Tumbleweeds in the Western Australian cropping system: seed dispersal characteristics of Salsola australis

Salsola australis, like other agricultural weed species of the Salsola genus, produces a mobile seedbank. Aspects of this mobile seedbank were investigated in three field trials, including total seed production, rate of seed shedding, rate at which seeds lose germinability and the distance and directionality of plant movement. Total seed production was highly variable (ranging from 138 to 7734 seeds per plant), but was directly related to aboveground plant biomass at maturity. Following senescence, mature plants broke free of their root system and the wind driven plants moved considerable distances (1.6–1247.2 m). Half of the mobile plants moved <100 m, as they became entangled with other S. australis plants within the stand. Seed shedding commenced before the plants became mobile and increased with movement, but was also related to the aging and weathering processes experienced by stationary or mobile plants. All plants retained a proportion of their seed in spite of movement, weathering and ageing of the plants, although germinability of retained seed dropped to <2% after 2 months. Salsola australis engages in broad scale seed dispersal similar to that observed in other species of the Salsola genus, allowing this species to maintain a high rate of invasion and range expansion.     

种子传播提高生物多样性的机制

种子是保存物种遗传信息的载体,保护种子资源是植物保护和生物多样性保护的重要内容。种子传播不仅对保护植物自身的繁殖和生存至关重要,而且对群落稳定甚至生态系统功能具有重要意义。该文综述了种子传播的方式、干扰因素以及种子传播通过提高生物多样性来促进植物保护的机制,即丰富的生物多样性降低了病虫害对植物的危害。种子传播易受人为活动和气候变化等因素干扰传播媒介和破坏生境;需要采取构建廊道等措施来降低因生境破碎化引起的负面影响。种子传播提高生物多样性的机制主要通过增加基因交流来提高遗传多样性,通过增加种子扩散效率和存活率等来提高物种多样性、稳定群落结构和通过连通生境斑块来提高生态系统多样性。因此,构建基于生态系统的种子传播网络对保护生物多样性具有重要意义。     

The ecological role of dew in assisting seed germination of the annual desert plant species in a desert environment,northwestern China

It is important to understand the effects of dew events on non-mucilaginous seed germination of annual desert plant species during dry seasons, which is critical to maintaining long-term soil seed banks in a harsh desert environment. We hypothesize that dew deposition also assists in the non-mucilaginous seed germination of annual desert species. A common field dew treatment experiment was conducted in the Linze Inland River Basin Research Station to investigate the effects of dew deposition on the seed germination of four annual species, including Agriophyllum squarrosum, Corispermum mongolicum, Bassia dasyphylla and Halogeton arachnoideus. The results showed that the presence of dew significantly increased seed germination percentages and decreased the nonviable seed percentages of B. dasyphylla and H. arachnoideus, whereas there was no such trend for the seeds of C. mongolicum and A. squarrosum. The ecological effects of dew on the seed germination and viability of the annual desert plants were species specific. Although dew wetting is insufficient to cause seed germination, it may help in priming the seeds.     

古尔班通古特沙漠不同类型生物结皮对草本植物多样性影响

选择古尔班通古特沙漠的北部(一号点)、中部(二号点)、南部(三号点)3个不同样点的裸沙和藻结皮、地衣结皮与苔藓结皮3种生物结皮类型,对比研究了草本植物多样性的差异性及其主要环境影响因素。结果表明:(1)不同生物结皮类型的土壤理化性质有明显差异,土壤有机质、全氮、全磷、全钾含量以及黏粒、粉粒和细沙的含量随生物结皮演替显著上升,而中沙和粗沙的含量呈显著下降趋势,在沙漠不同区域呈现明显的空间异质性,二号样点中裸沙和藻结皮的养分含量和pH明显低于一号点和三号点。(2)草本植物的物种丰富度和Shannon-Wiener指数随生物结皮发育呈明显上升趋势,草本植物的物种组成、群落结构在不同类型生物结皮和沙漠不同区域均具有显著差异。(3)在土壤理化特征中,有机质、速效P和全K含量,以及pH和粉粒含量是影响草本植物分布的关键因子。(4)不同类型生物结皮之间的微地形和种类组成差异、种子生物学特性以及生物结皮在不同尺度下的土壤环境异质性共同影响草本植物在生物结皮中的物种组成和丰度,最终导致草本植物群落结构在生物结皮中的演替变化。     

古尔班通古特沙漠羽毛针禾（Stipagrostis pennata）种群种子雨特征

通过布设种子收集器收集种子,对收集的种子以时空差异进行分组分析,探讨羽毛针禾[WTBX]（Stipagrostis pennata）[WTBZ]种子散布规律以及古尔班通古特沙漠种群的种子雨特征。结果表明：① 羽毛针禾种子雨的积累密度平均达到3 766.30粒·株-1,其中饱满种子占19.56%;② 种子散布的高峰集中在6月25到7月15日,其落种量占整个种子雨的61.96%,其后种子雨密度随时间逐渐减小;③ 种子雨密度与生境之间均不存在显著性差异;④ 种子雨总量与其年龄之间存在显著性差异;⑤ 种子雨的前扩散过程中种子集中降落在背风方向4 m范围和株丛周围1 m内。古尔班通古特沙漠南缘种子雨虽质量不高,但密度大,对种群的自然更新具有一定的意义。     

Growth and reproductive success of the seed‐derived plants of Sagittaria trifolia emerging at different times

In order to clarify the growth and reproductive success of seed‐derived Sagittaria trifolia individuals emerging at different times within a season, seeds were sown on May 16, June 16 and July 22 2010 and allowed to grow in pots under shaded and unshaded conditions. The timing of when the first inflorescence of each seedling appeared was recorded, as well as the number of seeds and tubers produced and the dry weight of each organ. In total, 220 seedlings were used, 23–59 in each treatment. As the sowing time was delayed, so too was the appearance of the first inflorescence. Additionally, the number of inflorescences, fruits and seeds produced by the unshaded plants significantly decreased with the sowing time. The total dry weight was significantly greater in the unshaded than in the shaded plants: the July‐sown, shaded plants grew very poorly. The relative resource allocation to the tubers was greater in the late‐emerging, shaded seedlings. Even in the shaded groups, except for the July‐sown plants, most of the plants set seed. Therefore, when addressing weed control in paddy fields, one should keep seedlings in mind, in addition to plants that have grown from tubers.     

Spatial distribution of Lolium rigidum seedlings following seed dispersal by combine harvesters

This paper considers the relationships between the dispersal of seeds and the distribution pattern of an annual weed. A comparative study of seed dispersal by combine harvesters, with and without a straw chopper attached, was established using Lolium rigidum, a common weed in Mediterranean cereal crops. Seed dispersal distance was quantified and the relationships between dispersal and fine‐scale seedling distribution evaluated. Primary dispersal of L. rigidum seeds occurs in a very limited space around the parent plants, but the density of seed is low because most seeds do not fall from spikes spontaneously. In contrast, many seeds are spread by combine harvesters. In this study the maximum dispersal exceeded 18 m from established stands in cereal fields, although the modal distance was close to the origin. In addition, the action of the combine harvesters tended to accumulate L. rigidum seeds predominantly under the straw swath, with some lateral movement. This action could explain the fine‐scale banded pattern of L. rigidum in cereal fields. Although the treatment of straw by the standard and straw chopper combines differed, the resultant seed distribution showed few differences.     

Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditions

This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage ( Brassica pekinensis ). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r ² of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants.     

Effects of water stress and NaCl stress on different life cycle stages of the cold desert annual Lachnoloma lehmannii in China

For a plant species to complete its life cycle in arid and saline environments, each stage of the life cycle must be tolerant to the harsh environmental conditions. The aim of the study was to determine the effects of water stress (water potentials of -0.05, -0.16, -0.33, -0.56, -0.85 and -1.21 MPa) and NaCl stress (50, 100, 200, 300, 400, 500 and 600 mmol/L NaCl) on seed germination percentage, seedling survival and growth, juvenile growth and plant reproduction of Lachnoloma lehmannii Bunge (Brassicaceae), an cold desert annual that grows in the Junggar Basin of Xinjiang, China in 2010. Results indicated that low water stress (-0.05 and -0.16 MPa) had no significant effect on seed germination percentage. With a decrease in water potential, germination percentage decreased, and no seeds germinated at -0.85 and -1.21 MPa water stresses. Germination percentage of seeds was significantly affected by NaCl stress, and higher germination percentages were observed under non-saline than saline conditions. An increase in NaCl concentrations progressively inhibited seed germination percentage, and no seeds germinated at ≥400 mmol/L NaCl concentration. Non-germinated seeds were transferred from both PEG (polyethylene glycol-6000) and NaCl solutions to distilled water for seed germination recovery. The number of surviving seedlings and their heights and root lengths significantly decreased as NaCl stress increased. About 30% of the plants survived and produced fruits/seeds at 200 mmol/L NaCl concentration. Thus, seed germination, seedling establishment and reproductive stage in the life cycle of L. lehmannii are water- and salt-tolerant, with seedlings being the least tolerant. These tolerances help explain why this species can survive and produce seeds in arid and saline habitats.     

Assessing wind and mammals as seed dispersal vectors in an invasive legume

While some plants have modified seed structures to facilitate dispersal, many lack such specialised adaptations, making their mode of dispersal unclear. This can be particularly problematic for predicting shifts in species ranges or tracking the spread of invasive plants. As an example, the seed size and shape of the invasive legume, Lespedeza cuneata, suggest that wind and attachment to animals are not important for dispersal, yet populations can spread surprising distances within a few years. Using a series of experiments conducted in the laboratory and field, we tested wind and mammal fur as mediators of seed dispersal. To test wind dispersal, seed traps were arranged radially around a patch of L. cuneata and seeds were collected following dispersal. Attachment to mammal fur was tested by fitting pelts of a deer, coyote and raccoon to artificial torsos and determining seed retention in both the field and the laboratory. Laboratory trials also examined the influence of wet versus dry conditions. Our results showed that wind direction strongly influenced dispersal distance and seeds were readily dispersed by mammal fur. The number of seeds retained was species specific, depending on fur depth and mammal size, with seed retention increasing under wet conditions. Together, these results suggest that both wind and mammal fur contribute to the movement of L. cuneata across grasslands. Consequently, both dispersal vectors should be considered when designing and implementing control strategies.     

温带荒漠珍稀濒危植物的引种栽培

我国荒漠大部分属温带荒漠,以干旱、风沙、盐碱、粗瘠和植被稀疏为主要特征。植物种类约有1000余种[1],其中不乏特有种和稀有植物种。与其它地区植物种类一样,随着自然生境的逆转和人类活动范围扩大,不少种濒临灭绝状态。改善自然生态环境,减少人为破坏,就地保护植物种质资源的流失,需通过建立自然保护区加以实现,而迁地保护濒危植物并开展必要的研究、种质保存和繁殖工作,协助自然界保存濒危稀有植物,并为栽培的濒危植物再转入自然生境提供科学依据、繁殖技术和苗木,则是植物园在植物多样性保护工作中的重要任务。     

荒漠区一年生植物层片的组织格局与生态适应模式

在阿拉善荒漠及其邻近地区 ,有多种一年生植物种群可组成荒漠与绿洲生态系统的恒有性植物层片。本项研究利用样地调查与统计资料 ,取得了多种一年生植物层片物种组成的研究结果 ;在吉兰泰盐湖地区、腾格里沙漠东南部、雅布赖低山区、孪井滩地区、祁连山山麓、额济纳绿洲等地 ,对一年生植物种群生物产量的季节与年度间的波动性进行了调查和测定 ,并与相关的气象资料做了比对分析 ,获得了气候年、季变化与一年生植物层片动态的相关性认识。据此 ,划分了一年生植物层片的生态类型。荒漠与绿洲生态系统中 ,主要的一年生植物层片有 :.荒漠夏雨型一年生禾草类植物层片 ,荒漠一年生杂草类植物层片 ,沙漠一年生沙生植物层片 ,盐漠一年生盐生植物层片 ,绿洲草甸一年生植物层片 ,绿洲胡杨林一年生植物层片 ,柽柳灌丛一年生植物层片 ,绿洲农田一年生杂草植物层片等。多数一年生植物种是在荒漠优势植物株丛间的裸斑土壤种子库中 ,有丰富的种子储备 ,利用夏季较为集中的降雨迅速萌发生长到结实 ,完成一个短暂的生活周期。也有些一年生植物在沙质土、盐渍土、草甸土等特异性生境中各自具有有效的生态适应机制 ,组成沙漠、盐漠、绿洲林地与草地的一年生植物层片。这些一年生植物层片的组织格局 ,生态适应模式 ,生态功能     

Secondary dispersal, spatial dynamics and effects of herbicides on reproductive capacity of a recently introduced population of Bromus sterilis in an arable field

An arable field was subdivided and subjected to either deep inversion ploughing or non‐inversion cultivation after viable seeds of Bromus sterilis had been sown into oilseed rape stubble. After sowing in isolated plots distributed within the field, sequences of cropping treatments for the establishment of two successive winter wheat crops were applied. Each subfield was split into an uphill and a downhill direction for soil cultivation. The field had a 10° slope. In the season following seed introduction, 2.6% of the introduced seeds had successfully germinated and established in the non‐inversion cultivation regime, when no effective graminicide was applied. Ploughing eradicated B. sterilis. Using differential global positioning system (DGPS) mapping of the whole field population, emerged plants were observed up to 8.7 m (uphill treatment) and 21.3 m (downhill treatment) of their initial source. The median distance seeds were transported was 2.3 m uphill and 4.8 m downhill. Post‐emergence application of the herbicide propoxycarbazone slightly reduced weed density and seed weight, and almost halved weed seed production. Application of fenoxaprop‐P‐ethyl was followed by higher density of plants, tillers and seeds of B. sterilis. Seed viability was unaffected by herbicide use. Thus, in the second wheat crop following seed rain, the weed population was dispersed more widely in the field, such that 20–30% of seeds were dispersed more than 5 m distance from the first year's foci of infestation. The relevance of soil cultivation to secondary dispersal of B. sterilis is discussed.     

Analysis of the seed dispersal patterns of wild soybean as a reference for vegetation management around genetically modified soybean fields

There are concerns that genetically modified soybean might threaten the genetic diversity of the wild soybean populations that are distributed in East Asia because genetically modified soybean has no crossing barrier with wild soybean. A simple and effective method to prevent hybridization via pollen flow is spatial separation between the two species because their hybridization occurs only when they grow in close proximity. Therefore, the invasiveness of wild soybean needs to be known in order to secure the appropriate distances. As wild soybean seeds are dispersed mechanically by pod dehiscence, an experiment was conducted in which white sheets were placed on the ground, concentric circles were drawn around the parent plants, and the number of dispersed seeds within each 0.5 m‐wide zone were counted. About 40% of the produced seeds were dispersed and the number of dispersed seeds gradually declined as the distance from the parent plants increased. The model that explained the relationship between the number and distance of the dispersed seeds was produced by using a generalized linear model procedure. More than 95, 99, and 99.9% of the produced seeds stayed within 3.5, 5.0, and 6.5 m after natural pod dehiscence. Knowing these values is useful for evaluating the level of invasive risk by mechanical seed dispersal. The goal of the work is to efficiently and deliberately prevent hybridization by isolating genetically modified soybean fields and wild soybean populations by vegetation management, including weeding and setting up specific‐width buffer zones.     

苦豆子种子特性与种群扩展关系的研究

苦豆子(Sophora alopecuroides L.)种子体积大,千粒重达21.6g。种皮较厚,制约了种子的萌发,采用浓硫酸浸种和机械磨损破坏种皮明显提高了萌发率。种子散布主要依靠自身重力,其散布格局是聚集型散布,多分布在母株周围,为该区域的种子库提供较多的种质资源。此外,还有动物散布和水力作用的散布,使种子能传播较远的距离,同时种子被采食后,通过消化道的磨损使种皮的通透性提高,促进了种子的萌发。     

Demography of Salsola australis populations in the agricultural region of south-west Australia

Salsola australis is a widespread annual weed of broad-scale cropping and pasture systems throughout Australia, and is of concern in the wheat belt of Western Australia. The population dynamics of S. australis was monitored at four sites in the Lake Grace district of Western Australia. At all sites, two to three cohorts emerged in summer and autumn or winter. While initial seedling density varied, density-dependent mortality ensured that the total number of senesced plants at each site was not significantly different. Estimated seed production ranged from 95 to 19 596 seeds per plant, although seed viability was low (approximately 9% for seeds that were shed and 15% for seeds that were retained on the mature plants). Total annual seed production per unit area was highly variable within sites but was not significantly different between sites. These data will facilitate the development of improved control strategies for S. australis .     

散枝猪毛菜的果实多型性及个体大小依赖的繁殖输出

对散枝猪毛菜在自然种群中的个体大小、结实和萌发特性进行了观察。结果表明:①自然种群中,散枝猪毛菜具有大小不同的个体,其在植物体干重、株高、分枝级数、节数上具有显著差异,其个体大小表现出极大的可塑性;②散枝猪毛菜产生4种不同类型的果实(种子),并具有不同的萌发行为和散布特性;③依据个体大小的变化,4种类型的果实在植株上的比例发生了显著变化;随着植物个体的增大,A型果实所占比例逐渐增多,由2.253%增加到24.116%,B型果实所占比例逐渐增多,由6.026%增加到41.307%,C型果实所占比例逐渐减少,由81.561%减少到17.709%,D型果实所占比例逐渐增多,由8.077%增加到17.087%。总之,散枝猪毛菜个体大小的表型可塑性和果实多型性是对荒漠异质环境的一种适应。     

The influence of interspecific interference on the seed production of Stellaria media and Hordeum vulgare (volunteer barley)

The effects of the density and proportion of both volunteer barley ( Hordeum vulgare L.) and Stellaria media (L.) Vill. (common chickweed) on the seed yield of both species was investigated in linseed ( Linum usitatissimum L.) and autumn-sown field bean ( Vicia faba L.). A model was created to estimate these effects. It was a combination of two models. The first was a simple linear model relating weed seed number m² to weed dry weight m². The second was an inverse linear model relating weed dry weight per plant to weed density. A very good relationship existed between barley dry weight and number of seeds m² and between S. media dry weight and number of seed capsules m². This relationship was relatively consistent between experiments. The inverse linear model provided a good estimation of the relationship between weed density and weed dry weight per plant for both barley and S. media . Model variables, however, differed between experiments. Using the combined model it was estimated that, in the absence of other weed species and at a density of 800 plants m², S. media would produce between 4000 and 48 000 seeds m², whereas volunteer barley, at a density of 400 plants m², would produce between 2000 and 8000 seeds m². The presence of barley always reduced S. media seed yield and a barley population of 100 plants m² could reduce S. media seed yield by up to 79%. The presence of S. media reduced barley seed yield in only one of three experiments, in which a S. media density of 800 plants m² reduced barley seed yield by up to 68%. It was concluded that interspecific weed competition should not be ignored as a factor in models of weed population dynamics     

Establishment of Lolium species resistant to acetolactate synthase‐inhibiting herbicide in and around grain‐importation ports in Japan

Compared with natural seed dispersal, human‐mediated seed dispersal could spread herbicide resistance genes on a much larger scale. Herbicide‐resistant weed seeds have been reported as contaminants in commercial grain. We investigated the contamination of seeds of Lolium species with target‐site mutations conferring resistance to acetolactate synthase (ALS)‐inhibiting herbicides in wheat imported from the USA, Canada and Australia into Japan. We also investigated the establishment of ALS‐inhibiting herbicide‐resistant Lolium species in 12 seaports in Japan that are major entry points for international commodities. We found herbicide‐resistant Lolium spp. seeds from all classes of wheat samples. Resistant individuals became established at six of eight ports where more than 50 kt of imported wheat is unloaded every year. The establishment of resistant Lolium spp. individuals was common at major grain landing ports. Monitoring over 3 years at one port revealed that the frequency of resistant individuals did not fluctuate between years. Many resistant individuals were distributed in front of the entrance of a fodder company, but a few resistant individuals were found in areas 2 km away from the port. The results indicate that gene flow is rare through pollen or seed movement from resistant plants to peripheral populations. Further extensive and long‐term monitoring is necessary to perform a comprehensive risk assessment of herbicide‐resistant plants entering Japan through major commercial ports.     

阿拉善—鄂尔多斯生物多样性中心的特有植物和植物区系的性质

阿拉善—鄂尔多斯是我国西北干旱区特有植物的集中分布区,有中国种子植物特有属１５个。其中,当地特有属５个、戈壁荒漠特有属２个、蒙古高原特有属１个。有当地种子植物特有种１２８个,其中贺兰山等山地特有种６２个、平原荒漠特有种６６个。该中心特有植物的性质,表现为古地中海旱生植物后裔的古老性和温带干旱荒漠性质,以及山地森林植物与华北或东亚植物的亲缘联系