连续13年稻鸭共作兼秸秆还田的稻麦连作麦田杂草种子库物种多样性变化

稻鸭共作能有效控制稻田杂草的危害, 但是它对后茬小麦田杂草的影响及其控制作用尚没有详细的报道。我们于2000-2012年对江苏丹阳稻鸭共作兼秸秆还田的有机稻麦连作田土壤杂草种子库进行了连续13年的观察实验。结果显示, 稻鸭共作兼秸秆还田的措施使看麦娘(Alopecurus aequalis)、通泉草(Mazus japonicus)、碎米荠(Cardamine hirsuta)等18种麦田主要杂草的种子库均有较大幅度的降低, 总体的降低幅度高达97%。除了Pielou指数处于小幅波动状态外, 麦田杂草群落多样性指数整体呈下降趋势。丰富度下降表明杂草种子库向种类少、多样性低的方向演变。从Bray-Curtis指数和Jaccard相似性指数也可以得到同样的结论。可见, 连续稻鸭共作兼秸秆还田能够降低下茬的麦田土壤里杂草种子密度及多样性, 控制杂草危害。     

Weed seed bank response to tillage and residue management in semi-arid Zimbabwe

The influence of conservation agriculture (CA) on weed ecology has been a concern to many researchers across the world and is the focus of this study in southern Africa. An experiment to look at the impacts of various tillage systems with different levels of crop residue on maize (Zea mays L.) was established in 2004/2005 season. The experiment was carried out at the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), Matopos Research Station, Zimbabwe. Three main tillage systems were compared, ripping tillage (RT), planting basins (PB) and conventional tillage (CT), with three different crop residue levels: 0, 4 and 8 tons ha^?1. In 2007 soil samples were collected in the inter-row and in-row positions prior to tillage at 0–50 mm, 50–100 mm and 100–200 mm depths. The objective was to determine the effect of the treatment factors on weed seed bank species after three cropping cycles using the germination method. Nine major weed species were identified, with all the weeds unaffected by either tillage or mulching level. Eleusine indica, Corchorus tridens and Setaria species were the dominant weed species across all treatments. Setaria spp. was the dominant weed in the inter-row position of ripped plots. Although there was no significant individual treatment effect, there were significant (p < 0.05) interactions, with CT having reduced seed banks of Setaria spp. and E. indica compared to RT and PB. Percentage increases point to E. indica and Setaria spp. increasing under PB and RT compared to CT. C. tridens was significantly higher in PB compared to RT and CT in the 0–50 mm depth in the in-row position. This study probably coincided with the transition period in the weed bank succession process and needs to be repeated at a later date in the rotation. The majority of the weed species were not affected by any of the treatment combinations, a response attributed to plasticity of weeds to the tillage and residue level selection pressure.     

The biology of seed discrimination and its role in shaping the foraging ecology of carabids: A review

Species of carabid (ground) beetles are among the most important postdispersal weed seed predators in temperate arable lands. Field studies have shown that carabid beetles can remove upwards of 65%–90% of specific weed seeds shed in arable fields each year. Such data do not explain how and why carabid predators go after weed seeds, however. It remains to be proven that weed seed predation by carabids is a genuine ecological interaction driven by certain ecological factors or functional traits that determine interaction strength and power predation dynamics, bringing about therefore a natural regulation of weed populations. Along these lines, this review ties together the lines of evidence around weed seed predation by carabid predators. Chemoperception rather than vision seems to be the primary sensory mechanism guiding seed detection and seed selection decisions in carabid weed seed predators. Selection of weed seeds by carabid seed predators appears directed rather than random. Yet, the nature of the chemical cues mediating detection of different seed species and identification of the suitable seed type among them remains unknown. Selection of certain types of weed seeds cannot be predicted based on seed chemistry per se in all cases, however. Rather, seed selection decisions are ruled by sophisticated behavioral mechanisms comprising the assessment of both chemical and physical characteristics of the seed. The ultimate selection of certain weed seed types is determined by how the chemical and physical properties of the seed match with the functional traits of the predator in terms of seed handling ability. Seed density, in addition to chemical and physical seed traits, is also an important factor that is likely to shape seed selection decisions in carabid weed seed predators. Carabid responses to seed density are rather complex as they are influenced not only by seed numbers but also by trait‐based suitability ranks of the different seed types available in the environment.     

Soil seedbank: Old methods for new challenges in agroecology?

The weed soil seedbank is of interest in agroecosystems as a major source of weed infestation in fields and as a reservoir of plant and seed‐feeder diversity. A seedbank is a characteristic of annual plants and has been the focus of numerous studies, as it reflects the past aboveground vegetation and is the reservoir of the future vegetation. Therefore, it potentially can be used to evaluate the past, present and future annual weed communities. The goal of this paper was to provide guidelines to help researchers to do a weed seedbank survey. Through a qualitative review of 60 weed seedbank articles, we investigate why and how the seedbank has been studied in agronomy. It shows that seedbank studies have been performed to address the following four major objectives: (a) the assessment of weed management practices on weed communities; (b) the relationship between seedbank and aboveground vegetation; (c) the study of composition and diversity of seedbank in a given area; and, (d) the quantification of seedbank as a food resource for wildlife. Because the analysis highlighted a wide range of methodologies to estimate the seedbank, we critically reviewed them. We show that the selected methodology strongly affects the seedbank estimate. Nevertheless, in our sample of research articles, the analysis revealed that the choice of the methodology was not always justified in terms of achieving a particular scientific goal, but was often determined by the resources available for the experiment (e.g., workload). While studying the soil seedbank remains of interest for scientists (proved by the amount of recent publications), it is time consuming and requires considerable botanical skill. Innovative methods of estimation are scarce and novel methodological developments are needed to increase the quality and reliability of the data obtained.     

Interspecific variation in persistence of buried weed seeds follows trade‐offs among physiological,chemical, and physical seed defenses

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进境美国高粱截获杂草种子现状分析

【目的】近年来,美国高粱开始大量进入我国,其携带的杂草种子状况尚未有相关研究。通过对进境美国高粱携带的杂草种子现状进行分析,可为出入境检验检疫机构的检疫监管和后续监测提供依据。【方法】通过对2014—2016年进境美国高粱截获的杂草种子的研究,了解其携带的杂草种子状况。【结果】黄埔检验检疫局和南沙检验检疫局从进境的美国高粱中截获的杂草种子种类共涉及19个科106种。主要包括禾本科27种、菊科14种、大戟科3种、茄科2种、苋科15种、豆科10种、蓼科7种、锦葵科4种、旋花科7种、十字花科4种、藜科4种等,其中检疫性杂草共涉及5科25种,检出率高。【结论】美国高粱携带的杂草种子数量大,种类丰富,检疫性杂草含量大,应予以高度重视。     

Comparison of Sex Pheromonal Activity on the American Cockroach between Acetates and Propionates of Verbenyl Type Alcohols

Sex pheromonal activity was evaluated for propionates of 4 alcohols having a 6,6-dimethyl-bicyclo[3.1.1]heptane skeleton by behavioral assay with the male American cockroach. Their activities were compared with the corresponding acetates. The propionates were active at 20 μg or 500 μg, demonstrating stronger activities than the corresponding acetates. The male to female response ratio (M/F ratio) in EAG was also evaluated for the acetates and propionates, as well as for germacrene-D and camphor. The order of the behavioral activity was represented by that of the ratio. Sex pheromonal activity of (+)-verbanyl propionate (7) and germacrene-D were compared. Stronger activity was consequently observed in 7 at 5 μg dose, supporting the M/F ratio result.     

杂草种子传播研究进展

种子传播将母株生殖周期的末端与它们后代种群的建立连结了起来,广泛认为,其对植被结构具有深刻的影响。种子传播的整个过程称为种子传播循环。研究表明,杂草种子传播的因子多种多样,包括仅依赖自身来完成的主动传播,以及依赖风、水、动物、人类等外界媒介的被动传播。其中,人类传播杂草种子是影响最广泛的一种,对现代植物的分布格局产生了深刻的影响。杂草种子的传播,对杂草种子库的数量和空间动态影响很大。研究种子传播的主要方法有荧光染料标记法、放射性同位素标记法、稳定同位素分析、分子遗传标记等。结合近几年国内外的研究进展,作者就杂草种子传播对种子库数量和空间动态影响的精确直接研究、杂草种子传播的过程及传播后的命运、杂草种子适应传播的机理、生态控草措施研究、外来杂草入侵蔓延与其种子传播的关系等方面提出了展望。     

Soil water potential and temperature sum during reproductive growth control seed dormancy in Alopecurus myosuroides Huds.

The sustainable management of unwanted vegetation in agricultural fields through integrated weed control strategies requires detailed knowledge about the maternal formation of primary seed dormancy, to support the prediction of seedling emergence dynamics. This knowledge is decisive for the timing of crop sowing and nonchemical weed control measures. Studies in controlled environments have already demonstrated that thermal conditions and, to some extent, water availability during seed set and maturation has an impact on the level of dormancy. However, it is still unclear if this applies also under field conditions, where environmental stressors and their timing are more variable. We address this question for Alopecurus myosuroides in south‐western Sweden. We quantified the effects of cumulated temperature and precipitation as well as soil water potential during the reproductive growth phase of A myosuroides on primary seed dormancy under field conditions. Empirical models differing in focal time intervals and, in case of soil water potential, focal soil depths were compared regarding their predictive power. The highest predictive power for the level of primary dormancy of A. myosuroides seeds was found for a two‐factorial linear model containing air temperature sum between 0 and 7 days before peak seed shedding as well as the number of days with soil water potential below field capacity between 7 and 35 days before peak seed shedding. For soil water potential, it was found that only the top 10 cm soil layer is of relevance, which is in line with the shallow root architecture of A. myosuroides. We conclude that for this species the level of dormancy depends on the magnitude and timing of temperature and water availability during the reproductive growth phase. Water availability appears to be more important during maternal environmental perception and temperature during zygotic environmental perception.     

Utilization of an unpredictable food source by Melanterius ventralis, a seed-feeding biological control agent of Acacia longifolia in South Africa

A seed-feeding weevil, Melanterius ventralis (Coleoptera: Curculionidae), has been introduced into South Africa to supplement a gall wasp,Trichilogaster acaciaelongifoliae (Hymenoptera: Pteromalidae), in the biological control programme against an alien invasive tree, Acacia longifolia (Mimosaceae), from Australia. The gall wasp debilitates most of the flower buds on A. longifolia andreduces seed-set by >95%. The intended rolefor M. ventralis is to destroy theresidual seeds. To achieve this, the gravidfemales need to be able to locate a food sourcethat is both heterogeneously dispersed andfrequently scarce due to damage caused by T.acaciaelongifoliae. Observations showedthat M. ventralis females are meticulousin choosing sites to oviposit so that larvae donot become overcrowded and food limited. Cagetests and field observations revealed thatfemales located pods regardless of density andposition, and that the duration of time spenton branches was proportional to the number ofpods on the branches and to the condition ofpods. The females spent little time onbranches of acacia species other than A.longifolia, but some time was spent onbranches with pods of A. melanoxylon thathad been coated with juice extracted from A.longifolia. All indications are that M.ventralis has the attributes needed to bean excellent supplementary biological controlagent to T. acaciaelongifoliae and theprogress of the weevil continues to be monitored.     

The potential of seed‐eating birds to spread viable seeds of weeds and other undesirable plants

The potential for seed‐eating birds to spread viable seeds was investigated using captive‐feeding trials to determine seed preference, passage time through the gut, and viability of passed seeds for bronzewing pigeons (Phaps chalcoptera), peaceful doves (Geopelia striata), crested pigeons (Ocyphaps lophotes), Senegal doves (Streptopelia senegalensis), zebra finches (Taeniopygia guttata), black ducks (Anas superciliosa) and wood ducks (Chenonetta jubata). Test seeds were bladder clover (Trifolium spumosum), crimson clover (Trifolium incarnatum), gorse (Ulex europaeus), canola (Brassica napus) and red panicum (Setaria italica). Their consumption was compared with that of commercial seed mixes. Although all test seeds were recognizable foods, their consumption usually decreased in the presence of other foods, except for canola, where consumption rates were maintained. Hard‐seeded bladder clover was the only species where viable seeds were passed by obligate seedeaters. In contrast, viable seeds of canola and gorse were passed by seed‐eating omnivorous/herbivorous ducks, although the germination of passed seeds (42%) was reduced significantly compared with that of untreated control seed (67%). Field validation with wild, urban bronzewings and Australian magpies (Gymnorhina tibicen) offered canola and commercial seed yielded similar outcomes, with a range of viable seeds recovered from magpie soft pellets. Mean seed passage time in captive birds ranged from 0.5 to 4.3 h for all test seeds and commercial seed mixes, suggesting that these bird species may potentially disperse seed over moderate distances. Despite the low probability of individual birds spreading viable seed, the high number of birds feeding in the wild suggests that the potential for granivorous and seed‐eating omnivorous birds to disperse viable seeds cannot be discounted, particularly if exozoochorous dispersal is also considered.     

Soil steaming effects on weed seedling emergence under the influence of soil type,soil moisture,soil structure and heat duration

Soil steaming applied in bands is a new technology with the potential to radically lower the burden of hand‐weeding intra‐row weeds in non‐herbicidal vegetable cropping. Preliminary studies with band‐steaming have shown effective control of viable weed seeds when the maximum soil temperatures reach 60–80°C. This temperature range has a particular agronomic interest, and the present study aimed at investigating the influence of soil factors and heat duration on weed seed mortality of soil steaming targeting 60–80°C. Two soil types (sand versus sandy loam) and two moisture levels (moist versus dry) were studied in one experiment (expt) while two levels of structure of a sandy loam (coarse versus fine) were included in a second experiment. A third experiment was focussing on the significance of heat duration expressed as the speed of cooling‐down after steaming had been stopped. Weed control efficacy was generally greater in sand than in sandy loam and soil irrigation further improved weed control. Steam application to the finely structured soil improved weed control efficacy relative to that obtained with the coarse soil of larger aggregate size. The rapidity of cooling from the maximum temperature did not affect the efficacy of the treatment on weed seed mortality. Based on these experiments, a maximum soil temperature of 80°C should ensure satisfactory weed control under moist soil conditions, especially if the soil is cultivated prior to steaming.     

Ecological characteristics of Brachychiton populneus (Sterculiaceae) (kurrajong) in relation to the invasion of urban bushland in south‐western Australia

Brachychiton populneus (Sterculiaceae) (Schott et Endl.) R. Br. (kurrajong) is a small tree that occurs naturally ranging from southern Queensland to Victoria. It has been widely planted as an ornamental tree in south‐western Australia. In Kings Park, B. populneus has moved from cultivation to become a weed in the adjoining bushland reserve. The aim of this study was to examine the ecology of B. populneus and the Kings Park environment in order to identify the particular conjunction of characteristics that have led to the species becoming a weed. The highest density of kurrajongs (69.3 trees ha^–1) was observed in the most disturbed area of Kings Park, and there was a strong relationship between density of B. populneus and disturbance (P = 0.058). The most striking feature of the invasion was the tendency of B. populneus to occur beneath other tree species, and this was attributed to birds feeding on transported fruit in trees and rats building seed caches at their base. Mature trees produced large amounts of viable seed, but rates of seed predation were high. Weevils, beetle larvae and omnivorous vertebrates such as Australian ravens, magpies and introduced black rats were observed eating seeds. The foraging behaviour of the vertebrates may facilitate the dispersal of seeds for relatively long distances away from parent plants. Seeds that escape predation form a transient seed bank and germinate with the onset of the winter rains. Early in their development, seedlings allocate resources to form a large tap‐rooted tuber that has substantial starch and water reserves, allowing seedlings to survive the long dry and hot summers in Perth. The study observed that B. populneus could survive at least one fire by resprouting from basal dormant buds. Brachychiton populneus appears to have become a weed in Kings Park because, first, it is dispersed widely into new sites through the foraging behaviour of vertebrates and once germinated has no grazing pressure, and, second, its development of a root tuber and ability to resprout means the seedlings are resilient in this frequently disturbed Mediterranean environment. While management of existing plants is relatively straightforward, continued vigilance will be required to avoid reinvasion.     

Effects of brassinosteroids on conditioning and germination of clover broomrape (Orobanche minor) seeds

Brassinolide [2, 3, 22R,23R-tetrahydroxy-24S-methyl-B-homo-7-oxa-5--cholestan-6-one] and its related compounds, brassinosteroids, applied at the early stages of conditioning shortened the conditioning period required before clover broomrape seeds would germinate after exposure to germination stimulants, such as dl-strigol and natural stimulants from red clover (Trifolium pratense L.) root exudate. Brassinosteroids applied after conditioning increased the rate of the seed germination induced by these stimulants. The inhibitory effect of light on seed germination when it was induced by dl-strigol could be overcome by brassinosteroids. Brassinosteroids also eliminated the inhibitory effects of light and dl-strigol applied at the early stages of conditioning. GA₃ was also effective in causing seed conditioning and increased the rate of the germination induced by these stimulants. There was a relationship between brassinosteroids and GA₃ in many of the experiments conducted. These findings may have practical implications in increasing the effectiveness of applying germination stimulants in the field to soils for suicidal germination of broomrape seeds.     

The effect of temperature on viability of imbibed weed seeds

Imbibed seed of 10 common arable weeds were placed in trays in initially moist soil and, after imbibing for 2h, heated in ovens/incubators set to 31^oC, 42^oC, 56^oC, 75^oC or 100^oC for 0.5, 1, 2, 4, 8 or 16 days or at 102^oC, 155^oC, 204^oC or 262^oC for 0.5, 1, 2, 5, 7.5 or 10 min. After heating, seeds were incubated for 28 days at 10/20^oC or 20/30^oC on a 12 h dark/light regime, depending on species, and germination recorded. At the lower temperatures, germination of all species was prevented by temperatures of 75^oC or higher for periods of 0.5 days or more. Germination was lower after treatment at 56^oC than at 31^oC or 42^oC for all species except Rumex obtusifolius. The maximum temperature required to prevent germination varied among species and was of greater importance than the duration of heating. Germination was variable with duration of heating. At the higher temperatures, there was very little germination of any species after heating at 204^oC for 7.5 min or 262^oC for 5 min or more. Seeds were greatly buffered from the air temperature by 3 mm of soil, throughout the shorter duration of heating. The average temperature of the soil, over the 10 min heating required to prevent over 90% germination, varied among species and ranged from 48^oC for Avena fatua to 65^oC for R. obtusifolius. This work implies that composting systems maintained at 65^oC are unlikely to provide an efficient method of weed control. Recommendations for improvement of the laboratory technique are suggested.