedlings of Anastatica hierochuntica L.

Summary Drought tolerance of germinating seeds and young seedlings of Anastatica hierochuntica L. was studied under controlled conditions. When seeds at various stages of germination were air-dried, or alternatively were desiccated over CaCl₂ to the same or a lower water level than in the air-dried seeds, and after various periods of storage were rewetted, they readily continued germination or growth. Similarly, 60% of dried young seedlings with rootlets 4–6 mm long that had been dehydrated for one week, renewed their growth 8 h after wetting, their shrivelled, dried rootlets imbibing water. Recovery was adversely affected by both longer periods of germination prior to the dehydration, or by the longer duration of storage of the redried seeds/seedlings. The higher rate of dehydration also reduced recovery. It is argued that despite this tolerance of seedlings to drought, the Rose of Jericho cannot be considered a resurrection plant. Compared with other desert annuals, this behavior is specific for Anastatica. However, it may occur also in other annual species of populations sequestered within the driest of desert habitats.     

华南青刚坚果的萌发和育苗

华南青刚（壳斗科）Ｃｙｃｌｏｂａｌａｎｏｐｓｉｓ ｅｄｉｔｈａｅ（Ｓｋａｎ）Ｓｃｈｏｔｔ的坚果，分别以３种不同的位置（平放、柱座向上及桩座向下）埋进泥土，测试不同位置对种发芽率及幼苗成长的影响。结果显示坚果平放的发芽率最高，幼苗生长亦最快。还就实验结果对苗圃期发育苗的技术作出了讨论。     

Mechanisms of structural change derived from patterns of seedling emergence and mortality in a semi-natural meadow

Questions: Is seedling emergence limited by the set of viable seeds, by incompatibility between the phenology of seed shedding and timing of mowing, or by dry weather in germination periods? Does seedling mortality fluctuate with season and weather? Location: Negrentino, southern Alps, Switzerland. Methods: Fecundity estimates of the dominant grass Bromus erectus; highly frequent counts of spontaneous seedlings by species and calculation of a community-level average mortality rate across 5 years; species-level records of seed shedding date and measurements of seed mass; measurement of soil moisture. Results: B. erectus produced 143.9 viable seeds/m²/year while the density of its seedlings was a 55 times smaller fraction. Grasses had fewer seedlings than forbs and their phenology of seed shedding was less compatible with mowing date. Soil moisture was a strong determinant of seedling emergence in spring and less so in autumn. Average seedling mortality declined with age of the populations and reached a maximum in an extremely dry summer. In relatively wet summers establishment success was positively related to seed mass. Conclusion: Community structure is susceptible to drought through mechanisms that selectively reduce recruits of coexisting plant functional groups. We propose that (1) more frequent intense droughts tend to reduce species that depend on frequent recruitment from seed, hence favour long-lived clonally spreading species, (2) drought timing selects between species with different germination phenology and drought resistance, and (3) drought impacts can be mitigated by changing management regimes that affect seed shedding.     

Specificity of fungal associations of Pyroleae and Monotropa hypopitys during germination and seedling development

Mycoheterotrophic plants obtain organic carbon from associated mycorrhizal fungi, fully or partially. Angiosperms with this form of nutrition possess exceptionally small ‘dust seeds’ which after germination develop ‘seedlings’ that remain subterranean for several years, fully dependent on fungi for supply of carbon. Mycoheterotrophs which as adults have photosynthesis thus develop from full to partial mycoheterotrophy, or autotrophy, during ontogeny. Mycoheterotrophic plants may represent a gradient of variation in a parasitism–mutualism continuum, both among and within species. Previous studies on plant–fungal associations in mycoheterotrophs have focused on either germination or the adult life stages of the plant. Much less is known about the fungal associations during development of the subterranean seedlings. We investigated germination and seedling development and the diversity of fungi associated with germinating seeds and subterranean seedlings (juveniles) in five Monotropoideae (Ericaceae) species, the full mycoheterotroph Monotropa hypopitys and the putatively partial mycoheterotrophs Pyrola chlorantha, P. rotundifolia, Moneses uniflora and Chimaphila umbellata. Seedlings retrieved from seed sowing experiments in the field were used to examine diversity of fungal associates, using pyrosequencing analysis of ITS2 region for fungal identification. The investigated species varied with regard to germination, seedling development and diversity of associated fungi during juvenile ontogeny. Results suggest that fungal host specificity increases during juvenile ontogeny, most pronounced in the fully mycoheterotrophic species, but a narrowing of fungal associates was found also in two partially mycoheterotrophic species. We suggest that variation in specificity of associated fungi during seedling ontogeny in mycoheterotrophs represents ongoing evolution along a parasitism–mutualism continuum.     

The role of invertebrates in seedling establishment in a heterocarpic plant,Atriplex sagittata

Seed heteromorphism is a marked character of many Chenopodioideae (Amaranthaceae). Seed morphs differ in dormancy, germination and seedling biology, but differences in their predation have not yet been studied. Atriplex sagittata produces small black dormant and large brown non‐dormant seeds. In this study, the timing of seed release and seedling establishment were ascertained, and their consumption by invertebrates (carabids, isopods and slugs) was studied. Seeds dispersed in the autumn passed the winter on the ground surface, protected from invertebrate predation by low temperatures. In the following vegetative season, ungerminated black seeds exposed to predation on ground surface were preferred by a large carabid species, Pseudoophonus rufipes. Some black and all brown seeds escaped predation by germinating in early spring. The seedlings were little endangered by carabids and isopods but were preferred by an invasive slug, Arion vulgaris, the feeding of which can exterminate seedlings at places in which slugs are abundant. Invertebrate predation is important factor of seed and seedling mortality of A. sagittata and seed heteromorphism modifies its intensity and timing.     

外源5-氨基乙酰丙酸对盐胁迫下菘蓝种子萌发及幼苗抗氧化酶活性的影响

采用砂培方式,研究了外源5-氨基乙酰丙酸(ALA)对盐胁迫下菘蓝种子的萌发、幼苗叶片的可溶性糖含量、丙二醛(MDA)含量及其抗氧化酶活性的影响,探讨ALA缓解菘蓝受盐胁迫伤害的响应机制。结果显示:(1)菘蓝种子萌发及幼苗生长在100 mmol·L^-1 NaCl胁迫下受到明显的抑制,种子发芽率、发芽势、发芽指数、活力指数与自然含水量均显著降低,丙二醛含量、可溶性糖含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)活性显著升高。(2)盐胁迫下适宜浓度的ALA处理显著提高了种子萌发率、自然含水量及SOD、POD和CAT活性,降低了可溶性糖和丙二醛的含量,并以16.7 mg·L^-1 ALA处理盐胁迫下菘蓝种子的发芽率、发芽势最大,其幼苗的SOD、POD、CAT活性最强。研究表明,盐胁迫显著抑制菘蓝种子的萌发及幼苗生长,适宜浓度的ALA能够有效缓解盐胁迫对菘蓝种子萌发及幼苗生长的伤害,提高植株的抗盐性,并以16.7 mg·L^-1 ALA处理效果最佳。     

Tree seed germination and seedling establishment in treefall gaps and understorey in a subtropical forest of northeast India

Abstract Seed germination, and survival and growth of seedlings of four dominant tree species, Quercus dealbata, Quercus griffithii, Quercus glauca and Schima khasiana were studied in the treefall gaps and forest understorey of an undisturbed mature-phase humid subtropical broadleaved forest in northeast India. Three important microenvironmental factors namely photosynthetically active radiation (PAR), soil moisture and litter depth, were also measured in the forest understorey and gaps and correlated with seedling mortality. Seed germination of S. khasiana was significantly higher in the treefall gaps than in the understorey; among the tree species studied, it had the highest germination. Quercus seedlings were abundant in the understorey and small gaps, while S. khasiana seedlings were more numerous in the large gaps. The survivorship curves for the seedling populations revealed that the three Quercus species survived better in the understorey, while S. khasiana did so in the gaps. PAR and soil moisture were positively correlated with tree seedling mortality, which occurred mainly during the winter months. The Quercus seedlings grew better in the forest understorey and small gaps and S. khasiana seedlings in the large gaps. The differential performance of the tree seedlings to the conditions prevailing in the understorey and gaps of two sizes indicates that different species were adapted to different light environments depending upon their optimum requirements. This could be an effective mechanism for promoting species coexistence in the forest community.     

Assessing context-dependent survival of <Emphasis Type="Italic">Quercus glauca</Emphasis> seeds in a humid maritime woodland

Whilst consumption by rodents is often invoked as a major mortality factor for large-seed species of trees, its relative importance compared with other mortality factors is poorly known. We investigated experimentally the fate of post-dispersal seeds of Quercus glauca under different understorey environments (areas covered by (i) a pteridophyte Pyrrosia lingua, (ii) a ground-vine, Trachelospermum asiaticum and (iii) no vegetation) from the germination stage to seedling emergence and establishment stages in humid maritime woodland. We employed a pair of caged and uncaged treatments to evaluate the impact of seed removal/predation by rodents, which allowed us to separate seed removal/predation mortality from mortality due to other factors. Effects by rodents were greater in the no-understorey habitat than in the Pyrrosia and Trachelospermum habitats at early stages of development, whilst non-rodent-associated mortality was relatively more important towards the seedling establishment stages in all habitats. In the absence of predation/removal by rodents (i.e. the caged treatment), more seedlings survived in the no-understorey habitat whilst seedlings were significantly taller in the Pyrrosia habitat. In contrast, no significant difference was observed in either seed/seedling survivorship or seedling height amongst habitats where seeds/seedlings were exposed to rodent predation/removal. Overall, this study in a humid maritime woodland has revealed the temporally variable influence of mortality factors and the context-dependent survival of oak seeds/seedlings, making a contrast to observations in drier woodlands; in the no-understorey environment predation/removal effect was heavier but later survivorship was higher, whilst in vegetated environments, predation/removal was reduced but survivorship was not high.     

Mechanisms associated with tolerance to flooding during germination and early seedling growth in rice (Oryza sativa)

Background and Aims

Flooding slows seed germination, imposes fatalities and delays seedling establishment in direct-seeded rice. This study describes responses of contrasting rice genotypes subjected to flooding or low oxygen stress during germination and discusses the basis of tolerance shown by certain cultivars.

Methods

In one set of experiments, dry seeds were sown in soil and either watered normally or flooded with 10 cm of water. Seedling survival and shoot and root growth were assessed and seed portions of germinating seedlings were assayed for soluble sugars and starch concentrations. The whole germinating seedlings were assayed for amylase and peroxidase activities and for ethylene production. Activities of enzymes associated with anaerobic respiration were examined and gene expression was analysed separately with seeds germinating under different amounts of dissolved oxygen in dilute agar.

Key Results

Flooding during germination reduced survival but to a lesser extent in tolerant genotypes. Starch concentration in germinating seeds decreased while sugar concentration increased under flooding, but more so in tolerant genotypes. Amylase activity correlated positively with elongation (r = 0·85 for shoot and 0·83 for root length) and with plant survival (r = 0·92). Tolerant genotypes had higher amylase activity and higher RAmy3D gene expression. Ethylene was not detected in seeds within 2 d after sowing, but increased thereafter, with a greater increase in tolerant genotypes starting 3 d after sowing. Peroxidase activity was higher in germinating seeds of sensitive genotypes and correlated negatively with survival.

Conclusions

Under low oxygen stress, tolerant genotypes germinate, grow faster and more seedlings survive. They maintain their ability to use stored starch reserves through higher amylase activity and anaerobic respiration, have higher rates of ethylene production and lower peroxidase activity as germinating seeds and as seedlings. Relevance of these traits to tolerance of flooding during germination and early growth is discussed.Key words: Amylase, anoxia, crop establishment, direct-seeded rice, ethylene, flooding, germination, hypoxia, Oryza sativa     

Germination and establishment of Sahelian rangeland species

Summary In order to understand the vegetation dynamics of Sahelian rangelands, the effects of water availability on germination were investigated under controlled conditions in climate rooms. Mixtures of seeds from species that occur in the same habitats but have different seed characteristics were exposed to different watering treatments. Responses to the treatments in the climate room were comparable to those observed in the field situation. However, induction time was generally some-what longer, and in some cases the germination rate was lower. The size, frequency, and timing of showers decisively influenced the ratio between the proportions of the various species among the seedlings that established. In general, conditions were favourable for fast germinating species with rainfall patterns without serious intermittent periods of drought, whereas the conditions became favourable for the slower germinating species after dry periods had eliminated the seedlings of the fast germinating species. Large differences in drought resistance were found among seedlings of different species. This causes more differentiation in establishment of species. Seed losses during the pre-emergence phase were also important. These losses can be very high, especially for the fastest germinating species. The dynamics observed in field situations could be explained on the basis of germination characteristics and drought resistance.