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.     

Germination behaviour of annual plants under changing climatic conditions: separating local and regional environmental effects

The role of local adaptation and factors other than climate in determining extinction probabilities of species under climate change has not been yet explicitly studied. Here we performed a field experiment with annual plants growing along a steep climatic gradient in Israel to isolate climatic effects for local trait expression. The focus trait was seed dormancy, for which many theoretical predictions exist regarding climate-driven optimal germination behaviour. We evaluated how germination is consistent with theory, indicating local adaptation to current and changing climatic conditions, and how it varies among species and between natural and standardised soil conditions. We reciprocally sowed seeds from three or four origins for each of three annual species, Biscutella didyma, Bromus fasciculatus and Hymenocarpos circinnatus, in their home and neighbouring sowing locations along an aridity gradient. Our predictions were: lower germination fraction for seeds from more arid origins, and higher germination at wetter sowing locations for all seed origins. By sowing seeds in both local and standard soil, we separated climatic effects from local conditions. At the arid sowing location, two species supported the prediction of low germination of drier seed origins, but differences between seed origins at the other sites were not substantial. There were no clear rainfall effects on germination. Germination fractions were consistently lower on local soil than on standard soil, indicating the important role of soil type and neighbour conditions for trait expression. Local environmental conditions may override effects of climate and so should be carefully addressed in future studies testing for the potential of species to adapt or plastically respond to climate change.     

Evaluation of global warming effects on the geographical distribution of weeds in paddy fields by characterizing germination time and morphological factors

Global warming, a consequence of climate change, alters rice-paddy ecosystems, especially through the changes of both growth rate of plants and the occurrences of pests, and affects both rice crop production and biodiversity. In this study, factors related to the germination temperatures of 80 weed species in paddy fields were analyzed to elucidate the effect of warming on morphological (leaf size), phenological (germination time), and population (distribution) responses. A self-organizing map (SOM) was used to classify the weed species on the basis of 5 factors related to germination temperature: the minimum, maximum, and optimum temperatures and the minimum and maximum optimal range. Climate data for the Korean Peninsula during 4 different decades (1990s, 2020s, 2050s, and 2080s) were obtained from a regional climate change model following the A1B emission scenario of the Intergovernmental Panel on Climate Change. Changes in the germination time and range of potential habitable areas for the weed species were estimated on the basis of the patterns of the SOM. The species associated with relatively lower germination temperatures tended to have smaller leaves, shorter stems, and earlier flowering and germination times than the species associated with higher germination temperature. The potential germination area increased progressively with rising temperature. The degree of potential increase in germination area was the greatest in the 2080s when the weeds could germinate in most of the southern Korean Peninsula. These results suggest that studying the patterns of germination temperature through SOM could provide necessary information for characterizing the germination of weeds on the basis of various characteristics (e.g., morphology, phenology, and distribution) and would be useful for maintaining agricultural productivity and agroecosystem biodiversity under global warming.     

不同条件下木兰科植物种子的保质期研究

在室温下测定10种木兰科植物种子的储藏时间及在室温、4 ℃、-18 ℃三种温度下测定其中5种木兰科植物种子的储藏时间。结果表明,10种木兰科植物种子在室温条件下的发芽率、发芽势和保存时间均差异较大。5种木兰科植物种子在4 ℃贮藏条件下发芽率最高,发芽率降低最慢,保存时间最长;其次是-18 ℃储藏,室温储藏最差;随着贮藏时间的延长,种子发芽率下降,但发芽所需天数减少,出土整齐度提高,表明其种子具有休眠现象。美丽紫玉兰和深山含笑均在4 ℃下发芽势最高,在室温下次之,在-18 ℃下最差;14 d是5种木兰科植物种子出土萌发最旺盛的时间,不同的温度对种子达到此时间的影响不大,因此,4 ℃低温贮藏和保证高发芽率是提高种子发芽势的有效途径。木兰科植物种子以随采随播的发芽率最高;其萌发前所需休眠时间因种类不同而不同;在不同保存条件下,种子保存时间差别较大。     

Does perianth colour affect the seed germination of two desert shrubs under different storage periods and conditions?

Haloxylon salicornicum and Salsola vermiculata (Amaranthaceae) are two perennial shrubs producing fruits with differently coloured perianths (yellow vs pink) on separate individuals. To test the impact of different storage periods (four, eight and twelve months) and temperature conditions (freezing, room temperature and natural field temperatures) on the seed germination of the two seed categories, germination tests were carried out on both species. For both species, collected from wild plants in the Arabian desert (Qatar), seed germination was tested under two photoperiods (light 12/12; dark 24 hours) at 20/30°C for winged (intact) and de‐winged seeds. For each species, all the considered factors (perianth colour, wing presence, photoperiod, storage period and storage conditions) had significant effects on seed germination (p < 0.001), while the interactions among factors varied in their level of significance depending on the species. In both species, yellow seeds germinated considerably better than the pink ones, the presence of wings slowed the germination, and both storage period and temperature conditions highly influenced their germination ability. Our results indicate that seeds from different perianth colours have different germination strategies to delay their germination and distribute the species through time by escaping germination time by imposing some kind of after‐ripening or seed dormancy. The variation in storage time and storage conditions might help in extending their germination period, where one set of seeds germinate immediately, and the other set of seeds becomes dormant and thus contributes to the formation of a soil seed bank for the long‐term recruitment of seedlings. This study highlights an ecological advantageous strategy for these two species growing in the unpredictable desert habitat.     

Maternal warming affects early life stages of an invasive thistle

Maternal environment can influence plant offspring performance. Understanding maternal environmental effects will help to bridge a key gap in the knowledge of plant life cycles, and provide important insights for species’ responses under climate change. Here we show that maternal warming significantly affected the early life stages of an invasive thistle, Carduus nutans. Seeds produced by plants grown in warmed conditions had higher germination percentages and shorter mean germination times than those produced by plants under ambient conditions; this difference was most evident at suboptimal germination temperatures. Subsequent seedling emergence was also faster with maternal warming, with no cost to seedling emergence percentage and seedling growth. Our results suggest that maternal warming may accelerate the life cycle of this species via enhanced early life‐history stages. These maternal effects on offspring performance, together with the positive responses of the maternal generation, may exacerbate invasions of this species under climate change.     

Germination of Cistus ladanifer seeds in relation to parent material

Variability in seed germination behaviour of Cistus ladanifer L. (rockrose), a Cistaceous species widely distributed in the Mediterranean Basin, was studied in a central Spanish population under controlled conditions. No correlation between seed moisture content and germination was found. Great variability in germination was found among seeds of the population studied, not only between seeds belonging to different mother plants, but also between those collected from different capsules on the same plant. In most cases, seeds preheated at 100 °C for 30 minutes showed a significant increase in germination. This germination behaviour is related to fire regimes as this plant is a typical shrubby element of the mediterranean shrublands. Percent germination did not vary significantly after several months of seed storage at room temperature. In the same way, no difference was found in final germination percentage of seeds stored under room temperature vs. seeds stored under cold conditions.     

Regeneration potential of <Emphasis Type="Italic">Taxodium distichum</Emphasis> swamps and climate change

Seed bank densities respond to factors across local to landscape scales, and therefore, knowledge of these responses may be necessary in forecasting the effects of climate change on the regeneration of species. This study relates the seed bank densities of species of Taxodium distichum swamps to local water regime and regional climate factors at five latitudes across the Mississippi River Alluvial Valley from southern Illinois to Louisiana. In an outdoor nursery setting, the seed banks of twenty-five swamps were exposed to non-flooded (freely drained) or flooded treatments, and the number and species of seeds germinating were recorded from each swamp during one growing season. Based on ANOVA analysis, the majority of dominant species had a higher rate of germination in non-flooded versus flooded treatments. Similarly, an NMS comparison, which considered the local water regime and regional climate of the swamps, found that the species of seeds germinating, almost completely shifted under non-flooded versus flooded treatments. For example, in wetter northern swamps, seeds of Taxodium distichum germinated in non-flooded conditions, but did not germinate from the same seed banks in flooded conditions. In wetter southern swamps, seeds of Eleocharis cellulosa germinated in flooded conditions, but did not germinate in non-flooded conditions. The strong relationship of seed germination and density relationships with local water regime and regional climate variables suggests that the forecasting of climate change effects on swamps and other wetlands needs to consider a variety of interrelated variables to make adequate projections of the regeneration responses of species to climate change. Because regeneration is an important aspect of species maintenance and restoration, climate drying could influence the species distribution of these swamps in the future.      

Effects of seed storage on germination of two succulent desert halophytes with little dormancy and transient seed bank

Seeds of both Salsola imbricata and Haloxylon salicornicum have high germination level and germination speed, and form a transient seed bank in nature. The impacts of storage period and condition on germination level and speed were assessed in the two species. Storage for three months significantly increased both germination level and speed of seeds stored under the different conditions, compared to that of fresh seeds. In both species, nine months storage did not affect germination percentage in cold storage seeds, but completely inhibited it in field seeds. Storage for longer time in room and warm temperatures resulted in significant reduction or complete inhibition in the germination of the two species, so this was more pronounced in H. salicornicum. Storage significantly increased germinate rate index of seeds stored in all conditions till 17 months in S. imbricata and till 12 months in H. salicornicum. In both species, fridge storage had little effects on final germination and germination speed of seeds incubated at the different temperatures, compared to fresh seeds. However, room temperature and warm storages significantly reduced final germination and germination speed at the different temperatures, so the reduction was more pronounced at 35 °C, especially in H. salicornicum.     

假酸浆种子发芽特性研究

在不同温度、不同贮藏时间和方法下,对来源于印度尼西亚的假酸浆种子发芽特性进行研究。结果表明:不同温度对假酸浆种子萌发的影响差异极显著,在15/25℃变温条件下种子发芽率最高,为84.3%,发芽快且整齐;假酸浆种子采收后立即播种其发芽率非常低,室温下贮藏6～9个月时在25℃恒温或15/25℃变温条件下均有较高发芽率,说明假酸浆种子有休眠性,通过延长贮藏时间能打破休眠,促进种子发芽;但室温贮藏15个月后,种子活力下降非常明显。低温冷藏在一定条件下能提高假酸浆种子萌发能力,能延长种子寿命。     

喀什霸王的结实和种子萌发特性

喀什霸王(Zygophyllum kaschgaricum)是生长于中国新疆南部荒漠环境的稀有种及二级保护植物。当前, 该物种在自然种群中呈分散式及片段化分布, 且种群密度低, 种群老龄化较严重。因此, 为了了解该物种种子萌发特性及其对荒漠环境的响应, 该文采用室内控制实验方法, 对该物种的自然坐果率、结籽率、种子吸水特性、种子休眠和萌发特性及对干旱胁迫的响应进行了比较研究。结果表明: 喀什霸王在自然种群中的坐果率及结籽率较低, 且种子的败育率较高。不同干藏时间种子的吸水速率间存在显著差异; 随着干藏时间的延长, 种子的吸水率逐步增强。刚成熟的种子在不同温度及光周期下均可萌发; 其中高温(10/20 ℃, 20/30 ℃)及黑暗条件下的萌发率比低温(10/5 ℃, 5/2 ℃)及光照条件下的萌发率高。不同干藏时间的种子在不同浓度赤霉素(GA₃)下的萌发率均较高; 但低温储藏时间对该物种种子的打破休眠及萌发率没有促进作用。以上结果说明该物种存在非深度生理休眠; 而干藏时间、高温且黑暗及高浓度(50 mmoloL ^-1) GA₃是打破休眠及促进种子萌发的最合适条件。高温条件下的干旱胁迫对喀什霸王种子萌发具有抑制作用; 春季和秋季降水量决定种子的萌发率。总之, 喀什霸王种子在物候上表现出的春秋季萌动及非深度生理休眠以提高幼苗存活力及保障种群稳定性, 是一种对新疆南部干旱及高温胁迫荒漠环境的适应策略。     

中、旱生植物萌发特性及其与种子大小关系的比较

不同生境的植物有不同的生活史对策。该文对分布于河西走廓的42种常见中生植物和22种常见旱生植物种子的萌发特性以及种子大小对萌发能力的影响进行了比较。结果显示,64种植物中最终萌发率超过90%的有9种: 虎尾草(Chloris virgata)、蒲公英(Taraxacum mongolicum)、腺独行菜(Lepidium apetalum)、膜果麻黄(Ephedra przewalskii)、沼生蔊菜(Rorippa islandica)、白草(Pennisetum centrasiaticum)、霸王(Zygophyllum xanthoxylon)、反枝苋(Amaranthus retroflexus)和黑果枸杞(Lycium ruthenicum),占14.06%,其中黑果枸杞、腺独行菜、膜果麻黄、虎尾草的萌发在10 d内完成; 萌发率达到80%~90%的有5种: 毛果群心菜(Cardaria pubescens)、窄叶小苦荬(Ixeridium gramineum)、牛蒡(Arctium lappa)、鞑靼滨藜(Atriplex tatarica)和苣荬菜(Sonchus brachyotus)占7.8%; 萌发率达到60%~80%的有16种,占25%;萌发率在20%~60%的有17种,占26.56%; 萌发率不足20%的有17种: 柠条锦鸡儿(Caragana korshinskii)、野苜蓿(Medicago falcata)、扁蓄(Polygonum aviculare)、苦参(Sophora flavescens)、河西沙拐枣(Calligonum potanini)、白刺(Nitraria tangutorum)、甘草(Glycyrrhiza uralensis)、苦豆子(Sophora alopecuroides)、骆驼蓬(Peganum harmala)、画眉草(Eragrostis pilosa)、多裂骆驼蓬(Peganum multisectum)、老瓜头(Cynanchum komaroviil )、骆驼蒿(Peganum nigellastrum)、田旋花(Convolvulus arvensis)、酸模叶蓼(Polygonum lapathifolium)、卷茎蓼(Polygonum convolvulus)、蝎虎驼蹄瓣(Zygophyllum mucronatum),占25.56%。有26种植物的萌发持续在30 d以上,15种植物在15 d内完成萌发,有31种植物在1~3 d内开始萌发,4种植物在10 d以后才开始萌发。主成分分析和聚类分析显示,中、旱生植物的萌发主要有爆发型、过渡型、缓萌型和低萌型,以过渡型和缓萌型为主;中生植物中萌发率不足20%的有6种,占14.28%, 旱生植物中萌发率不足20%的有11 种,占50%,显示了较多的旱生植物有延迟萌发的行为,这种萌发的延迟及萌发时间的异质性可使物种在不可预测、高死亡风险的环境中仍能确保种的延续。中生植物的种子大小对萌发能力有显著的影响,小种子的物种有较高的萌发率和较快的萌发速率,并且完成萌发所需要的时间较短,而旱生植物的种子萌发不受种子大小的影响。以上结果说明中生植物和旱生植物长期适应于不同的湿、旱生环境,在不同的选择压力下,生活史对策也出现了较明显的差异。     

冷层积和室温干燥贮藏对河西走廊8种荒漠植物种子萌发的影响

不同贮藏和处理条件对不同植物的种子萌发有不同的影响。该文以河西走廊干旱半干旱区8种荒漠植物为研究对象, 探讨了种子经历不同冷层积(4 ℃、-5 ℃、-26 - 10 ℃)和室温干燥贮藏后的萌发响应。研究结果表明: 1)冷层积可使种子萌发率提高、保持不变或降低, 冷层积的有效温度下界可降至-5 ℃或更低。4 ℃和-5 ℃的冷层积使多裂骆驼蓬(Peganum multisectum)和驼蹄瓣(Zygophyllum fabago)种子的萌发率升高、萌发速度加快, 冬季过低的气温以及较大的温度变幅(-26 - 10 ℃)使部分种子萌发率升高。3种冷层积和室温干燥贮藏使黑果枸杞(Lycium ruthenicum)种子萌发率达到90%-100%。唐古特白刺(Nitraria tangutorum)、甘草(Glycyrrhiza uralensis)、苦马豆(Sphaerophysa salsula)种子经过3种冷层积和室温干燥贮藏后萌发率变化较小。中亚紫菀木(Asterothamnus centrali-asiaticus)种子对各种贮藏条件的响应不明显, 部分种子活性丢失。刺沙蓬(Salsola ruthenica)种子扩散时有较高的萌发率(84%), 经-5 ℃和-26 - 10 ℃冷贮藏后, 种子仍具有较高的萌发率, 经4 ℃冷贮藏后几乎不萌发, 大部分种子活性丢失。2)不同物种的种子经过不同方式的贮藏后, 萌发对温度的响应不同。经冷层积后的多裂骆驼蓬种子萌发响应于恒温, 驼蹄瓣和刺沙蓬种子萌发更加响应于变温条件; 多数植物种子在变温培养下萌发速度慢于恒温下。     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

Temperature controls seed germination and dormancy in the European woodland herbaceous perennial Erythronium dens-canis (Liliaceae)

We examined the germination ecology and the temperature requirements for germination of Erythronium dens-canis, under both outdoor and laboratory conditions. E. dens-canis is a spring flowering woodland geophyte widely distributed across Europe. Germination phenology, including embryo development and radicle and cotyledon emergence, were investigated in a natural population growing in Northern Italy. Immediately after harvest, seeds of E. dens-canis were either sown on agar in the laboratory under simulated seasonal temperatures or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of seed dispersal, grew during summer and autumn conditions in the laboratory and in the wild, culminating in radicle emergence in winter when temperatures fell to ≈ 5 °C. Emergence of cotyledons did not occur immediately after radicle emergence, but was delayed until the end of winter. Laboratory experiments showed that temperature is the main factor controlling dormancy and germination, with seeds becoming non-dormant only when given warmth, followed by cold stratification. Unlike seeds of E. dens-canis that germinate in winter, in other Erythronium species radicle emergence occurs in autumn, while in some it is delayed until seeds are transferred from winter to spring conditions. Our results suggest that there is genetic and environmental control of the expression of seed dormancy amongst Erythronium species, which is related to local climate.     

Increasing temperatures can improve seedling establishment in arid-adapted savanna trees

Plant species are shifting their ranges in response to global climate change, thus intensifying the need to predict such changes accurately. As the environmental requirements controlling plant distribution act differently at each developmental stage, there is a need to acquire a demographic-specific understanding of the factors which determine these distributions. Here we investigated the germination niche of two common savanna species Acacia nigrescens and Colophospermum mopane, with the aims to disentangle the direct and indirect effects of temperature on seed germination and establishment and to explore the impact of higher temperatures on the establishment success of savanna trees. Under laboratory conditions, we used thermal gradient plates to determine the thermal germination niche of both species, and a water stress experiment was conducted on C. mopane to account for water–temperature interactions. Using these data we parameterised a soil-moisture model to determine germination and establishment success under field conditions at current and future temperatures (+4 °C). Based on this model, higher future temperatures will not limit germination directly, but they will reduce the number of germination events by reducing the time window of suitable available soil water. Conversely, warmer conditions will accelerate the rate of radicle extension and increase the frequency of seedling establishment events. An additional advantage of higher temperatures is that fewer seeds will germinate, resulting in slower seed bank depletion when successful seedling establishment events do occur.     

Seed bank of seasonally flooded grassland: experimental simulation of flood and post-flood

Wetland seed banks comprise the propagules of plant species that have species-specific germination requirements for germination in either flooded or dry conditions. At the community level, wetland structure and succession during and after a seasonal flooding event depends upon the early life-history requirements of species, including germination under flooded and dry conditions. We examined the effects of simulated flood and post-flood scenarios on seedling emergence from a seed bank of seasonally flooded grassland in the Pantanal, Brazil. Field samplings were conducted in both wet and dry seasons, both of which were subject to flood and post-flood conditions. A total of 70 species emerged from the seed bank, dominated by Poaceae and Cyperaceae. Sixteen species were exclusive to the wet and one exclusive to the dry season. The richness of perennial species was higher under flood conditions, while the richness of annuals was greater post-flood. In general, the aquatic and amphibious species exhibited a significant germination response to flooding. Terrestrial species only germinated in post-flood conditions, with higher richness in the dry season. Four species had high seedling abundance in both treatments. The capacity of regeneration by seeds is high in these grasslands and can be increased by seasonal flooding and drawdown. In these seasonally flooded grasslands, we observed three main germination strategies: under flooded conditions, aquatic and amphibious species; post-flood conditions, an explosion of annual amphibious and terrestrial species; and in moist soil, perennial terrestrial species. The differential responses to flooding versus post-flood conditions help to maintain the structure and species richness in the community over time.     

Modelling the germination of Stellaria media using the concept of hydrothermal time

The germination characteristics of Stellaria media (common chickweed) were investigated over a range of constant temperatures and degrees of moisture stress in order to assess the suitability of hydrothermal time as a basis for modelling germination under field conditions. Maximum percentage germination occurred over a much narrower temperature range around the optimum temperature than previously seen for cultivated crop seed. The entire final percentage germination response to temperature in water was well described by two probit curves, and this model was extended to describe the data at all water potentials at a temperature close to the optimum. The implications of the reduction in germination at nonoptimal temperatures are discussed with respect to the interpretation of germination progress curves and conditional dormancy. After adjusting for maximum percentage germination, a hydrothermal time model was found to fit the data set well within the conditions normally encountered in horticultural seedbeds. This separation of the final percentage germination presents a flexible modelling approach that allows for the different levels of dormancy typically expressed within weed populations. By contrast with many previously reported species, S. media had a synchronous germination rate within the population at any given temperature/water potential combination. This synchronous germination of at least a proportion of the population over a wide range of temperature and water potentials might have ecological significance for the opportunistic germination behaviour of this weed species.     

温带半干旱地区一年生植物种子的萌发特性

在实验室条件下研究了中国温带半干旱地区科尔沁沙地的23种1年生植物的种子萌发特性（新采集种子、冷藏和干藏种子）.大籽蒿、虎尾草、冠芒草、沙蓬和地锦的新种子萌发率达90%左右,11种植物新种子萌发率均低于70%,说明这些植物的新种子具有或多或少的休眠属性.经过150d的冷干藏后,大籽蒿、虎尾草萌发率保持在90%以上,说明这两种植物完全没有休眠机制;冠芒草、沙蓬和地锦的种子萌发率下降较多,可能是储藏的环境条件导致的2次休眠现象;冷藏和干藏处理均能使绿珠藜、毛马唐、细叶益母草、雾冰藜、金狗尾草、苋菜、马齿苋、碱地肤和水稗草的种子在生长季开始时完成生理后熟,萌发率达到80%以上;干藏有利于促进毛马唐、细叶益母草、马齿苋和鹤虱的种子成熟,冷藏有利于促进绿珠藜和金狗尾草的种子成熟;黄蒿、灰绿藜、画眉草和烛台虫实在不同处理下的萌发率都比较低,说明种子内在生理休眠作用较强,具有减少种子一次性萌发数量的风险分摊策略.大多数1年生植物均能在较短时间内达到最终萌发率的90%,表现出迅速萌发的特性;黄蒿、灰绿藜、碱地肤和沙蓬种子则在不同处理中表现出延长萌发时间的策略来适应半干旱地区不确定的环境条件.最后,探讨了几种主要1年生植物的种子萌发对策与其对环境适应机制之间的关系.     

Seed germination of high mountain Mediterranean species: altitudinal,interpopulation and interannual variability

The germination response of 20 species from high altitude Mediterranean climates, most of them rare endemics, was studied. Our main goal was to model the germination response of a complete set of Iberian high mountain species. The effect of temperature and other parameters, such as spatial and temporal short gradients, on germination were also evaluated. Some seed features (mass and size) were also related to the germination response. Finally, we tested the effect of cold-wet stratification pretreatment when germination was low under natural conditions. Seeds were collected at four locations from 1,900 to 2,400 m a.s.l. in the Sierra de Guadarrama (Spanish Central Range) over two consecutive growing seasons (2001–2002) and submitted to different temperatures and a constant photoperiod of 16 h light/8 h darkness. Most plants readily germinate without treatment, reaching an optimum at relatively high temperatures in contrast to lowland Mediterranean species. Seeds seem to be physiologically prepared for rapid germination even though these plants usually face very intense summer droughts after ripening and dispersal. Germination was also highly variable among altitudes, populations and years, but results were inconsistent among species. Such flexibility could be interpreted as an efficient survival strategy for species growing under unpredictable environments, such as the Mediterranean climate. Finally cold-wet stratification increased germination capacity in five of nine dormant species, as widely reported for many arctic, boreal and alpine species. In conclusion, high mountain Mediterranean species do not differ from alpine species except that a relatively high number of species are ready to germinate without any treatment.