Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence

Trials were carried out to investigate the effects of light and temperature on germination of Rumex obtusifolius L. After several months of storage, seeds gradually lost dormancy and became photosensitive. Thermal optima for germination were between 20 °C and 25 °C in light or in darkness. At lower temperatures there was a greater demand for light, so that the greatest differences in germination percentage (between low and high temperatures) were found within the 10–15 °C temperature range. The calculated thermal minima ( x -intercept method) in light and darkness were 8.3 °C and 6.1 °C respectively. Daily temperature fluctuation increased germination even after seed irradiation with far-red light, suggesting a lower demand for the far-red-absorbing form of phytochrome. Seed burial inhibited germination in proportion to depth; however, germination inhibition was independent of seed phytochrome photo-equilibrium, which had been diversified by seed pretreatment with light. Seedlings did not emerge when seeds were buried >8 cm deep. Recovery of ungerminated seeds showed that excessive burial did not impede seedling emergence but rather prevented seed germination. However, this induction of dormancy was lost once germination processes were activated (24–48 h at 20 °C) that made germination irreversible. Temperature was also involved in inhibition, and low temperature (<15 °C) induced the least inhibition. This is discussed in terms of processes of respiration and fermentation in buried seeds.     

A viability study of Fallopia japonica stem tissue

Vegetative regeneration of intact and split nodes of Fallopia japonica (Houtt.) Ronse Decraene was the focus of this greenhouse experiment. Stem material, collected in May, July and September 1997, was cut into 40-mm-long sections and incubated on the surface of moist compost in a greenhouse. All samples showed some regrowth of buds and new shoots from both intact and split nodes in any season. A maximum number of 0.25 buds per intact node was recorded after 6 days in a spring experiment. The vegetative regrowth of shoots generally appeared after 1 week and increased over time with a maximum mean height of 77 mm after 27 days and a maximum number of 0.39 shoots per intact node after 13 days. Adventitious roots developed from both intact and split nodes during both summer and autumn experiments. From this study, a maximum of 90 stem tissue propagules per square metre of F. japonica stand has been estimated. If the plant is cut as part of a control programme, these propagules can produce shoots with growth rates of up to 2.9 mm per day with a good chance of the development of adventitious roots. This considerable potential for vegetative regeneration of stem tissue shows a clear need for guidelines on the safe management and disposal of F. japonica plant material.     

Potential of weed seedbanks for managing weeds: a review of recent New Zealand research

Weed seedbanks are the primary source of weeds in cultivated soils. Some knowledge of the weed seedbank may therefore be appropriate for integrated weed management programs. It would also be very useful in planning herbicide programs and reducing the total herbicide use. However, a number of problems are inherent in the estimation of the seedbank size for arable weeds that usually have annual life cycles. In a long-term research project we have investigated the dynamics of weed seedbanks in corn fields for the past 8 years. Specific studies have included (i) developing cheap and efficient methods for estimating the weed seedbank; (ii) developing guidelines for efficient soil sampling (including the number and size of samples); (iii) influence of cultivation methods on weed seed distribution; (iv) mapping the spatial variability of the seedbank; (v) estimating the rate of seedbank decline for certain weed species; and (vi) assessing the potential of using the weed seed content in the soil to predict future weed problems. This paper reviews and summarizes the results of our research on the above aspects. The strong correlation between seedlings emerged in the greenhouse and seeds extracted in the laboratory for the most abundant weed species has demonstrated the potential for using the weed seed content of the soil to predict future weed infestations. The next step is to establish correlations with field emergence under commercial conditions using the sampling guidelines developed in our studies. Subsequently, we aim to offer the weed seedbank estimation as a commercial service to farmers for planning the most appropriate weed management options.     

Cohort-dependent seedling recruitment, survival and reproductive capacity of Tribulus terrestris

Knowledge of the population biology of the summer annual Tribulus terrestris can provide valuable information for managing the risk of its colonising crop fields. Because of spring‐summer crop management practices, fields can exhibit bare ground in late April and early May. In this situation, four cohorts in 2000 and three cohorts in 2001 were censused and monitored throughout the vegetative and reproductive season, in order to evaluate the relationship between time of emergence, survival, vegetative growth and plant reproductive capacities. To a great extent, seedling survivorship depended on emergence timing; the earlier the emergence of the seedlings, the higher was the proportion of survivorship (64% and 4%, for early and late emergences). The time of emergence also influenced plant development; in both years, surviving individuals of the first cohorts presented significantly greater plant biomass and larger numbers of reproductive structures (60.5 fruits per plant) than those of later cohorts (0.8 fruits per plant). Reproductive meristem allocation was also highest in the earliest cohorts. Results showed that T. terrestris can increase its population size in fields if gaps of bare soil surface are available from mid spring to early summer.     

Salinity and Temperature Effects on Seed Germination of Milk Thistle

Abstract

Milk thistle [Silybum marianum (L.) Gaertn] is an annual plant belonging to the Asteraceae family whose ripe seeds contain flavonoid substances, which are important in the modern pharmaceutical industry. Seed germination is a major factor limiting the establishment of plants under saline conditions. The effect of salinity and temperatures on germination and seedling establishment was studied in two genotypes of milk thistle, an Iranian wild type and German (Royston) type in the laboratory and in the field. Experiments were done with seven salt concentrations [0.1 (control), 1, 3, 6, 9, 12, and 15 dS/m] and three temperatures (15, 25, and 35°C). There were three replications for each treatment, and the experiment was run three times. The results showed that the percentage of germination and the number of normal seedlings at different salt treatment at 15°C were higher than at 25 or 35°C. The mean time to 50% germination was least at this temperature for both genotypes. Results suggested all germination indices and seedling emergence (50%) were achieved at levels up to 9 dS/m salinity at 15°C. Also, seeds at a salinity of 9–15 dS/m will germinate and up to 25% of the control nonstress treatment could emerge at the low temperature of 15°C.     

混交林纯林中毛竹出笋退笋特性研究

应用出笋量的逻辑斯谛 ( L ogistic)模型研究了出笋量随时间增长的变化规律 ,结果表明 :出笋前期 (前 1 0 d)出笋数占总数的 1 5%左右 ,出笋中期 (第 1 0～ 2 0天 )占 75%,出笋末期 (第2 0天以后 )占 1 0 %;对退笋特征的观察及其规律的研究得出 :出笋前后期退笋数量少但退笋率高 ,而出笋中期退笋数量多但退笋率低 .小于 1 0 cm的浅鞭竹笋多属退化笋 .纯林中的出笋比混交林中的出笋持续天数短 ,退笋率高 ,为此混交林更有利于竹笋的生长 .出笋退笋规律可用来指导生产 ,为留养和挖取竹笋数量提供依据     

义乌游泳馆屋盖风荷载的试验研究

义乌游泳馆采用凹形屋盖,对这种屋盖结构的风荷载研究还比较少.为此,制作了比例为1:100的刚性模型,采用同步测压技术,进行了义乌游泳馆凹形屋盖的风压测量,得到了其屋盖上的平均风压系数分布并与凸形屋盖的试验结果进行比较.结果表明:凹形屋盖上的“吸力”要远大于凸形屋盖上的“吸力”;迎风向挑棚上、下表面压力出现不利的负相关,应引起设计人员的注意;周边建筑对义乌游泳馆屋盖风荷载的影响不大.最后还给出了义乌游泳馆屋盖上的前10个最小极值风压.     

Influence of physiological ageing of seed potatoes on yield and earliness

Summary Ageing seed potatoes at ambient temperatures after long storage (26 weeks) at 2 °C affected rate of plant emergence and yields of three potato cultivars in Cyprus. Sprout growth at ambient increased until planting, and was bigger in cv. Spunta than in cv. Arran Banner and cv. Cara. Four weeks after planting the rate of emergence was higher in physiologically younger seed; total emergence was not affected but average yields were reduced by ageing. Early yields were less affected but final yields were significantly reduced by ageing; these effects were moro pronounced in Spunta and Arran Banner, early and medium maturity cultivars respectively than in Cara, a late maturity cultivar. Ageing of seed at ambient temperature was rapid and removing seed to ambient for more than 3 weeks before planting to save storage costs adversely affected final yields.

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Zusammenfassung Eine nach verl?ngerter Lagerung bei 2 °C erfolgte Alterung der Saatkartoffeln bis zu 9 Wochen in der Umgebungstemperatur beeinflusste bei den Sorten Arran Banner, Spunta und Cara das Auflaufen der Pflanzen und die Ertr?ge. Das Keimwachstum wurde nach überführung aus dem Kaltlager in die Umgebungstemperatur bis zum Auspflanzen nicht unterbrochen; die Keime von Spunta waren l?nger als diejenigen von Arran Banner und Cara (Abb. 1). Bei physiologisch ?lterem Saatgut liefen die Pflanzen schneller auf als bei jüngerem (Tab. 1). Fünf Wochen nach dem Auspflanzen war die Auflaufrate in allen Behandlungen ?hnlich und gr?sser als 80 % (Tab. 1). Drei Wochen nach dem Auspflanzen war die Auflaufrate der Pflanzen durch die Alterung erh?ht. Die Zwischen- und Endertr?ge wurden durch die Alterung signifikant beeinflusst Saatgut, das l?nger als 3 Wochen in der Umgebungstemperatur gehalten wurde, erbrachte geringere Zwischen- und Endertr?ge. Die Frühertr?ge wurden durch die Alterungsbehandlungen weniger beeinflusst (Tabellen 2, 3 und 4). Die Saatkartoffeln alterten schneller nach überführung in die Umgebungstemperatur und ein Verbleiben des Saatgutes in der Umgebungstemperatur für mehr als 3 Wochen führt zu geringeren Ertr?gen. Wenn auch der Alterungsprozess w?hrend der Kaltlagerung fortschreitet, ist eine Verl?ngerung der Kaltlagerzeit wünschenswert, um dann das Saatgut in die Umgebungstemperatur zu übertragen und dadurch Lagerkosten zu sparen.

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Résumé Le vieillissement physiologique de plants de pomme de terre obtenu par la conservation à la température ambiante pendant des durées de 0 à 9 semaines après un maintien prolongé à 2 °C, affecte la levée et le rendement des variétés Arran Banner, Spunta et Cara. Après que les tubercules aient été sortis de chambre froide, la croissance des germes se poursuit jusqu'à la plantation. Les germes de Spunta sont plus longs que ceux d'Arran Banner et de Cara (fig. 1). La levée des plants est plus rapide chez ceux physiologiquement vieux que chez ceux physiologiquement jeunes (tableau 1). Cinq semaines après la plantation, le taux de levée est identique dans tous les traitements et dépasse 80% (tableau 1). La levée des plants trois semaines après la plantation est accrue par le vieillissement. Les rendements intermédiaires et finaux sont significativement affectés par le vieillissement. Les plants placés pendant plus de 3 semaines à température ambiante donnent de plus faibles rendements intermédiaires et finaux. La précocité des rendements est moins affectée par les traitements de vieillissement (tableaux 2, 3 et 4). Les plants vieillissent plus rapidement à la température ambiante et ceux conservés plus de trois semaines dans ces conditions donnent une réduction de rendement. Toutefois, le processus de vieillissement se poursuit également durant la période de conservation au froid aussi l'extension de la durée de cette période est préférable à cette de la mise à température ambiante lorsqu'elle est réalisée dans un but d'économie.

     

Which model species for weed seedbank and emergence studies? A review

Models predicting the effects of cropping systems on weed demography are important tools for testing new rules for integrated weed management that may reduce the use of herbicides and preserve the biodiversity of agro-ecosystems. Such models already exist for a few species and should now be extended to a larger flora, in order to predict and understand the effects of agricultural practices on the evolution of weed communities. This review analysed the literature from 1973 to 2006, focusing on 45 species, to identify past reasons for choosing particular species when modelling the effects of cropping systems on the processes leading to seedling emergence. The frequency or harmfulness of the species were the main reason for studying them. It appears that the studied species were mainly autumn-emerging in north-western Europe cropping systems and summer-emerging in North America; the effects of deep soil tillage were studied mainly in Europe, as simplified sowing techniques are more often practised in North America. A voluminous literature exists on seed persistence in the soil, dormancy, germination and emergence, but rarely with the attempt of establishing generic relationships between species characteristics and model parameters. Until now, such an approach has been mostly developed in ecological studies. Taxa, as well as ecological preferences, seed size and the relationships of these characteristics with weed emergence model parameters should be considered when selecting a range of species for multi-specific modelling purposes.     

福建省重大林业有害生物灾害及应急管理对策

划分了福建省重大林业有害生物灾害类型,总结了重大林业有害生物灾害发生特点,并针对灾害发生形势和防控存在问题,阐述了应急管理的必要性,综合提出应急管理的对策。