The role of reproductive phenology, seedling emergence and establishment of perennial Salix gordejevii in active sand dune fields

BACKGROUND AND AIMS: The function of sexual reproduction of perennials in restoration of vegetation of active dune fields frequently has been underestimated. The objective of this study was to evaluate the role of sexual reproduction of the perennial Salix gordejevii in the revegetation of active dunes. METHODS: Seedling emergence and establishment of S. gordejevii were examined both in controlled experiments (germination at different burial depths with different watering regimes) and in field observations in three dune slacks. The reproductive phenology and soil seed bank of S. gordejevii, the dynamics of soil moisture, the groundwater table and the landform level of three dune slacks were monitored. KEY RESULTS: Seeds of S. gordejevii began maturation on 1 May, and seed dispersal lasted from 8 May to 20 May. Seeds on the soil surface germinated significantly faster than those buried in soil (P<0.05). Seedling emergence was negatively correlated with landform level. When most seedlings emerged, there was a significantly positive correlation between soil moisture and seedling emergence (P<0.01). Rainfall was negatively correlated with seedling emergence. Seedling establishment was significantly and positively correlated with seedling emergence (P<0.05), and 72.3 % of the emergent seedlings were established at the end of the growing season. These results indicated that (a) seeds matured and dispersed before the rainy season; (b) seeds germinated as soon as they contacted a moist surface and relied more on soil moisture than on rainfall; and (c) more seedlings emerged at lower sampling points in dune slacks. CONCLUSIONS: In natural conditions, restoration of active sand dune fields generally commences with revegetation of dune slacks where sexual reproduction of perennials contributes greatly to species encroachment and colonization and hence plays an important role in restoration of active dune fields. Furthermore, aeolian erosion in dune slacks, leading to good soil moisture, facilitates seed germination, seedling emergence and establishment of S. gordejevii.     

The role of seed limitation and resource availability in the recruitment of native perennial grasses and exotics in a South Australian grassland

Abstract We investigated what factors lead to invasion of exotics or re‐colonization of native perennial grasses in the South Australian mid‐north grasslands. We manipulated 160 experimental quadrats by clipping, irrigation and seed addition and assessed recruitment by exotics in an area dominated by perennial grasses and perennial grass recruitment in an area dominated by exotics. Treatment effects differed with season for exotics: their biomass increased with irrigation in autumn and seed addition in winter. However, in both periods other factors, probably soil properties, also had a strong effect. We detected no perennial grass seedlings in the quadrats over 1 year, possibly due to unsuitable environmental conditions or persistent high competition levels. Under controlled conditions the presence of the invasive annual Avena barbata had a strong negative effect on the recruitment of the native perennial Austrodanthonia caespitosa at any moisture and nutrient availability. Avena also germinated faster and more frequently than Austrodanthonia, especially at low soil moisture. During an imposed drought Austrodanthonia seedlings survived longer in the absence of Avena. The results suggest that annual exotics are highly responsive to resources and can quickly invade areas, while the re‐colonization of invaded areas by native grasses requires a complex (and less likely) rainfall regime.     

Seed and Seedling Susceptibility to Phased Moisture Stress in Soil

Seeds of calabrese and carrot treated with fungicide were sownin soil at three levels of moisture stress causing a range ofeffects on seed germination or seedling emergence. After periodsof up to 3 weeks the soil was either rehydrated directly, orrehydrated after a short period of severe dehydration. Seedand seedling losses appeared to be almost entirely due to seedlingdeath after germination in the conditions of severe dehydration,but even then some germinated seeds survived these conditions.Seed deterioration or death was implicated only in carrot whenseeds were dehydrated after being held for from 1 to 3 weeksin soil at —10 ? 10⁵ Pa. A model for seed moisture effectson deterioration and survival is proposed.     

Salt tolerance of Triticum monococcum L., T. dicoccum (Schrank) Schubl., T. durum Desf. and T. aestivum L. seedlings

Responses to salt stress of diploid wheat Triticum monococcum L., tetraploid wheats T. dicoccum (Schrank) Schubl. and T. durum Desf. cv. Grandur, and hexaploid wheats T. aestivum L. cvs. Begra and Gama were studied. Seeds were germinated on filter paper in Petri dishes, moistened in Hoagland medium containing 0 (control), 10, 20, 50, 100 and 200 mM NaCl. Index of tolerance to salt treatments was calculated on the basis of shoot length. Increase in salt concentration led to decrease in seed germination and inhibition of shoot and root elongation. Hexaploid and diploid wheats were more tolerant to salt stress than tetraploid wheats.     

Effects of time of application of Ethrel on male sterility and ear emergence in wheat Triticum aestivum

The induction of male sterility in wheat by application of Ethrel at different concentrations and times was investigated in glasshouse-grown Triticum aestivum cv. Sirius. The results obtained agree with our previous findings, that to induce full sterility, Ethrel must be applied before meiosis is initiated in the oldest florets of the ear. However, to ensure full emergence of sterilized ears, the application has to be made as close to this stage as possible using a concentration of between 1000 and 2000 ppm. Ethrel application thus shows promise as a method for detecting heterotic combinations by producing sufficient F ₁ seed for small-scale field trials.     

冷蒿草原土壤可萌发种子库特征及其对放牧的响应

（１）采用萌发试验法对内蒙古冷蒿（Ａｒｔｅｍｉｓｉａ ｆｒｉｇｉｄａ）草原土壤种子特征及其在不同放牧压力下的变化进行了研究。（２）冷蒿草原可萌发种子库由４种多年生禾草,１１种种多年生杂草及３种１年生植物所组成。（３）每样中的可萌发种子是变化于４５到３０５之间,平均１０２／样。多年生禾草、多年生杂类草及１年生植物的土壤中种子量分别占总可萌发种子库的４６．５７％、５１．９６％和１．５７％。多年和禾 草     

Crop seed spillage along roads: a factor of uncertainty in the containment of GMO

Feral populations of crop species along roadsides contribute to the uncertainty regarding the containment of genetically modified (GM) crops, as the feral populations could promote the persistence of transgenes outside of cultivated fields. Roadside populations of several common crop species are known to occur far from arable fields, and the dispersal pathways that promote their recruitment in road verges are unclear. Human-aided dispersal, in particular adhesive dispersal by vehicles, has been suggested as a possible vector, but this has not yet been proven experimentally. We sampled the seed rain from vehicles inside two motorway tunnels in an urban environment to reveal the contribution of crop species to seeds unintentionally dispersed by traffic beyond agricultural production areas. Three species of arable crops, wheat Triticum aestivum , rye Secale cereale and oilseed rape Brassica napus , were among the most frequent species deposited by vehicles inside the motorway tunnels. Each of the three species was clearly more predominant in one direction of traffic. While seeds of Triticum aestivum and Secale cereale were primarily transported into the city, Brassica napus was significantly more abundant in samples from lanes leading out of the city. Seed sources in the local surroundings of the tunnels were virtually nonexistent, and the high magnitude of seed deposition combined with high seed weights suggests a dispersal mechanism different from other species in the sample, at least for Triticum aestivum and Secale cereale . This provides evidence that spillage during transport is a major driver for long-distance dispersal of crops. Our results suggest that seed dispersal by vehicles is the major driver in the recruitment of roadside populations of arable crops, providing a possible escape route for GM crops. Risk management should thus aim at curbing transport losses of GM crops.     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

Primary structure, recombinant expression, and molecular characterization of Phl p 4, a major allergen of timothy grass (Phleum pratense)

Grass pollen allergy is one of the most important allergic diseases world-wide. Several meadow grasses, like timothy grass and rye grass, contribute to allergic sensitizations, but also allergens from extensively cultivated cereals, especially rye, make a profound contribution. The group 4 allergens are well known as important major allergens of grasses. We have cloned for the first time group 4 sequences from Phleum pratense, Lolium perenne, Secale cereale, Triticum aestivum, and Hordeum vulgare, and investigated the IgE-reactivity of recombinant Phl p 4 as a candidate for allergy diagnostic and therapeutic applications.     

Seed regeneration potential of canopy gaps at early formation stage in temperate secondary forests, Northeast China

Promoting the seed regeneration potential of secondary forests undergoing gap disturbances is an important approach for achieving forest restoration and sustainable management. Seedling recruitment from seed banks strongly determines the seed regeneration potential, but the process is poorly understood in the gaps of secondary forests. The objectives of the present study were to evaluate the effects of gap size, seed availability, and environmental conditions on the seed regeneration potential in temperate secondary forests. It was found that gap formation could favor the invasion of more varieties of species in seed banks, but it also could speed up the turnover rate of seed banks leading to lower seed densities. Seeds of the dominant species, Fraxinus rhynchophylla, were transient in soil and there was a minor and discontinuous contribution of the seed bank to its seedling emergence. For Quercus mongolica, emerging seedling number was positively correlated with seed density in gaps (R?=?0.32, P<0.01), especially in medium and small gaps (<500 m(2)). Furthermore, under canopies, there was a positive correlation between seedling number and seed density of Acer mono (R?=?0.43, P<0.01). Gap formation could promote seedling emergence of two gap-dependent species (i.e., Q. mongolica and A. mono), but the contribution of seed banks to seedlings was below 10% after gap creation. Soil moisture and temperature were the restrictive factors controlling the seedling emergence from seeds in gaps and under canopies, respectively. Thus, the regeneration potential from seed banks is limited after gap formation.     

The Potential for Newly-Germinated Cabbage Seed Survival and Storage at Sub-Zero Temperatures

The moisture content of newly germinated cabbage seed (radicles1 05 mm long) was reduced to 14% of f.wt without loss of viability.As the moisture content was reduced below 45%, the temperatureat which the germinated seeds froze, and therefore died, decreasedprogressively to a minimum of –34 C at 19% moisture content.No freezing exotherms were recorded in seeds with moisture contentsbelow 19%. Seeds with a moisture content between 14 and 16%maintained viability for at least 1 week when cooled at 26C.min^–1to –20 C and held at this temperature, indicating thepotential for prolonged storage of these low-moisture-contentgerminated (LMCG) seeds. Brassica oleracea, cabbage, germinated seed, seed storage, fluid drilling, freezing exotherm, thermal analysis     

黄土高原半干旱偏旱区草粮轮作田土壤水分恢复效应模拟

采用实地调查和EPIC模型相结合的方法,模拟研究了黄土高原半干旱偏旱区不同草粮轮作模式的土壤水分恢复效应.结果表明：多年生苜蓿地和苜蓿翻耕后种植粮食作物农田0～10 m土层土壤湿度调查值与模拟值间的相关系数均超过0.9（P<0.01）,相对均方根误差在0.05～0.16,相对误差均低于10%;模拟与实测的土壤湿度剖面分布变化趋势一致.在黄土高原半干旱偏旱区,苜蓿地深层土壤干层恢复难度较大,在种植苜蓿期间应避免8～10 m土层土壤湿度降到5.7%以下.苜蓿地适宜种植年限为4～6 a,最长不应超过8 a.苜蓿翻耕后适宜采用马铃薯→马铃薯→春小麦轮作模式进行土壤水分恢复,32～33 a后可以再次种植苜蓿.     

Effects of ungulates and prairie dogs on seed banks and vegetation in a North American mixed-grass prairie

The relationship between vegetation cover and soil seed banks was studied in five different ungulate herbivore-prairie dog treatment combinations at three northern mixed-grass prairie sites in Badlands National Park, South Dakota. There were distinct differences in both the seed bank composition and the aboveground vegetation between the off-prairie dog colony treatments and the on-colony treatments. The three on-colony treatments were similar to each other at all three sites with vegetation dominated by the forbs Dyssodia papposa, Hedeoma spp., Sphaeralcea coccinea, Conyza canadensis, and Plantago patagonica and seed banks dominated by the forbs Verbena bracteata and Dyssodia papposa. The two off-colony treatments were also similar to each other at all three sites. Vegetation at these sites was dominated by the grasses Pascopyrum smithii, Bromus tectorum and Bouteloua gracilis and the seed banks were dominated by several grasses including Bromus tectorum, Monroa squarrosa, Panicum capillare, Sporobolus cryptandra and Stipa viridula. A total of 146 seedlings representing 21 species germinated and emerged from off-colony treatments while 3069 seedlings comprising 33 species germinated from on-colony treatments. Fifteen of the forty species found in soil seed banks were not present in the vegetation, and 57 of the 82 species represented in the vegetation were not found in the seed banks. Few dominant species typical of mixed-grass prairie vegetation germinated and emerged from seed banks collected from prairie dog colony treatments suggesting that removal of prairie dogs will not result in the rapid reestablishment of representative mixed-grass prairie unless steps are taken to restore the soil seed bank.     

小麦族遗传资源的多样性及其保护

禾木科小麦族中包含了三种世界最重要的粮食作物,即：小麦、大麦和黑麦以及许多具有重要经济价值的牧草种类。小麦族植物种类繁多、分布广泛、生态多样,具有极其丰富的形态和遗传变异类型。作为巨大的基因资源库,小麦族植物在通过现代生物技术而导入外源有益基因的麦类作物育种程序中,具有重要和特殊的价值。然而对于小麦族植物的生物多样性的研究和了解还远远不足。同时在全球环境的不断改变和遭到破坏的今天,一些小麦族的物种已处于濒危的状态而面临灭绝,因此对于小麦族丰富的遗传多样性制定有效的措施进行保护是摆在我们面前亟待解决的课题。     

Response of wheat genotypes to sowing date and boron fertilization aimed at controlling sterility in a rice-wheat rotation in Nepal

Spikelet sterility in wheat (Triticum aestivum L.) is emerging as a production threat in different parts of Nepal. This study was aimed at determining the effects of sowing date and boron application in controlling spikelet sterility in four different genotypes of spring wheat in a rice-wheat system in the western hills of Nepal. Four genotypes of known different responses to boron were planted on 21 November, 6 December and 21 December, 1994 with or without boron application at 1 kg B ha-1 (i.e. 9 kg borax ha-1) on a soil that was known to be deficient in boron.The effect of sowing date was significant for the phenology, yield components, percentage sterility and grain yield. Sterility was significantly increased in the crop planted on 21 December, which had also the lowest 1000 seed weight and grain yield; there was an almost 50% grain yield reduction compared to the crop planted on 21 November. Terminal moisture stress (i.e. lack of moisture during the later part of the development) was observed in the late sown crop which also amplified the extent of sterility associated with boron deficiency. Genotypes differed in response to sowing dates and boron treatment for all of the phenological events measured, yield components, grain yield and percentage sterility. SW-41 and BL-1022 had significantly higher sterility at all sowing dates. BL-1249 showed a consistently lower% sterility over all sowing dates and boron treatments. The addition of boron significantly increased the number of grains set per spike thereby decreasing the total sterility in boron responsive genotypes SW-41 and BL-1022 while those not susceptible did not respond. The boron concentration in the flag leaf at anthesis was increased in treatments with added B in the soil but genotypes did not differ in boron concentration for any soil treatment.     

The 120-yr period for Dr. Beal's seed viability experiment

After 120 yr of burial in moist, well-aerated sand, 23 seeds of Verbascum blattaria and two seeds of a Verbascum sp. germinated and produced normal plants (50% germination for Verbascum). After a 6-wk cold treatment, a single seed of Malva rotundifolia germinated also, producing a normal plant (2% germination). Plants were grown to maturity in a greenhouse, and flowering was induced by exposure to a 6-wk cold treatment. Flowers were artificially pollinated to produce seed of both Verbascum blattaria and Malva rotundifolia. The Verbascum sp. failed to set seed. Collected seeds were subsequently germinated, producing normal plants. F(1) seeds of V. blattaria had a germination of 64%. Seeds (6%) of M. rotundifolia germinated after a cold treatment.     

Native perennial grasses show evolutionary response to Bromus tectorum (cheatgrass) invasion

Invasive species can change selective pressures on native plants by altering biotic and abiotic conditions in invaded habitats. Although invasions can lead to native species extirpation, they may also induce rapid evolutionary changes in remnant native plants. We investigated whether adult plants of five native perennial grasses exhibited trait shifts consistent with evolution in response to invasion by the introduced annual grass Bromus tectorum L. (cheatgrass), and asked how much variation there was among species and populations in the ability to grow successfully with the invader. Three hundred and twenty adult plants were collected from invaded and uninvaded communities from four locations near Reno, Nevada, USA. Each plant was divided in two and transplanted into the greenhouse. One clone was grown with B. tectorum while the other was grown alone, and we measured tolerance (ability to maintain size) and the ability to reduce size of B. tectorum for each plant. Plants from invaded populations consistently had earlier phenology than those from uninvaded populations, and in two out of four sites, invaded populations were more tolerant of B. tectorum competition than uninvaded populations. Poa secunda and one population of E. multisetus had the strongest suppressive effect on B. tectorum, and these two species were the only ones that flowered in competition with B. tectorum. Our study indicates that response to B. tectorum is a function of both location and species identity, with some, but not all, populations of native grasses showing trait shifts consistent with evolution in response to B. tectorum invasion within the Great Basin.     

Effects of temperature and storage length on seed germination and the effects of light conditions on seedling establishment with respect to seed size in Ligularia virgaurea

Ligularia virgaurea is widely distributed in the alpine meadows of the eastern Qinghai-Tibet plateau. We studied the effects of temperature and seed storage length on seed germination in a laboratory experiment, the effects of seed mass and light intensity on seed emergence in a pot experiment, and the effect of meadow disturbance intensity on seed emergence in a field experiment. Our results showed that seeds of L. virgaurea germinated well under a wide range of temperatures. Germination percentage decreased with increased seed storage length. When seeds were stored for either 6 or 12 months the germination percentage increased with decreasing temperature. The emergence percentage of large seeds was higher than that of small seeds. Seedling survival of large seeds was greater than that of small seeds in 75% and 50% of natural irradiance. Large seeds of L. virgaurea were more successful colonizers in the alpine meadows. Seeds of L. virgaurea germinated in both disturbed meadows and non-disturbed meadows, but seed emergence and seedling establishment were higher in the disturbed meadows, that is, disturbance could facilitate the recruitment and establishment of L. virgaurea .     

三江平原恢复湿地土壤种子库特征及其与植被的关系

通过幼苗萌发法和样方调查相结合的方法对三江平原不同演替恢复阶段的种子库特征及其与植被的关系进行了研究。将开垦湿地、不同演替恢复阶段湿地以及天然湿地不同土壤层次(0-5、5-10 cm和根茎)的种子库在两种水分条件下(湿润、淹水10 cm)进行萌发处理。结果表明: 随着演替恢复阶段的进行, 种子库的结构和规模逐渐扩大, 地表群落表现出由旱生物种占优势的群落逐渐演变成以小叶章(Calamagrostis angustifolia)占优势的湿生群落的演替趋势。恢复7年湿地、恢复14年湿地、天然湿地土壤种子库萌发物种数分别为24种、29种、39种, 植被物种数为21种、25种、14种。湿地类型、水分条件和土壤层次均显著影响种子库萌发的物种数及幼苗数(p < 0.01)。种子库具有明显的分层现象, 天然湿地0-5 cm土层种子库种子萌发密度是5-10 cm土层的4倍左右, 而恢复湿地仅1.3倍左右, 且土层间萌发物种相似性系数较低。湿润条件下的萌发物种数显著高于淹水条件, 且两种水分条件下萌发物种的生活型不同。由于恢复时间较短, 不同演替恢复阶段的种子库与植被相似性维持在30%以下。湿地中根茎分蘖出大量的湿地物种, 对于小叶章等优势物种的繁殖具有重要作用。研究表明, 在开垦湿地退耕后的次生演替阶段, 种子库能够保持大量的湿地物种, 通过对湿地种子库与植被的关系研究, 能够为三江平原湿地群落演替与湿地恢复提供策略指导。     

Effect of seed position in spikelet on life history of Eremopyrum distans (Poaceae) from the cold desert of north-west China

Background and Aims

Most studies on seed position-dependent effects have focused on germination characteristics. Our aim was to determine the effects of seed position in the spikelet on differences in timing of germination and on the ecological life history of the grass Eremopyrum distans in its cold desert habitat.

Methods

For seeds in three spikelet positions, morphology, mass and dormancy/germination characteristics were determined in the laboratory, and seeds planted in field plots with and without watering were followed to reproduction to investigate seedling emergence and survival, plant size and seed production.

Key Results

After maturation, of the seeds within the spikelet, basal ones (group 1) are the largest and have the highest proportion with physiological dormancy, while distal ones (group 3) are the smallest and have the highest proportion of non-dormant seeds. A higher percentage of seeds after-ripened in groups 2 and 3 than in group 1. Seeds sown in the field in early summer and watered at short, regular intervals germinated primarily in autumn, while those under natural soil moisture conditions germinated only in spring. Both cohorts completed their life cycle in early summer. Seeds in group 1 had lower percentages of seedling emergence and higher percentages of seedling survival than those in groups 2 and 3. Also, plants from group 1 seeds were larger and produced more seeds per plant than those from groups 2 and 3.

Conclusions

Seed position-dependent mass was associated with quantitative differences in several life history traits of E. distans. The environmentally enforced (low soil moisture) delay of germination from autumn to spring results in a reduction in fitness via reduction in number of seeds produced per plant.