A study of the population dynamics of Avena fatua L. as influenced by straw burning, seed shedding and cultivations

An infestation of Avena fatua in two successive spring barley crops was monitored from March 1972 to June 1973. The numbers of viable seeds on the uncultivated stubble, viable seeds in the soil, and seedlings emerging in autumn and spring were assessed. Both seed and seedling populations declined when seeding was prevented in 1972, hut increased in all situations where seeding occurred. The greatest increase occurred when the unburnt stubble was cultivated after harvest; the increase was less following straw burning. The greatest losses of newly shed seeds occurred when the stubbles were left uncultivated throughout the autumn, and delaying cultivation was more effective than burning in limiting the rate of increase. Old seeds, already in the soil before 1972, were less dormant and produced a higher percentage of seedlings in 1973 than did seeds shed in 1972. Once in the soil, the greatest losses of seeds occurred during the spring, and it is likely that many seeds germinated but failed to establish as seedlings. It is suggested that the seed reserves of A. fatua in the soil are less persistent than previously reported, especially where mouldboard ploughing is replaced by tine cultivation. The periodicity of seedling emergence in spring was unaffected by the time or type of cultivation, by the age of the seeds or by burning the straw in the previous autumn. Etude de la dynamique d'une population d'Avena fatua soumise à l'influence du brûdage de la paille, de la chute des semences et des façons culturales. Une infestation d'Avena fatua, dans deux cultures successives d'orge, a été observée depuis mars 1972 jusquà juin 1973. Les nombres des semences viables dans le chaume non cultivé, des semences viables dans le sol, et des plantules levant à l'automne et au printemps, ont étéévalués. Les populations de semences et de plantules ont toutes deux diminué lorsque la montre à graine a été empêchée en 1972, mais se sont accrues dans toutes les situations ou la mise k graines s'est produite. L'aceroissement le plus important s'est produit lorsque les chaumes non brûlés ont été cultives apres la moisson; l'aceroissement a été plus faible apres le brülage de la paille. Les pertes les plus élevées de semences récemment tombées se sont produites lorsque les chaumes sont restes non cultives durant tout rautomne, et le retard des fagons culturales a été plus efficace que le brülage pour limiter le taux d'aecroissement. Les semences anciennes, qui étaient dans le sol avant 1972, ont été moins dormantes et ont produit, en 1973, un pourcentage plus élevé de plantules que les semences tombées en 1972. Une fois dans le sol, les plus grandes pertes de semences se sont produites pendant le printemps et il est vraisemblable que de nombreuses semences ont germé mais n'ont pas abouti a l'établissement de plantules. II est suggéré que les réserves de semences d'Avena fatua dans le sol sont moins persistantes qu'on ne le pensait autrefois, particulierement lorsque le labour avec une charrue à versoir est remplacé par un travail avec des appareils á dents. La périodicité des leviés au printemps n'a pas été affectée par I'époque ou par le type de façon culturale, ni par l'âge des semences ou par le brülage de la paille à Tautomne précédent. Eine Untersuchung iiber die Populationsdynamik von Avena fatua L unter dem Einfluss von Strohabbrennen, Samenfall und Bodenbearbeitung In einer Folge von Sommergerste auf Sommergerste wurde der Flughaferbefall von Mai 1972 bis Juni 1973 beobachtet. Die Anzahi lebensfähiger Samen (Karyopsen) in der unbear-beiteten Stoppel und im Boden wie auch die Anzahl der im Herbst und Frühjahr aufgelaufenen Keimpflanzen wurde erfasst. Sowohl die Samenwie auch die Keimpflanzenpopula-tion ging 1972 zurück nachdem das Aussamen verhindert wurde, nahm aher in jedem Fall wieder zu, wenn die Pflanzen aussamen konnten. Die siärkste Zunahme trat dann ein, wenn die nicht abgebrannte Stoppel nach der Emte bear-beitet wurde; nach Stoppelabbrennen war sie geringer. Die grössle Ahnahme frisch ausgefaltener Samen trat dann ein, wenn man die Stoppel den ganzen Herbst unbearbeiter liess und eine spate Bodenbearbeitung war im Hinblick auf die Zunahme an Flughafer wirkungsvoller als das Abbrennen. Alte Samen, die berelts vor 1972 im Bodden waren. zeigten eine geringere Keimhemmung und produzierten 1973 mehr Keimpflanzen als Samen die erst 1972 ausfielen. Die grossten Verluste an den im Boden vorhandenen Samen trat im Fruhjahr auf und wahrscheinlich konnten viele gekeimten Samen als Keimpflanzen nicht ijberteben. Man kann anneh-men. dass der Samenvorrat von A. fatua im Boden kurzlebiger ist als fruher angenommen wurde, besonders dort, wo Pfliigen durch Grubbern ersetzt wurde. Die Regelmassigkeit des Flughaferauflaufs im Friihjahr war unbeeinflusst vom Zeitpunkt und Art der Bodenbearbeitung, vom Alter der Samen oder vom Abbrennen des Strohs im vorausgegan-gcnen Herhst.     

Breeding systems and seed production for six weedy taxa of Bidens

Successful reproduction is considered to be the major determining factor for a weedy population to establish, colonize and infest. The breeding systems and seed production of six weedy taxa of Bidens were studied at an experimental garden in Jiangsu province in China. The results from four treatments (open pollination, bagged capitulum, decapitated capitulum, and pollen supplement) indicated that, with the exception of Bidens pilosa var. radiata, all the other five Bidens taxa; namely, B. pilosa var. pilosa, B. pilosa var. minor, B. frondosa, B.bipinnata, and B. biternata, were self‐fertile with a high seed‐set in bagged capitula, and a high autofertility index. Including the trait of vegetative propagation in self‐incompatible B. pilosa var. radiata, all the six weedy taxa of Bidens had the capacity of uniparental reproduction. The pollen limitation values for all six Bidens taxa were low in the present study. However, the seed production of B. pilosa var. radiata is likely to decrease in the absence of sufficient pollinators, related to its high pollen contribution and potential pollen limitation indices. The seed production per plant and per capitulum of the three varieties of B. pilosa was the highest among the six taxa and might contribute to their serious weediness. The breeding system type and seed number per capitulum could be used as a classification reference for Bidens taxa.     

The influence of crop rotation and soil tillage on seed population dynamics of A vena sterilis ssp. ludoviciana

The dynamics of seed populations of Avena sterilis ssp. ludoviciana (Durieu) Nyman in plots maintained under different crop rotations and tillage systems was studied over a 5-year period. The seed reserves buried in the soil were practically depleted during this period by using any of the three cropping systems evaluated. No significant differences were found between using a continuous barley rotation with annual application of herbicides and using a barley:fallow rotation with herbicides applied only as needed. The decline in seed populations was not affected by the tiliage system used during the fallow period (ploughing or no tillage). The tillage practices used in the various treatments, combined with the variable seed output from each treatment, resulted in different vertical distribution of the seeds in the soil profile. Shallow cultivation resulted in an accumulation of seeds in the upper soil layers; in contrast, a large proportion of the seeds were buried and maintained below 15 cm in the ploughed treatments. Although the seed distribution patterns produced by the various tillage systems had an effect on seedling recruitment, the largest changes in this parameter were associated with the different cropping sequences. Four times more seedlings were recruited in years under barley cropping than in those under fallow.     

Population dynamics of Eupatorium adenophorum Spreng. and Eupatorium riparium Regel in relation to burning

The population dynamics of Eupatorium adenophorum Spreng. and E. riparium Regel was studied in the field for 2 years, in relation to burning, by following the fate of individuals in permanent quadrats at short and regular time intervals. Both species showed increased population density and longevity of individuals on the burnt site. Adult and seedling populations of both species showed greater survival in the burnt plot. Eupatorium riparium survived better than E. adenophorum adults after burning. In the unburnt plot, however, the seedling survival of both species was nil. The heavy juvenile mortality of both species in the unburnt situation is attributed to the accumulation of a thick layer of pine needles and the growth of herbaceous vegetation. Moisture stress and low temperature in winter months also seem involved in the regulation of seedling population of these two weeds.     

UV-absorbing compounds and susceptibility of weedy species to UV-B radiation

Stratospheric ozone (O₃) depletion has led to increased terrestrial ultraviolet‐B (UV‐B) radiation (290–320 nm). Leaves exposed to this radiation produce UV‐absorbing compounds in the epidermal cells, which protect plants from UV‐B damage. To determine the role of UV‐absorbing compounds in the UV‐B sensitivity of weeds (common chickweed (Stellaria media), downy brome (Bromus tectorum), green smartweed (Polygonum scabrum), redroot pigweed (Amaranthus retroflexus), spotted cat’s‐ear (Hypochoeris radicata), and stork’s‐bill (Erodium cicutarium)) seedlings were exposed to 0, 4 (field ambient), 7 (18% O₃ depletion) and 11 (37% O₃ depletion) kJ m^?2 d^?1 of biologically effective UV‐B radiation in a greenhouse. Ultraviolet‐absorbing compounds were extracted from the second true‐leaf (0.5 cm² samples) with methanol : distilled water : HCl (79 : 20 : 1) in an 85°C water bath for 15 min, and the absorbance of the extracts measured at 300 nm. The shoot dry biomass was recorded to determine the susceptibility to UV‐B radiation. Common chickweed was the most sensitive and green smartweed the least sensitive weed to UV‐B radiation. The latter accumulated more UV‐absorbing compounds and this accumulation occurred earlier compared with common chickweed. As UV‐B_BE radiation levels increased from 0 to 11 kJ m^?2 d^?1, the green smartweed shoot biomass did not decline. However, the biomass of all five susceptible species declined despite an increase in the UV‐absorbing compounds in response to increased UV‐B radiation. Therefore, formation of a ‘UV‐screen’ in these species is not sufficient to fully prevent UV‐B damage. When the concentration of UV‐absorbing compounds in the six species was plotted against their susceptibility to UV‐B radiation, no relationship was observed. Thus, while the accumulation of UV‐absorbing compounds may be a major factor in the protection of certain species against UV‐B radiation and may offer some degree of defence in other species, it does not explain UV‐B susceptibility differences in weedy species in general.     

基于3种原噬菌体基因的赣南地区黄龙病菌种群动态分析

柑橘黄龙病(citrus Huanglongbing,HLB)对全球柑橘产业造成了重大经济损失。为明确赣南地区柑橘黄龙病菌基因组上原噬菌体的分子特征和传播动态,本研究对采自赣南10个市县区的470份样品进行HLB检测,并对阳性样品中3种类型的原噬菌体（SC1、SC2和P-JXGC-3）上的SC1_gp050、SC2_gp040和PJXGC_gp08基因序列进行遗传多样性分析和谱系地理学分析。结果显示,共检出74份HLB阳性样品,包括7种原噬菌体组合类型:SC1、SC2、P-JXGC-3、SC1+SC2、SC1+P-JXGC-3、SC2+P-JXGC-3和SC1+SC2+P-JXGC-3,含SC2类型的原噬菌体检出41份,检出率为55.41%,说明赣南地区含SC2类型的原噬菌体菌株最为普遍。遗传多样性分析结果表明,赣南地区的3种原噬菌体的基因交流频繁,遗传分化现象不明显。选择压力分析结果显示,SC1和P-JXGC-3类型的原噬菌体均处于负向选择,SC2类型的原噬菌体处于正向选择。基于3种原噬菌体上的基因构建的中介网络图和单倍型分布表结果显示,3种原噬菌体均存在1个祖先单倍型,其他独有单倍型均是由该祖先单倍型经多次突变而来,其中PJXGC_gp08基因产生的独有单倍型最多。时空动态分析结果显示,SC1类型原噬菌体存在2条传播路径,分别为安远和全南地区间的相互传播(3相似文献   

广西旱地作物主要金龟子种类及其发生动态初步调查

2011-2013年, 通过挖土调查和太阳能诱虫灯系统调查了广西各地旱地作物金龟子的种类及其种群动态。统计结果表明, 全区共采集到金龟子4个科56种, 发生盛期为4月底至7月上旬; 各地发生种类和时期不同, 主要优势种为深绿异丽金龟、红脚异丽金龟、异丽金龟和桐黑异丽金龟, 发生盛期分别为5月下旬至7月中旬、6月中旬至8月上旬、5月中旬至6月中旬、5月中旬至6月下旬。     

Electrophoretic study of three related Phytophthora species1

Morphological and cultural characters currently used for the classification of species of Phytophthora are inadequate to distinguish P. cryptogea, P. drechsleri and P. erythroseptica. In this study isolates of the above-mentioned species, including type and/or authentic cultures of P. cryptogea and P. drechsleri were compared. Morphological and cultural characters, together with electrophoretic patterns of both total mycelial proteins and isozymes (arylesterase and malate dehydrogenase), allowed the distinction of P. erythroseptica from the others. Authentic cultures of P. cryptogea and P. drechsleri showed distinctly different electrophoretic patterns of arylesterase and malate dehydrogenase isozymes and of total mycelial proteins. Some Italian isolates previously identified as P. cryptogea or P. drechsleri showed features of both species, therefore it was impossible to discriminate the two species solely on the basis of the electrophoretic patterns of mycelial proteins.     

Uprooting and shearing resistances in the seedlings of four weedy species

For mechanical weeding, the uprooting force of whole seedlings and the shearing force of basal stems were measured in two grass weeds ( Setaria faberi and Echinochloa crus-galli var. crus-galli ) and two broad-leaved weeds ( Chenopodium album and Amaranthus patulus ), using balance-type equipment and a pair of scissors, respectively. Seedlings were grown in plastic pots. Uprooting and shearing experiments were carried out on the 11th, 16th, 21st, and 26th days after sowing. The uprooting force, the shearing force required to fracture the specimen, plant dry matter weight and cross-sectional area exponentially increased as seedlings grew, but the uprooting stress and shearing toughness maintained similar values after the 2nd sampling time, except for the 3rd and 4th sampling times in C. album . The increases in uprooting force and the shearing force required to fracture the specimen were supported by an expansion of the cross-sectional area of stems of the broad-leaved weeds or pseudostems of grass weeds. The higher values of uprooting stress and shearing toughness in C. album were related to an increased area of lignified organs in the basal stems. There was a significant correlation between uprooting and shearing forces. The shearing force was always higher than the uprooting force, so that most seedlings were uprooted and not fractured at the basal stems or pseudostems. The mean ratio of uprooting force to root dry matter weight after the 2nd sampling time suggested a high uprooting resistance at an extremely low amount of root dry matter weight.     

麦长管蚜自然种群结构动态的初步研究

采用田间系统调查的方法,观察了麦长管蚜在小麦拔节期一成熟期种群结构的动态.结果显示,麦长管蚜在种群发展过程中世代重叠,内部组成结构是一个有翅型与无翅型、成虫与若虫并存的混合体;各组分占种群的比例不均等.并随着小麦生育期和麦蚜种群发展过程而变化.在小麦乳熟期,翅型和虫态结构的比例表现为有翅型高于无翅型.若虫低于成虫.在其他生育期,则有翅型低于无翅型,低龄若虫>成虫>高龄若虫.结果表明,麦长管蚜内部结构的比例动态与小麦生育期关系密切,其组成结构特征直接反映了麦长管蚜种群的兴衰.     

漯河地区灯下夜蛾种类及种群发生动态

2015年4—10月,在河南省漯河市农业科学院试验基地设置自动虫情测报灯,系统诱集夜蛾科昆虫并鉴定种类、数量和优势种,分析夜蛾种群和优势种的发生动态。结果表明,夜蛾科昆虫年诱集量23 478头,分别隶属于44种,发生盛期为7月下旬到8月中、上旬;甜菜夜蛾、二点委夜蛾和黏虫是优势种,前两者发生盛期分别在8月中、上旬和7月中、下旬,黏虫的发生盛期在5月下旬到6月中旬和7月中、下旬;迁飞性害虫是漯河地区灯下夜蛾昆虫的主要类群。     

紫茎泽兰的生态学研究概况

紫茎泽兰是一种生长迅速、繁殖率高、能排挤本土物种形成单优群落的外来物种,同时能使入侵地的生物多样性丧失、严重破坏当地的生态系统.通过对紫茎泽兰生长的生物学特性、营养、环境、需光特性以及紫茎泽兰的种子库和化感作用等的阐述,旨在为同行学者对紫茎泽兰的进一步研究提供可借鉴的依据.     

江苏省扬中杂草稻生物学特性初步研究

扬中杂草稻具备杂草稻的基本特性，又是一个具有遗传多样性的混合群体。扬中杂草稻具有较强的休眠性，但比稽稻等代表性的杂草稻弱。扬中杂草稻落粒性强，与稽稻等代表性杂草稻表现基本一致。亲和性研究表明，扬中杂草稻与广亲和品种02428（S5^n）正反交杂种F1结实率正常，而与籼稻特青和扬稻6号的杂种F1生育期超亲，在南京不能正常抽穗。与粳稻武运粳7号、粳稻品系27114的杂种F1表现为半不育。     

锦鸡儿种子劣变过程中生理生化特性的研究

采用人工老化方法,在高温高湿(40℃、RH100%)条件下,对小叶锦鸡儿(Caragana microphlla Lam.)和柠条锦鸡儿(Caragana korshinskii Kom.)的种子进行劣变处理.同时重点测定和分析生理生化指标.结果表明:高温高湿(40℃,100%RH)人工老化法的最佳处理时间梯度为0、8、16、24、36、48 h.两种供试种子发芽率和发芽指数显著下降(P＜0.05);酸性磷酸酯酶活性显著降低(P＜0.05),与种子发芽指教呈极显著正相关,是反映其种子质量的敏感指标;可溶性糖泄漏和脂质过氧化,是种子劣变的重要原因.     

Seed survival and periodicity of seedling emergence in four weedy species of Papaver

Seeds of Papaver argernone, P. dubium, P. lecoqii and P. rhoeas were collected in each of three or four years and mixed with the top 7·5 cm of sterilized soil confined in cylinders sunk in the ground outdoors and cultivated three times yearly. Except for P. argemone, no more than 6% of seeds produced seedlings in the autumn of sowing; seedling numbers were usually greatest in the following year and then decreased exponentially from year to year. Mean survival of viable seeds after 5 years ranged from 7·4% for P. lecoqii to 2·0% for P. argemone. Most seedlings of all four species emerged in early spring and early autumn; emergence of P. rhoeas was greater in spring than in autumn, but the reverse was true for the other three species.     

Effects of dose and application timing on the seed production of three weed species treated with MCPA or tribenuron-methyl

The seed production of Fallopia convolvulus (L.) A. Love, Galium spurium L, and Thlaspi arvense L., treated with MCPA or tribenuron-methyl, was studied in a pot experiment. The herbicides were applied in doses from 1/16 to 1/l of a full dose at five different growth stages. The largest reduction of seed production was observed on plants treated when one true leaf had developed (F. convolvulus, both herbicides) or at the beginning of the generative phase (G. spurium treated with tribenuron-methyl and T. arvense treated with either herbicide). Tribenuron-methyl (0.375 g a.i. ha^?1) or MCPA (0.1875 kg a.i. ha^?1) applied at bolting stage was enough to reduce the seed production of T. arvense by 83% and 100%, respectively. The seed production of F. convolvulus, treated with 0.75 kg MCPA at the cotyledon stage, was reduced by 70%. Plants of G. spurium with 5–9 axillary shoots, treated with 3 g tribenuron-methyl, produced 45% fewer seeds than the control. Both herbicides (at least at the highest doses) reduced seed production of all three species more than shoot dry matter.     

3种蚜虫对方斑瓢虫适合度及种群增长的影响

方斑瓢虫是新疆农田常见的天敌昆虫之一,具有重要的控害潜能和应用前景。本文利用生命表技术探讨了棉蚜、桃蚜和豌豆修尾蚜对方斑瓢虫生长发育、存活率、繁殖力、寿命和种群数量增长趋势的影响。结果表明,与饲喂豌豆修尾蚜的方斑瓢虫种群相比,饲喂棉蚜和桃蚜的种群幼虫发育历期和平均世代周期更短,存活率、雌虫产卵量、卵孵化率、成虫寿命、内禀增长率、周限增长率和种群趋势指数更高。饲喂棉蚜、桃蚜和豌豆修尾蚜的方斑瓢虫幼虫存活率分别为85.83%、88.33%和50.83%,单雌产卵量分别为516.71、439.95粒和209.00粒,以棉蚜和桃蚜为食的幼虫存活率和雌虫产卵量均显著高于以豌豆修尾蚜为食的种群;取食棉蚜、桃蚜和豌豆修尾蚜的方斑瓢虫种群内禀增长率分别为0.216 9、0.212 5和0.044 3,种群趋势指数分别为164.10、130.93和20.98,以棉蚜和桃蚜为食的方斑瓢虫种群增长趋势均显著高于饲喂豌豆修尾蚜的种群。综合以上各项参数,棉蚜和桃蚜是方斑瓢虫的适宜天然猎物。其中,桃蚜规模饲养更为便捷,成本较低,是方斑瓢虫规模化扩繁的优选猎物。研究结果对方斑瓢虫的规模化人工饲养及释放应用具有重要的...     

安徽省农区害鼠数量消长动态的初步研究

安徽省是全国粮食主产省份之一。全省现有耕地420万hm2以上,其中小麦、水稻等作物常年种植面积分别为187万hm2、213万hm2。同时又是1个人口大省,现有农户1 600万户以上。全省农区(农田、农舍)害鼠发生较为严重。据统计,常年发生鼠害面积农田约80万hm2,农户害鼠发生普遍率达80%以上,农区害鼠密度较高(百夹捕获率),平均农田为4.77%,农舍为7.73%。2003年全省实施农区统一灭鼠。近2年来,通过对贵池市、和县、霍邱县、宁国市、利辛县、屯溪区、萧县等全省鼠情监测点监测结果进行了系统研究。1害鼠发生种类本省农区害鼠有褐家鼠(Rattus norvegicu…     

中国重要外来物种紫茎泽兰的研究现状

紫茎泽兰曾被作为观赏性植物引入欧洲、澳洲、南美洲、亚洲等地,如今却成为我国最具侵害性的杂草之一。本文综述了外来恶性杂草紫茎泽兰的植物学特征、分布、入侵机制、危害性,以及对它的防除与综合利用。