Hybridizations and genetic relationships among Lindernia species (Scrophulariaceae): L. procumbens and two subspecies of L. dubia

Lindernia procumbens and L. dubia are common annual weeds in flooded rice fields of Japan. Two subspecies of L. dubia, subsp. major and subsp. dubia, are usually recognized in Japan but they are both regarded as synonyms of L. dubia elsewhere. In a cluster analysis based on AFLP, most L. dubia subsp. major formed a separate cluster from L. dubia subsp. dubia although 11% of haplotypes classified using AFLP were not coincident with classification using the shape of leaf bases, which is the commonly used identification trait. Artificial F₁ plants between L. procumbens and L. dubia subsp. major, and between L. procumbens and L. dubia subsp. dubia did not produce seed. Forty percent of capsules produced by F₁ plants from these two subspecies were slimmer and 80% pollen were sterile in slimmer capsules. However, seed number of most F₁ capsules was not different from that of self-fertilized plants, suggesting that there was no complete reproductive isolation between the subspecies. Natural hybridization of these subspecies may have occurred but we are not aware of it because F₁ plants are rare and F₂ plants are indistinguishable from these subspecies.     

外来入侵杂草传统生物防治的生态风险及其防范对策

长期大量实践说明,引进天敌防治外来入侵杂草的传统生物防治方法是治理外来入侵杂草的一条切实可行的有效途径,但对其潜在的生态风险——对本土生物的直接或间接不良影响不容忽视。利用传统评价方法预测候选天敌的生态风险存在缺陷,主要表现在：（1）寄主专一性测定过分依赖室内进行的生理寄主范围测定结果,对生态寄主范围（实际寄主范围）问题重视不够,后者指在新环境中的一系列物理和生物条件下的寄主利用预测;（2）在生理寄主范围测定中,过分依赖完成生长发育的可能性,对行为、遗传性状以及系统发育关系重视不够;（3）在风险评估中,过多强调对经济作物的风险,而对自然生态系统的风险重视不够。对此,建议：（1）鼓励对已释放的天敌进行回顾性跟踪研究,从而为杂草生物防治实践提供生态学理论支撑;（2）在运用生物防治手段对付外来入侵杂草实践中,建议采用“有害推论”的预防性原则,以避免在面临入侵生物重大威胁时草率做出释放天敌的决策;（3）在评估候选天敌风险中重视生态效应的风险评估。     

广聚萤叶甲成虫取食经历对后续 产卵寄主选择的影响

【背景】取食经历对植食性昆虫的寄主选择行为具有较大影响,影响天敌昆虫寄主专一性测定的设计和结果解释。【方法】采用选择性试验,观察了入侵豚草的重要天敌——广聚萤叶甲成虫羽化后取食不同植物对其后续产卵寄主选择的影响。【结果】与取食豚草的试虫相比,有取食三裂叶豚草、苍耳或菊芋经历的成虫选择苍耳产卵的频次增加,不再对豚草表现出明显的选择偏好性。对产卵识别期的Cox模型分析结果表明,成虫早期取食不同植物,对后续产卵选择有显著影响,成虫羽化后如果先取食豚草或三裂叶豚草,则选择苍耳产卵的倾向显著低于豚草;但如果先取食苍耳、菊芋和农家向日葵,则选择苍耳产卵的倾向与豚草无显著差异。【结论与意义】由此推测,广聚萤叶甲初羽化成虫取食的植物对其后续产卵选择具有较大影响,因而在寄主专一性测定中应关注测试前饲喂的植物种类。     

薇甘菊可溶性蛋白和抗氧化酶活性对田野菟丝子不同寄生密度的响应

为探求利用寄生植物田野菟丝予对入侵杂草薇甘菊进行生物控制的有效措施,研究了薇甘菊对0、1、2、4和8棵田野菟丝子幼苗寄生在可溶性蛋白和一些抗氧化酶活性方面的响应.寄生后30 d,1棵田野菟丝子/株薇甘菊（以下简称棵/株）以上的寄生密度导致薇甘菊可溶性蛋白含量显著降低.和对照相比,在寄生密度为1棵/株时,超氧物歧化酶(S...     

Dealing with scarce data to understand how environmental gradients and propagule pressure shape fine‐scale alien distribution patterns on coastal dunes

Questions: On sandy coastal habitats, factors related to substrate and to wind action vary along the sea–inland ecotone, forming a marked directional disturbance and stress gradient. Further, input of propagules of alien plant species associated to touristic exploitation and development is intense. This has contributed to establishment and spread of aliens in coastal systems. Records of alien species in databases of such heterogeneous landscapes remain scarce, posing a challenge for statistical modelling. We address this issue and attempt to shed light on the role of environmental stress/disturbance gradients and propagule pressure on invasibility of plant communities in these typical model systems. Location: Sandy coasts of Lazio (Central Italy). Methods: We proposed an innovative methodology to deal with low prevalence of alien occurrence in a data set and high cost of field‐based sampling by taking advantage, through predictive modelling, of the strong interrelation between vegetation and abiotic features in coastal dunes. We fitted generalized additive models to analyse (1) overall patterns of alien occurrence and spread and (2) specific patterns of the most common alien species recorded. Conclusion: Even in the presence of strong propagule pressure, variation in local abiotic conditions can explain differences in invasibility within a local environment, and intermediate levels of natural disturbance and stress offer the best conditions for spread of alien species. However, in our model system, propagule pressure is actually the main determinant of alien species occurrence and spread. We demonstrated that extending the information of environmental features measured in a subsample of vegetation plots through predictive modelling allows complex questions in invasion biology to be addressed without requiring disproportionate funding and sampling effort.     

Ranking buffel: Comparative risk and mitigation costs of key environmental and socio‐cultural threats in central Australia

Changed fire regimes and the introduction of rabbits, cats, foxes, and large exotic herbivores have driven widespread ecological catastrophe in Australian arid and semi‐arid zones, which encompass over two‐thirds of the continent. These threats have caused the highest global mammal extinction rates in the last 200 years, as well as significantly undermining social, economic, and cultural practices of Aboriginal peoples of this region. However, a new and potentially more serious threat is emerging. Buffel grass (Cenchrus ciliaris L.) is a globally significant invader now widespread across central Australia, but the threat this ecological transformer species poses to biodiversity, ecosystem function, and culture has received relatively little attention. Our analyses suggest threats from buffel grass in arid and semi‐arid areas of Australia are at least equivalent in magnitude to those posed by invasive animals and possibly higher, because unlike these more recognized threats, buffel has yet to occupy its potential distribution. Buffel infestation also increases the intensity and frequency of wildfires that affect biodiversity, cultural pursuits, and productivity. We compare the logistical and financial challenges of creating and maintaining areas free of buffel for the protection of biodiversity and cultural values, with the creation and maintenance of refuges from introduced mammals or from large‐scale fire in natural habitats. The scale and expense of projected buffel management costs highlight the urgent policy, research, and financing initiatives essential to safeguard threatened species, ecosystems, and cultural values of Aboriginal people in central Australia.     

特异性适应稻作系统的稗草种群生活史特性

长期进行除草剂药效试验可能会导致田间杂草种群发生适应性进化。本研究在安徽南陵县除草剂药效试验专用稻田中采集了1个稗草种群A,并以从常规稻田采集的3个稗草种群为对照,开展同质园栽培试验。结果表明: 与3个对照种群相比,A种群稗草植株的单株种子产量显著减少,种子千粒重显著增加,幼苗生长速率显著加快,结实分蘖数显著增多,生育期显著缩短;A种群稗草成株的株高、生物量及对除草剂五氟磺草胺的敏感性均显著降低。A种群稗草幼苗3～4叶期时经五氟磺草胺推荐剂量2倍量(有效成分60 g·hm^-2)处理后,其株高、生物量及成熟种子产量(平均每株1066粒)显著降低,而抽穗期、结实分蘖数、单个总状花序的种子数及种子千粒重无显著差异。因此,种子较重、生活史周期短、植株矮小、结实分蘖多及对除草剂五氟磺草胺具有抗药性,使得A种群稗草对稻作系统具有特异适应性,应防止此类种群扩散至常规稻田。     

珠三角地区四季草坪杂草群落组成及其生态位

利用倒置"W"九点取样法,对珠三角地区5个城市32个草坪样点进行了季节动态调查.结果表明:春季草坪杂草群落结构以水蜈蚣(KyUinga brevifolia)+三点金(Desmodium triflorum)+狗牙根(Cynodon dactylon)+积雪草(Asiatic pennywort)为主;夏季以水蜈蚣+三点金+香附子(Cypems rotundus)+伞房花耳草(Hedyotis corymbosa)为主;秋季以水蜈蚣+三点金+伞房花耳草+狗牙根为主;冬季以积雪草+水蜈蚣+天胡荽(Hydrocotyle sibthorpoioides)+三点金为主.运用改进的Levins生态位宽度指数和Pianka生态位重叠指数对四季优势杂草生态位进行分析,结果表明,大部分杂草生态位宽度在0.5以下,生态位宽度达到0.50的有水蜈蚣(四季均最高),三点金(秋季)、狗牙根(春季)、酢浆草(Oxalis pes-caprae)(春季).春季优势杂草的生态位重叠指数达到0.60的最多,冬季则最少.生态位重叠指数的最大值出现在夏季,分别是天胡荽和母草(Lindernia crustacea)、白花蛇舌草(Hedyotis diffusa)和瓶尔小草(Ophioglossum vulgatum)之间,可达0.85.     

Diffuse knapweed (Centaurea diffusa Lam.) seedling emergence and establishment in a Colorado grassland

Knapweeds (Centaurea spp.) are damaging invaders of grasslands and other North American rangelands. A field study was conducted to determine conditions that promote diffuse knapweed (C. diffusa) emergence and establishment in a native Colorado grassland (North America). Knapweed was planted in native grassland under treatments with different opening sizes, levels of competition, knapweed seed burial and season of seeding. There was no effect of opening size where competing natives were alive, but knapweed emergence in 5- and 15-cm openings was higher than 0-cm openings where natives were killed. Reducing competition reduced fall diffuse knapweed emergence, but did not affect spring emergence. Seed burial increased knapweed emergence, but the effect varied by season. Although diffuse knapweed emergence reached 35%, only four plants survived from 3,600 seeds. This native grassland did not prevent knapweed emergence or establishment, but both were so low that rapid knapweed invasion is unlikely.     

Role of invasive <Emphasis Type="Italic">Melilotus officinalis</Emphasis> in two native plant communities

This study examines the impact of the exotic nitrogen-fixing legume Melilotus officinalis (L.) Lam. on native and exotic species cover in two Great Plains ecosystems in Badlands National Park, South Dakota. Melilotus is still widely planted and its effects on native ecosystems are not well studied. Melilotus could have direct effects on native plants, such as through competition or facilitation. Alternatively, Melilotus may have indirect effects on natives, e.g., by favoring exotic species which in turn have a negative effect on native species. This study examined these interactions across a 4-year period in two contrasting vegetation types: Badlands sparse vegetation and western wheatgrass (Pascopyrum smithii) mixed-grass prairie. Structural equation models were used to analyze the pathways through which Melilotus, native species, and other exotic species interact over a series of 2-year time steps. Melilotus can affect native and exotic species both in the current year and in the years after its death (a lag effect). A lag effect is possible because the death of a Melilotus plant can leave an open, potentially nitrogen-enriched site on the landscape. The results showed that the relationship between Melilotus and native and exotic species varied depending on the habitat and the year. In Badlands sparse vegetation, there was a consistent, strong, and positive relationship between Melilotus cover and native and exotic species cover suggesting that Melilotus is acting as a nurse plant and facilitating the growth of other species. In contrast, in western wheatgrass prairie, Melilotus was acting as a weak competitor and had no consistent effect on other species. In both habitats, there was little evidence for a direct lag effect of Melilotus on other species. Together, these results suggest both facilitative and competitive roles for Melilotus, depending on the vegetation type it invades.