The levels of GA3 and GA20 may be associated with dormancy release in Onopordum nervosum seeds

Endogenous levels of two gibberellins, GA₃ andGA₂₀, were quantified in unimbibed Onopordumnervosum seeds collected from two different populations, whichshoweddifferences in their germination capacity. After purifying the seed extracts,gibberellin levels were evaluated by gas chromatography mass spectrometry byusing selected ion monitoring (GC-MS-SIM) adding deuterated gibberellins asinternal standards. The intraspecific differences in germination capacity wereassociated with differences in the endogenous levels of both gibberellins. Thecontents of GA₃ and GA₂₀ in seeds with high germinationrate were twice and five times higher, respectively, than those from seeds witha low germination rate, indicating a possible role of gibberellins in dormancyrelease in this plant species.     

Effects of long‐term cutting in a grassland system: perspectives for restoration of plant communities on nutrient‐poor soils

Abstract. The upper courses of brook valley systems harbour Nardo‐Galion saxatilis communities characteristic of oligo‐trophic soils under low‐intensity farming. Most of these communities have disappeared under intensified farming i.e. application of fertilizers. We studied the possibilities of restoration i.e. re‐establishment of the former plant community by adopting various cutting regimes after the cessation of fertilization in 1972. The various cutting regimes revealed different effects after 25 yr. Regimes with cutting every second year with or without removal of the swath, and complete abandonment deviated from the other regimes that included annual haymaking with different frequency and timing. The latter group of cutting regimes came closer to the community of an adjacent field where fertilization stopped in 1967. This field in turn harboured several Nardo‐Galion species after 25 yr of annual cutting, and showed more resemblance with a local reference community (at a distance of 500 m) that had not been fertilized since the 1940s. The local reference still does not match poorly developed Nardo‐Galion saxatilis communities found in the region of ca. 50 km around the study area, and is far from well developed Nardo‐Galion communities in the same region. The study site still harbours several species characteristic of eutrophic soil and few species characteristic of oligotrophic soil after 25 yr of annual cutting and removal of the swath. The soil seed bank harbours only few target species. Although species characteristic of oligotrophic soil are present in an adjacent field and Nardo‐Galion saxatilis species occur at 500 m, they have not (yet) established in the target area.     

Seed dormancy in relation to seed storage behaviour in Acer

Dormancy in seeds of Acer opalus is shown to be mainly caused by the seed coats, although a slight embryo dormancy exists in fresh seeds. The ability to germinate after drying indicates that seed storage behaviour is orthodox. Recalcitrant seeds were heavier than orthodox seeds not only within section Acer but also within the whole genus after statistical control of phylogeny, through a phylogenetic ANOVA with data from two different Acer phylogenies. An evolutionary change from orthodox to recalcitrant behaviour is postulated for genus Acer , but this change appears not to have been accompanied by a change in seed dormancy, at least in the taxonomic section in which Acer opalus belongs.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 203–208.     

Immediate increase in plant species richness after clear‐cutting of boreal herb‐rich forests

Abstract. The flora of clear‐cuttings with soil scarification in forests was compared < 1–2 yr after cutting with that in mature herb‐rich forests in SW Finland. The total and mean numbers of vascular plant species both in the study areas and in the sample plots, were almost double in clear‐cut areas compared to mature forests. Clear‐cuttings and mature forests were distinctly separated by multivariate analyses (DCA). Several dozen species not found in forests were common in clear‐cut areas. Most of them probably belong to the neglected native species pool of early boreal forest succession and are dependent on the long‐term persistent seed bank or effective wind dispersal. It is emphasized that in forests many plant species are confined to the very early stages (< 2 yr) after disturbance. The storage effect of the long‐term persistent seed bank is crucial for the maintenance of plant diversity in boreal forests. Probably a considerable part of the flora of agricultural areas is composed of species that were originally disturbance dependent forest plants. Scarification is beneficial to disturbance dependent plants and may be useful in restoration of populations of species of early succession.     

种子类别和埋藏深度对雌性小泡巨鼠发现种子的影响

2001年9～12月,在四川省都江堰林区实验围栏内研究了栓皮栎、袍树、栲树、石栎、青冈和油茶种子与6种埋藏深度对小泡巨鼠雌性成体发现埋藏种子的影响。结果表明：1)由于不同种子在种子大小、营养价值和单宁含量等存在差异,雌性小泡巨鼠对个体最大的石栎种子发现率最高,油茶(脂肪含量高)和栲树(单宁含量低)次之,单宁含量较高的袍树、青冈和栓皮栎则较低;2)埋藏深度与雌性小泡巨鼠发现栓皮栎种子的比例呈显负相关,即随着埋藏深度增加,小泡巨鼠发现埋藏种子的比例则减少。     

Long‐term dynamics of winter and summer annual communities in the Chihuahuan Desert

Abstract. Winter and summer annuals in the Chihuahuan Desert have been intensively studied in recent years but little is known about the similarities and differences in the dynamics between these two communities. Using 15 yr of census data from permanent quadrats, this paper compared the characteristics and temporal dynamics of these two distinct, spatially co‐existent but temporally segregated communities. Although the total number of summer annual species recorded during our 15 yr of observation was higher than winter annuals, the mean number of species observed each year was higher in the winter community. The winter community exhibited lower temporal variation in total plant abundance and populations of individual species, lower species turnover rate and higher evenness than the summer community. The rank abundances of species in winter were significantly positively correlated for a period of up to 7 yr while in summer significant positive correlations in rank abundance disappeared after 2 to 3 yr. The higher seasonal species diversity (i.e. number of species observed in each season) in winter rather than the overall special pool (over 15 yr) may be responsible for the greater community stability of winter annuals. The difference in long‐term community dynamics between the two communities of annual plants are likely due to the differences in total species pool, life history traits (e.g. seed size), and seasonal climatic regimes.     

花生种皮蜡质和角质层与黄曲霉侵染和产毒的关系

黄曲霉侵染花生的研究表明,种皮破损的黄曲霉毒素含量显著高于种皮完整的,种皮对黄曲霉侵染和产毒起着重要屏障作用。采用氯仿去除种皮蜡质,用KOH或角质酶去除种皮角质层后,种子黄曲霉感染率和黄曲霉毒素含量显著提高。种皮蜡质和角质层同时去除的与种皮破损的黄曲霉感染率和毒素含量差异不显著,表明种皮的抗性成份主要是蜡质和角质层。种皮蜡质含量测定和种皮表面扫描电镜观察表明,蜡质的含量和角质层的厚度与品种的抗性有关。抗性品种种皮蜡质含量显著高于感病品种。种皮蜡质提取物在体外抑菌效果不显著。说明蜡质的抗性作用主要是物理性阻止黄曲霉菌的穿透。     

Early seedling growth of pine (Pinus densiflora) and oaks (Quercus serrata,Q. mongolica,Q. variabilis) in response to light intensity and soil moisture

In climatic chambers seed germination and seedling growth of Pinus densiflora Sieb. et Zucc., Quercus serrata Thunb., Quercus mongolica Fisch. ex Turcz. and Quercus variablilis Bl. were investigated as functions of light intensity and soil moisture. In Korea these tree species occur widely and form mixed forests with different distributions. Species clearly differed in the pattern of germination and early seedling growth between light and soil treatments. The germination of pine did not differ between the experimental treatments until the breaking of the primary buds. After that, light intensity was the deciding factor for further development. In the most moist treatment (approx. field capacity) growth of the pine seedlings was strongly inhibited. For the three oak species, differences between experimental treatments first occurred after complete formation of primary leaves. Seed development strongly correlated with the weight of the acorn. The large seeded Q. variabilis (acorns with mean weight of 4.7 g) developed faster and reached larger dimensions towards the end of the experiment than Q. mongolica (2.8 g per acorn) and Q. serrata (0.9 g per acorn). Regarding height and biomass growth, the oak species showed a higher shade tolerance than pine. The proleptic shoot growth was clearly influenced by the light intensity. Root formation was favoured by a high exposure to light. In case of the oak species reduction of soil moisture increased the length of primary roots and the number of secondary roots.     

The role of soil seed banks in the restoration of dry acidic dune grassland after burning of Ulex europaeus scrub

Question: Can the seed bank play a significant role in the restoration of plant communities of dry acidic dune grassland where fire has destroyed Ulex europaeus scrub? Location: Northern French Atlantic coast. Methods: One year after the fire, the seed bank and vegetation were sampled in 1 m × 1 m plots along three transects from the oldest scrub vegetation towards the grassland. Differences in species richness, seed density and contribution of ecological groups in the seed bank and vegetation along the transects were analysed. Results: Seed density and species richness in the seed bank decreased significantly from the grassland towards the centre of the scrub vegetation; 50% of the seed bank consisted of core species of the target plant community, such as Carex arenaria, Aira praecox, Rumex acetosella and Agrostis capillaris. Seeds of these species were also found in the deeper soil layers beneath the oldest scrub vegetation, indicating that they can be considered to be long‐term persistent. Beneath the youngest scrub vegetation, seeds of rare satellite target species also occurred. However, no target species were established on the burned site after one year, resulting in a large discrepancy between seed bank and vegetation. Conclusions: Although the seeds present in the soil indicate that restoration of the acidic grassland based on the seed bank is possible, additional management actions such as mowing and soil disturbance may be necessary to restrict resprouting of Ulex and to stimulate the germination of seeds of target species in the deeper soil layers.     

Inheritance of seed dormancy in Cummis sativus var. hardwickii (Royle) Alef.

Summary Reciprocal matings were made between two Cucumis sativus var. sativus L. inbred lines (WI 1606 and WI 2808) and two var. hardwickii (Royle) Alef. accessions (PI 215589 and PI 183967). Each case produced a series of reciprocal F₁, F₂, and BC₁ and BC₂ progenies which were used to evaluate seed dormancy in var. hardwickii. Under controlled conditions (25°±1°C and 85%±5% RH; 12 h fluorescent light, 30 mol s^–1 m^–2), no seed dormancy was observed in the var. sativus inbred lines 36 days following seed extraction from fruit. With rare exception, var. hardwickii accessions were dormant for at least 60 days. Seed dormancy in the F₁ was absent 36 days post extraction, indicating that dormancy in var. hardwickii is conditioned by recessive genes present. Seed of some F₁ progeny germinated between 36 and 50 days post-extraction, indicating the presence of transient dormancy or the more variable expression of the dormancy of var. hardwickii. No significant reciprocal differences in either germination rate or percentage were detected in either of the F₁ and F₂ progeny sets, suggesting lack of cytoplasmic or maternal control over these traits. It was estimated that three to seven factors or loci are involved with the expression of this trait depending on the method of calculation, and that a complex interaction between embryonic and non-embryonic tissue exists. Least square estimates indicate that both additive and dominance effects were important in the expression of dormancy. Comparison of theoretical geometric and arithmetic F₂ means to observed F₂ means also suggests that non-additive gene action contributes substantially to the observed variation. Broad-sense heritability ranged between 78 and 95%.