温度对高山植物紫花针茅种子萌发特性的影响

温度是影响种子萌发的重要因子,在气候变暖和草地退化的背景下,认识温度变化对紫花针茅（Stipa purpurea） 种子萌发的影响有重要意义。作者系统研究了6个恒温条件（5、10、15、20、25、30℃）和3个变温条件（5/15、10/20、15/25℃）对不同居群紫花针茅种子萌发特性的影响。结果表明,紫花针茅种子适宜的萌发温度范围为15~25℃,低于10℃或高于30℃的温度都会抑制种子的萌发;与对应的恒温条件相比,变温条件不能起到促进紫花针茅种子萌发的作用;不同居群紫花针茅种子萌发对温度的响应既有相同点,也有不同点;海拔高度与种子萌发率存在极显著负相关关系,种子萌发季土壤温度与种子萌发存在显著负相关关系。本研究将为合理的保护和恢复紫花针茅草地提供一定科学依据。     

温度变化对油菜及其伴生杂草种苗生长和幼苗生理特性的影响

以目前大面积栽培的甘蓝型油菜(Brassica napus) ‘秦优10号’和其田间常见的8种杂草播娘蒿(Descurainia sophia)、泽漆(Euphorbia helioscopia)、野燕麦(Avena fatua)、棒头草(Polypogon fugax)、婆婆纳(Veronica didyma)、看麦娘(Alopecurus aequalis)、灰绿藜(Chenopodium glaucum)、反枝苋(Amaranthus retroflexus)为试验材料, 利用人工气候培养箱控温, 研究了10 ℃/5 ℃ (昼/夜)、18 ℃/10 ℃、25 ℃/20 ℃、35 ℃/30 ℃、40 ℃/35 ℃不同温度幅度处理对它们的发芽势、发芽率、幼苗形态及生理指标的影响, 旨在为预测气候变化环境下油菜田恶性靶标杂草的演替趋势提供参考依据。试验结果表明: 不同供试杂草对温度变化表现出明显的适应性差异, 看麦娘、灰绿藜和反枝苋的最适萌发温度偏高, 如反枝苋在高温处理(40 ℃/35 ℃)下种子的发芽率达到最高(91%); 而播娘蒿、泽漆、野燕麦、棒头草、婆婆纳种子的最适萌发温度主要集中于10-18 ℃范围内。进一步测试研究表明, 高温处理(40 ℃/35 ℃)下, 反枝苋幼苗生长旺盛, 体内丙二醛的积累也明显低于低温(10 ℃/5 ℃)处理, 可溶性糖和可溶性蛋白含量以及保护酶活性也较高, 表明反枝苋对高温胁迫有较好的适应性, 灰绿藜对高温的响应与反枝苋相似, 在高温气候年份, 要严防这2种草害加重; 而在低温处理(10 ℃/5 ℃)下, 野燕麦的种子萌发率达到100%, 其幼苗生长旺盛, 体内可溶性糖和可溶性蛋白含量及保护酶活性较高, 播娘蒿对低温胁迫的响应类似于野燕麦, 因此在寒冷年份需加强对野燕麦和播娘蒿草害的预防。供试油菜品种相对于所有供试杂草对温度变化的适应性更好, 其种子在不同温度处理下均保持较稳定的高发芽率, 且幼苗长势良好, 表明‘秦优10号’是一个对温度变化适应性很好的油菜品种。     

Effects of biological soil crusts on a Mediterranean perennial grass (Stipa tenacissima L.)

In the last decades, there has been a growing interest on evaluating the effects of biological soil crusts (hereafter, biocrusts) on vascular plants. The purpose of this paper was to investigate the influence of biocrusts on Stipa tenacissima, key species in arid and semi-arid environments of the Mediterranean Basin. In fact, we explored the impact of biocrusts removal underneath S. tenacissima on soil chemical properties and leaf mineral uptake. Indeed, we studied the effect of mixed biocrusts on the seed germination of S. tenacissima under laboratory conditions. The research showed a greater availability of soil resources correlated with enhanced leaf nutrient levels of bioessential elements in the presence of intact biocrusts compared to fragmented biocrusts underneath S. tenacissima tussocks. We suggest that this is related to the loss of soil moisture as a result of biocrusts removal. In addition, we found that mixed biocrusts favored seed germination and viability of S. tenacissima. By improving soil chemical properties and leaf nutrient uptake, biocrusts can provide enhanced growth conditions for Stipa tenacissima. These findings with the positive effect on seed germination suggest that biocrusts can be used in the restoration of S. tenacissima.     

Requirement of vegetation gaps for seedling establishment of two unpalatable grasses in a native grassland of central Argentina

Abstract The objective was to determine the effects of root and shoot competition on seedling establishment of the unpalatable grasses Stipa gynerioides and S. tenuissima in a native grassland of central Argentina dominated by the palatable grass S. clarazii. Seeds of the two unpalatable species were sown in natural occurring microsites with shoot and root competition from the palatable species, and in artificially created microsites without either shoot competition or shoot and root competition. In addition, fresh seeds of the unpalatable species were subjected to daily alternating temperatures under laboratory and field conditions to determine the effect on seed dormancy and germination. Seedling establishment of S. gynerioides and S. tenuissima occurred only in microsites without shoot and root competition. Also, the fluctuation of temperature near the soil surface in these microsites reduced dormancy and promoted rapid germination in both species. Our results support the hypothesis that, in swards dominated by palatable grasses, vegetation gaps of low competitive pressure favour seedling establishment of unpalatable grasses. It is suggested that the creation of these gaps by overgrazing can be an important mechanism in the process of species replacement in native grasslands.     

Seed dormancy and longevity in <Emphasis Type="Italic">Stipa tenacissima</Emphasis> L. (Poaceae)

In the present paper we studied the life history traits related to seed germination of Stipa tenacissima, a key species in semiarid environments of western Mediterranean areas. S. tenacissima is a perennial tussock grass, which has traditionally been considered to expand mainly by vegetative propagation with little or no sexual reproduction. We analysed seed longevity as well as the type of seed dormancy and the role of the seed covers from seeds collected from different populations in SE Spain. We also studied the variation in seed germinability among populations, individuals, and years and the ability of seeds of S. tenacissima to form soil seed banks. There was significant variation in seed germination among individuals, populations and years. Lemma and palea were the main factor controlling these differences since their removal promoted higher and faster germination and eliminated the differences in germination parameters among populations. However, the control of dormancy by lemma and palea was independent of their weight, suggesting that their chemical nature plays a more important role than does size in controlling seed germination. Mechanical scarification treatments (via abrasion with sand) did not affect seed germination. The decay in seed germinability two years after seed collection and the low density of viable seeds in soils one year after seed dispersal indicated that S. tenacissima forms transient soil seed banks.     

Germination responses of Reaumuria vermiculata to salinity and temperature

Reaumuria vermiculata is a xerohalophytic perennial dwarf shrub distributed in many gypseous and saline areas in southern Tunisia. A laboratory experiment was carried out to assess the effects of temperature and salinity on germination. The germination responses of the seeds in darkness were determined under a range of salinity and temperature regimes. Temperatures between 10°C and 30°C seem to be favourable for the germination of this species. Germination was inhibited by either an increase or a decrease in temperature from the optimal temperature (15°C). Highest germination percentages were obtained under non-saline conditions and increases in salinity inhibited seed germination. Salt stress decreased both the germination percentage and the germination speed (increase of the mean time to germinate). Seed germination decreased with an increase in NaCl concentrations at all temperatures. An interaction between salinity and temperature yielded no germination at salinity of 300 mM, whereas some seeds germinated under the optimal temperature.     

Light, salinity, and temperature effects on the seed germination of perennial grasses

The germination requirements of four perennial halophytic grasses, Aeluropus lagopoides, Halopyrum mucronatum, Sporobolus ioclados, and Urochondra setulosa, were studied under control conditions in the laboratory. Treatments included two light levels (12?:?12 h light?:?dark period and 24-h dark environment), six salinity concentrations (0, 100, 200, 300, 400, and 500 mmol/L NaCl), and four temperature regimes (fluctuating day?:?night temperature regimes of 10°?:?20°, 15°?:?25°, 20°?:?30° and 25°?:?35°C), using a completely randomized block design. Best seed germination of all grasses was obtained in a distilled water control. Increase in salinity progressively inhibited germination of all species. For example, few seeds of H. mucronatum germinated above 300 mmol/L NaCl, while seeds of the other grasses germinated in up to 500 mmol/L NaCl. Optimal temperature regime for germination for all species was 20°?:?30°C both for light- and dark-germinated seeds. At higher temperatures differences between light and dark treatments were not significant. Absence of light had no effect on the seed germination of U. setulosa and H. mucronatum; however, germination was lower in all salinity treatments. In the case of A. lagopoides, absence of light substantially inhibited the germination both in control and saline conditions. The light effect was marked in the case of S. ioclados, which showed very low germination in the absence of light both under saline and nonsaline conditions.     

Germination ecology of Central Asian Stipa spp: differences among species, seed provenances, and the importance of field studies

Stipa-species are wide-spread in Central Asia, but sexual reproduction in the dry steppes is rare. To facilitate conservation and restoration of these important rangelands, we studied germination characteristics of three common Mongolian Stipa-species under field- and lab conditions. Seeds of Stipa krylovii, Stipa gobica and Stipa glareosa were sown at the study site in Southern Mongolia over two consecutive years during which period tests were carried out to ascertain whether competition or herbivory are the main constraints of seedling establishment. In addition, we tested germination and seed viability in the laboratory under two different temperature regimes (20/10°C and 8/4°C), as well as the effect of cold-stratification. The lab experiments also included S. krylovii seeds originating from three climatically different provenances. None of the three Stipa-species seedlings emerged during the first 2 years of the field study. However, after an unusually intense rain event in the third year, 3% of S. krylovii, 0.6% of S. glareosa and 0.1% of S. gobica seeds germinated in the study plots. The factors ‘sowing-year’ and ‘vegetation’ significantly affected seedling emergence, whereas grazing had no effect at all. Under laboratory conditions a high percentage of viable seeds of S. gobica and S. glareosa germinated at both incubation temperatures, and cold-stratification had no effect on germination or viability. Germination of S. krylovii seeds required warmer temperatures and cold-stratification had a positive effect. Such evidence for dormancy was more pronounced in seeds from the moister, northern provenances. Germination of Stipa-species in the field is rare and only possible under exceptionally moist conditions. Conservation should thus concentrate on steppe conservation rather than on restoration. Where artificial reseeding is necessary, differences among species and also among different seed provenances should be taken into account.     

松嫩平原退化草地羊草种子萌发对环境因子的响应

研究了温度(恒温和变温)、水分(含水量2.5%-40.0%)和干旱胁迫、土壤类型(盐碱土和非盐碱土)和盐碱胁迫(NaCl和Na₂CO₃)等环境因子对羊草(Leymus chinensis)种子萌发的影响。恒温下未经打破休眠处理的羊草种子发芽率不足2%, 变温下羊草种子发芽率可达85.3%, 表明温度是影响羊草种子萌发的关键因素之一。羊草种子萌发的适宜土壤含水量为2.5%-15.0%, 随着含水量继续增加, 发芽率呈下降趋势。松嫩平原盐碱化土壤对羊草种子萌发具有显著的抑制作用, 羊草种子在重度盐碱土(pH 10.24)中发芽率仅为6.0%, 而在非盐碱土中发芽率可达61.3%。羊草种子在萌发阶段的耐盐碱能力差, 随着NaCl和Na₂CO₃浓度增加, 发芽率呈显著下降趋势, 且Na₂CO₃的抑制作用更强。松嫩平原盐碱环境下羊草种子萌发受到抑制是该地区羊草草地退化的原因之一。     

Seed germination responses to salinity and temperature in Limonium supinum (Plumbaginaceae), an endemic halophyte from Iberian Peninsula

Limonium supinum, a perennial herb with interest for the restoration and gardening of arid zones, is widely distributed in saline areas from southeastern Iberian Peninsula. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and on germination recovery from the effects of saline conditions after transfer to distilled water. Seed germination responses were determined over a four temperature regimes (20/10, 25/15, 30/20 and 35/25 °C; 12 h light/12 h dark photoperiod) and six salinities (0, 100, 150, 200, 400 and 600 mM NaCl). The higher germination percentages were obtained in non-saline conditions, under all temperature regimes. An alternating temperature of 20 °C light and 10 °C dark yielded the maximum germination for any saline concentration. Increase in salinity delayed the beginning and end of germination and reduced the final percentage of germination, which becomes completely inhibited at 600 mM NaCl. The adverse effect of salinity is reinforced by high temperatures (30/20 and 35/25 °C). The germination rate was also negatively affected by the increase in salinity and temperature. The final recovery percentages in high salt treatments were near 100%, indicating that exposure to high concentration of NaCl did not inhibit germination permanently.     

Seed weight and germination behavior of the submerged plant Potamogeton pectinatus in the arid zone of northwest China

Variation in seed weight is common within and among plant species, but few studies have attempted to document the pattern of seed weight and germination attributes for aquatic macrophytes at a large scale. This study examined within‐species variation in seed weight and germination attributes and the effects of environmental factors on seed traits of the submerged plant Potamogeton pectinatus in the arid zone of northwest China. Our results showed that the average seed weight was 0.24 g per 100 seeds with a coefficient of variation (CV) of 28.4% among the eight P. pectinatus populations. The total germination fraction of seeds of P. pectinatus was relatively poor, less than 35% in seven P. pectinatus populations, and the lowest germination percentage found was only 2%. There were significant differences in seed weight, time to onset of germination, and total germination fraction among the eight different populations. Hierarchical partitioning analysis showed a strongly positive correlation between seed weight and water temperature and pH. Seed weight and the maternal environmental factors significantly affected both time to initiation of germination and total germination fraction. Our results suggest that (1) seed weight variation in P. pectinatus primarily is the result of temperature variation during fruit development; (2) relatively poor germination fraction suggests that seeds are relatively unimportant in the short‐term survival of populations and that it may be another adaptive trait allowing plants to take place in the right place and at the right time, especially in harsh environment; and (3) variation in seed germination traits should be determined by local environmental and intrinsic factors that interact in a complex fashion.     

Variation in temperature and light but not salinity invokes antioxidant enzyme activities in germinating seeds of Salsola drummondii

Seeds with efficient antioxidant defence system show higher germination under stress conditions; however, such information is limited for the halophyte seeds. We therefore studied lipid peroxidation and antioxidant responses of a leaf-succulent halophyte Salsola drummondii during seed germination under different salinity levels (0, 200 and 800 mM NaCl), temperature (10/20, 20/30 and 25/35°C) and light regimes. Seeds absorbed water and germinated in less than 1 h in non-saline control while increases in salinity decreased the rate of water uptake as well as seed germination. Non-optimal temperatures (10/20 and 25/35°C) and complete dark condition reduced seed germination in comparison to those seeds germinated under optimal temperature (20/30°C) and 12-h photoperiod, respectively. Generally, higher lipid peroxidation and antioxidant enzyme activities were observed in seeds at non-optimal temperature and in those seeds germinated in dark. Decrease in reduced ascorbic acid content was found in highest salinity and temperature treatments, while reduced glutathione content did not change significantly with changes in salinity, temperature and light regimes. These results indicate variation in temperature and light but not salinity enhances antioxidant enzyme activities in germinating seeds of Salsola drummondii.     

Cold tolerance in tomato. I. Seed germination and early seedling growth of Lycopersicon esculentum

Tomato seed germination times were evaluated foi three "cold germinating" Lycopersicon esculentum Mill, accessions, PI 120256, PI 174263 and PI 341988 and a control breeding line, T3, at temperatures of 6 to 20°C. Accelerated failure analysis indicated that although PI 120256, 174263 and 341988 germinated more rapidly than T3 from 20 to 9°C, the minimum temperatures for germination were similar, and germination times of PI 120256 and 341988 were relatively more inhibited by progressively lower temperatures than was T3. Rapid germination of these three Pls at 10°C may not be due to cold tolerance, but to seed characteristics that promote rapid germination. Hypocotyl and root elongation over time were described by a three-parameter logistic equation; the growth rate parameter for hypocotyl elongation of all four genotypes was greatly inhibited from 20 to 15 and 10°C. Multivariate and univariate analyses of hypocotyl growth parameters indicated significant differences among accessions, but no significant genotype by temperature interaction. Rapid emergence reported for these Pis at 10°C is attributable to early germination, rather than rapid hypocotyl growth.     

感染内生真菌的羊草对克氏针茅种子萌发的影响

以我国内蒙古草原常见优势种羊草（Leymus chinensis（Trin.) Tzvel.）及克氏针茅（Stipa krylovii Roshev.）为实验材料,在离体器官和整株植物水平上探讨内生真菌感染是否会影响宿主植物羊草对克氏针茅种子萌发的作用。实验结果表明：内生真菌感染能够影响羊草对克氏针茅种子萌发的作用,其影响程度与羊草的作用部位、处理方法以及处理浓度相关。与未染菌羊草相比,染菌羊草绿叶在低浓度处理下显著促进了克氏针茅的萌发,高浓度下显著抑制了克氏针茅的幼根生长;染菌羊草枯叶显著抑制了克氏针茅幼根的生长,而染菌羊草地下部显著促进了克氏针茅的萌发;感染和不感染内生真菌的整株羊草对克氏针茅的发芽率和发芽速度无显著影响。在处理浓度相同的情况下,草粉对克氏针茅种子萌发的抑制作用比浸提液处理更为显著,绿叶比枯叶抑制作用更为显著。     

不同居群准噶尔无叶豆果实和种子特性及种子萌发差异

研究准噶尔无叶豆(Eremosparton songoricum) 6个居群间果实和种子特性及种子萌发差异, 以揭示异质生境下准噶尔无叶豆果实和种子的生态适应机制。结果显示: 居群间准噶尔无叶豆的植株距离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49, p < 0.01)存在显著差异, 沙漠北缘E、F居群和沙漠腹地C居群(受人类干扰剧烈)的植株距离和植株冠幅高于沙漠腹地A、B、D居群; 居群间准噶尔无叶豆果实和种子的长度、宽度、厚度、重量存在显著差异, 居群E、F和C的大部分参数显著高于其他沙漠腹地居群; 居群间果实多子性(F = 6.96, p < 0.01)也存在显著差异, 居群C的果实多子性最高((32.50 ± 4.79)%); 萌发结果表明, 居群间新鲜的成熟种子萌发不存在显著差异, 且萌发率都低于15%; 所有居群的大部分种子都存在物理性休眠现象, 人为划破种皮能显著提高种子萌发率, 但在低温(15/5 ℃)条件下, 所有居群的种子萌发率都较低, 说明低温抑制了种子萌发; 经人为划破种皮解除物理休眠后, 种子的休眠没有完全释放, 居群C、E和F (大种子居群)的种子萌发率显著高于居群A、B和D (小种子居群) (F = 30.77, p < 0.01), 说明准噶尔无叶豆种子不仅存在物理性休眠现象, 也可能存在生理休眠现象。不同程度的种子复合休眠可能是准噶尔无叶豆不同居群适应古尔班通古特沙漠的重要生存策略。     

Germination responses of a non-dormant seed population of Amaranthus patulus Bertol. to constant temperatures in the sub-optimal range

Abstract. The germination responses of a nondormant seed population of Amaranthus patulus Bertol, at constant sub-optimal temperatures in the range of 10–34°C were analysed through a detailed time-course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage, v. temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required 'thermal times' (θ), the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution and A is a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol⁻¹ with all 20–80% subpopulations.     

Geographic variation in the flood-induced fluctuating temperature requirement for germination in Setaria parviflora seeds

Our aim was to search for specific seed germinative strategies related to flooding escape in Setaria parviflora, a common species across the Americas. For this purpose, we investigated induction after floods, in relation to fluctuating temperature requirements for germination in seeds from mountain, floodplain and successional grasslands. A laboratory experiment was conducted in which seeds were imbibed or immersed in water at 5°C. Seeds were also buried in flood-prone and upland grasslands and exhumed during the flooding season. Additionally, seeds were buried in flooded or drained grassland mesocosms. Germination of exhumed seeds was assayed at 25°C or at 20°C/30°C in the dark or in the presence of red light pulses. After submergence or soil flooding, a high fraction (>32%) of seeds from the floodplain required fluctuating temperatures to germinate. In contrast, seeds from the mountains showed maximum differences in germination between fluctuating and constant temperature treatment only after imbibition (35%) or in non-flooded soil conditions (40%). The fluctuating temperature requirement was not clearly related to the foregoing conditions in the successional grassland seeds. Maximum germination could also be attained with red light pulses to seeds from mountain and successional grasslands. Results show that the fluctuating temperature requirement might help floodplain seeds to germinate after floods, indicating a unique feature of the dormancy of S. parviflora seeds from floodplains, which suggests an adaptive advantage aimed at postponing emergence during inundation periods. In contrast, the fluctuating temperature required for germination among seeds from mountain and successional grasslands show its importance for gap detection.     

Germination Responses of Taraxacum platycarpum Seeds to Temperature

Abstract Germination responses of Taraxacum platycarpum seeds to temperature were examined under laboratory conditions to investigate the emergence-season choice mechanism of the seeds. Almost all the newly collected seeds were non-dormant. Under constant temperature conditions, maximum percentage germination (approximately 90%) was attained at temperatures 6–16°C, where simple linear relationships were observed between the temperature and the rates of germination, i.e. the reciprocals of the time taken to germinate by seed subpopulations with 10–80% germination. Thermal time required for germination of the subpopulations ranged from 600 Kh (degree Kelvin × hours) to 1500 Kh with a relatively constant base temperature of about 2.5°C. Lower limit temperature for germination was slightly below 6°C. Higher limit temperature for germination has the normal distribution with the mean ±SD of 19±2.5°C. Pre-exposure of imbibed seeds to temperatures higher than the higher limit temperature for germination, 25 and 30°C, had no effect on the germinability and the rate of germination at a circa-optimum temperature. Moist chilling treatment at 4°C caused an increase in the variation of germination rate within the seed population, but no evidence for dormancy-inducing or breaking effects was obtained.     

Germination behaviour of Conyza bonariensis to constant and alternating temperatures across different populations

Conyza bonariensis is one of the most problematic weed species throughout the world. It is considered highly noxious due to its interference with human activities, and especially the competition it poses with economically important crops. This research investigated the temperature requirements for seed germination of four populations of C. bonariensis with distinct origin and the influence of daily alternating temperatures. For this, a set of germination tests were performed in growth chambers to explore the effect of constant and alternating temperatures. Seeds of the four populations (from Lleida, Badajoz and Seville, Spain and Bahía Blanca, Argentina) were maintained at constant temperatures ranging from 5 to 35°C. The final germination and cardinal temperatures (base, optimum and maximum) of each population were obtained. We also tested the influence of daily alternating temperatures on final germination. To do so, seeds were exposed to two temperature regimes: 5/15, 10/20, 15/25, 20/30 and 25/35°C night/day temperature (intervals increasing 5°C, with constant oscillation of 10°C) and to 18/22, 16/24, 14/26, 12/28 and 10/30°C night/day temperature (intervals with average of 20°C, but increasing the oscillation in 4°C between intervals). In general, all populations behaved similarly, with the highest germination percentages occurring in the optimum temperature range (between 21.7°C and 22.3°C) for both constant and alternating temperatures. In general, climatic origin affected germination response, where seeds obtained from the coldest origin exhibited the highest germination percentage at the lowest temperature assayed. In addition, we observed that the alternating temperatures can positively affect total germination, especially in oscillations that were further from the average optimum temperature (20°C), with high germination percentage for the oscillations of 15/25, 20/30, 18/22, 16/24, 14/26, 12/28 and 10/30°C in all populations. The cardinal temperatures obtained were significantly different across the populations. These results provide information that will facilitate a better understanding of the behaviour of Conyza and improve current field emergence models.     

Effect of Temperature Regimes on Germination of Dimorphic Seeds of Atriplex prostrata

Dimorphic seeds of Atriplex prostrata were removed from cold dry storage monthly over a one year period to test for fluctuations in seed dormancy and germination rate. For each seed type, four replicates of 25 seeds were exposed to four alternating night/day temperature regimes mimicking seasonal fluctuations in Ohio: 5/15 °C; 5/25 °C; 15/25 °C and 20/35 °C with a corresponding 12-h photoperiod (20 μmol m⁻² s⁻¹; 400 – 700 nm). We found a significant three-way interaction of seed size, temperature and month for both percent germination and the rate of germination. Large seeds showed the greatest germination at the 20/35 °C and 5/25 °C temperature regimes and small seeds at the 5/25 °C regime. Large seeds had greater germination at all temperatures as compared to small seeds. Large seeds had the fastest germination rates at 20/35 °C followed by 5/25 °C whereas small seeds had the fastest rates at 5/25 °C followed by 20/35 °C. This revised version was published online in July 2006 with corrections to the Cover Date.