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1.
不同MT-06发酵液、孢子液和菌液防治黄瓜白粉病的盆栽试验研究发现:不同浓度梯度MT-06制剂对黄瓜白粉病都有抑制作用。MT-06菌液10倍稀释液处理3 d后的保护效果和治疗效果分别达到87.86%和84.89%,与对照三唑酮的处理效果相当,但处理11 d后MT-06菌液10倍稀释液的治疗效果显著高于三唑酮处理(P<0.05),其他处理防治效果都未能达到三唑酮的防治效果。MT-06菌液和孢子液表现防效较MT-06发酵液持久。MT-06定殖试验表明:叶柄上的定殖率仅1×105个.mL-1MT-06孢子液为85%,其余孢子液及菌液处理定殖率均为100%;MT-06在叶片上定殖率较低,MT-06菌液10倍稀释液的定殖率最高为40%。分析认为MT-06防效的保持性较好可能与其能定殖于植物上有关。 相似文献
2.
鄱阳湖砂山地区地表环境结构与其植物多样性的变化 总被引：1，自引：0，他引：1
该文对鄱阳湖砂山地区地表环境结构和土地风沙化过程中物种多样性的变化特征进行了分析,依据植物种在各类型风沙化土地出现的频率与不同风沙化阶段各生活型植物种的组成,探讨了风沙化过程中植物种绝灭与定居的特点.物种多样性指数分析表明:风沙化过程是物种多样性衰减的过程,风沙化首先导致特有种的灭绝,其次为稀有种.从植物的生活型来看,多年生草本与乔木类植物受风沙化影响最大,而灌木类植物可存活风沙化过程各个阶段,在风沙化过程中植物种的绝灭速率大于定居速率.要建立有恢复力的砂山景观生态系统,进行生态重组,既需要在砂山地区内也需要在砂山地区外的生态存储,现实情况也需要这种双重存储的生态学准备. 相似文献
3.
L. J. Wiles 《Precision Agriculture》2009,10(3):277-290
Site-specific weed management can include both limiting herbicide application to areas of the field where weed pressure is
above the economic threshold (patch spraying) and varying the choice of herbicide for most cost-effective weed control of
local populations. The benefits of patch spraying with several, postemergence herbicides in irrigated corn were evaluated
in simulation studies using weed counts from 16 fields. Patch spraying with one, two or the number of herbicides that maximized
net return for a field was simulated. With patch spraying of one herbicide, the average area of a field left untreated is
34.5%. Net return increases by $3.09 ha−1 compared to a uniform application without decreasing crop yield. Additional herbicides increase the average benefits with
just 4% more of the field treated. With two herbicides, the increase in net return is almost tripled and herbicide use is
reduced nearly 10-fold compared to patch spraying with one herbicide, and weed control is better than the uniform application
in 10 fields. Using more than two herbicides for patch spraying further reduces weed escapes, but herbicide use is greater
than a uniform application in 10 fields. Growers might be more willing to adopt patch spraying if more than one herbicide
is used in a field. 相似文献
4.
建立了一个带饱和发生率的随机HIV模型.首先分析了全局正解的存在性和有界性,进一步通过构造Lyapunov函数得到了病毒灭绝和持续的条件. 相似文献
5.
Because individual species can play key roles, the loss of species through extinction or their gain through colonization can cause major changes in ecosystems. For almost 20 years after kangaroo rats were experimentally removed from a Chihuahuan desert ecosystem in the United States, other rodent species were unable to compensate and use the available resources. This changed abruptly in 1995, when an alien species of pocket mouse colonized the ecosystem, used most of the available resources, and compensated almost completely for the missing kangaroo rats. These results demonstrate the importance of individual species and of colonization and extinction events in the structure and dynamics of ecosystems. 相似文献
6.
We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles. 相似文献
7.
Martin PS 《Science (New York, N.Y.)》1973,179(4077):969-974
I propose a new scenario for the discovery of America. By analogy with other successful animal invasions, one may assume that the discovery of the New World triggered a human population explosion. The invading hunters attained their highest population density along a front that swept from Canada to the Gulf of Mexico in 350 years, and on to the tip of South America in roughly 1000 years. A sharp drop in human population soon followed as major prey animals declined to extinction. Possible values for the model include an average frontal depth of 160 kilometers, an average population density of 0.4 person per square kilometer on the front and of 0.04 person per square kilometer behind the front, and an average rate of frontal advance of 16 kilometers per year. For the first two centuries the maximum rate of growth may have equaled the historic maximum of 3.4 percent annually. During the episode of faunal extinctions, the population of North America need not have exceeded 600,000 people at any one time. The model generates a population sufficiently large to overkill a biomass of Pleistocene large animals averaging 9 metric tons per square kilometer (50 animal units per section) or 2.3 x 10(8) metric tons in the hemisphere. It requires that on the front one person in four destroy one animal unit (450 kilograms) per week, or 26 percent of the biomass of an average section in 1 year in any one region. Extinction would occur within a decade. There was insufficient time for the fauna to learn defensive behaviors, or for more than a few kill sites to be buried and preserved for the archeologist. Should the model survive future findings, it will mean that the extinction chronology of the Pleistocene megafauna can be used to map the spread of Homo sapiens throughout the New World. 相似文献
8.
[目的]对不同株型水稻冠层结构、冠层内光分布和光合作用之间的定量化关系进行了模拟计算研究。[方法]采用双参数椭圆函数和Beer-Lambert光传播定律分直射光和散射光对作物的冠层结构和光分布进行了数值模拟。[结果]函数模拟值与实测值的曲线变化趋势一致。两优培九的模拟值与实测值变化较为一致。但是汕优63无论是直射光还是散射光,均表现为在冠层上方实测值比模拟值大,而在冠层下方模拟值比实测值大。通过对消光系数的模拟研究表明,9:00～17:00两优培九直射光消光系数要比汕优63平均小0.45,而散射光消光系数两优培九为0.34,汕优63为0.38。[结论]在一定环境下,作物叶倾角分布密度的差异程度决定了冠层光分布差异的大小,因此,将消光系数视为常数是不适当的;可以在冠层光分布模型的基础上进一步建立冠层光合作用的数值模型,进而估算作物的生产潜力,为作物育种与栽培提供科学依据。 相似文献
9.
利用采自宁夏银川市金凤区和西夏区两个枸杞栽培区0~20、20~40和40~60 cm共3个土层深度的枸杞根系和根围土样，研究枸杞 (Lycium barbarum)根系深色有隔内生真菌 (dark septate endophytes，DSE)的定殖规律及其与土壤因子的相关性，以期为充分利用DSE资源和基于生物技术促进荒漠植被恢复和生态改良提供依据。结果表明，DSE可定殖于枸杞根系形成深色、有隔菌丝，微菌核多呈聚合型和离散型。两样地DSE定殖率差异显著，金凤区样地DSE平均总定殖率（73.27%）显著高于西夏区样地 （23.54%）；不同土层DSE定殖率有差异，两样地DSE总定殖率、菌丝定殖率和微菌核定殖率最大值均出现在20~40 cm土层。两样地不同土层深度间土壤因子的分布差异显著，主成分分析显示pH、碱解氮、速效磷、有机质、碱性磷酸酶和蔗糖酶能综合反映银川市两枸杞样地根际土壤养分状况。方差分解分析结果表明，DSE定殖受到样地和土壤因子的共同影响。相关性分析表明，DSE定殖在两样地间存在较大差异，金凤区样地DSE总定殖率与有机质显著正相关，与速效钾极显著负相关；DSE菌丝定殖率与有机质、速效磷和碱解氮显著正相关，与速效钾和pH显著负相关。西夏区样地DSE总定殖率和微菌核定殖率与pH极显著正相关；DSE菌丝定殖率与有机质、速效磷和脲酶显著负相关。上述结果说明，枸杞根系能被DSE侵染，DSE定殖具有明显的垂直空间异质性，并与土壤因子密切相关。 相似文献
10.
在遥感和GIS技术支持下,基于1975-2010年长时间序列遥感影像,选取斑块密度指数(PD)、景观内部生境面积指数(IA)、斑块平均面积指数(MPS)、斑块形状破碎化指数(FS1、FS2)等具有典型生态意义的景观指数模型,系统分析了黑河中游湿地景观的破碎化过程,并结合灰色关联分析、主成分分析等方法,探讨了影响研究区湿地景观破碎化过程的各驱动因子。结果表明:近35年来,研究区湿地景观破碎化主要表现为斑块平均面积的萎缩,斑块密度的上升以及斑块形状破碎化指数的增大。整个研究时段内,研究区湿地斑块平均面积减少了48.95hm2,斑块密度的上升0.006个/hm2;导致黑河中游湿地景观破碎化发生和发展的驱动力包含自然和人文两个方面。自然因子对湿地景观破碎化进程的影响则主要体现在气温和降水上,而且气温对湿地景观破碎化进程的影响程度明显大于降水。但在1975-2010年间的这一较小时间尺度上,人类活动对湿地景观破碎化的贡献率明显高于自然因子,人类活动能力的增强以及影响范围的不断扩大是引发黑河中游湿地景观破碎化的主因。 相似文献
11.
The study of past forest change provides a necessary historical context for evaluating the outcome of human-induced climate change and biological invasions. Retrospective analyses based on fossil and genetic data greatly advance our understanding of tree colonization, adaptation, and extinction in response to past climatic change. For instance, these analyses reveal cryptic refugia near or north of continental ice sheets, leading to reevaluation of postglacial tree migration rates. Species extinctions appear to have occurred primarily during periods of high climatic variability. Transoceanic dispersal and colonization in the tropics were widespread at geological time scales, inconsistent with the idea that tropical forests are particularly resistant to biological invasions. 相似文献
12.
《（《农业科学与技术》）编辑部》2017,(8)
13 water quality parameters were tested from 38 reaches of 34 counties in Guizhou where Chinese giant salamander(Andrias davidianus) distributed over the past 30 years. Dissolved oxygen and p H were found to be significant determinants of the species distribution in recent years(P<0.05). There was no Chinese giant salamander distribution in the recent five years in rivers with dissolved solids of greater than 415 mg/L, conductivity of greater than 639 us/cm, salinity of greater than 0.31 ppt and total hardness of greater than 150 mg/L. Sensitive to environment, the Chinese giant salamander is an important indicator for environmental quality, so it could be used as one of the environmental indicator. Eutrophication, chemical fertilizer, pesticides and inorganic pollutants may be one of reasons driving wild CGS into extinction. 相似文献
13.
13 water quality parameters were tested from 38 reaches of 34 counties in Guizhou where Chinese giant salamander (Andrias davidianus ) distributed over the past 30 years. Dissolved oxygen and pH were found to be significant determinants of the species distribution in recent years (P<0.05). There was no Chinese giant salamander distribution in the recent five years in rivers with dissolved solids of greater than 415 mg/L, conductivity of greater than 639 us/cm, salinity of greater than 0.31 ppt and total hardness of greater than 150 mg/L. Sensitive to environment, the Chinese giant salamander is an important indicator for environmental quality, so it could be used as one of the environmental indicator. Eutrophication, chemical fertilizer, pesticides and inorganic pollutants may be one of reasons driving wild CGS into extinction. 相似文献
14.
本溪山樱根部解磷细菌的定殖规律及其对植株生长发育的影响 总被引：2，自引：0，他引：2
【目的】探讨解磷细菌定殖规律及其与本溪山樱地上和地下部生长发育的关系,为土壤管理提供参考依据。【方法】以本溪山樱为研究对象,采用土壤缩影系统并结合常规的分析方法,研究植物促生根际细菌—3株解磷细菌[Bacillus（Y4）、Pseudomonas（J6）、Flavimonas（H7）]于本溪山樱根部的定殖规律及其对根际特征和植株生长发育的影响。【结果】3种菌株定殖部位因时间变化而变化,混接处理中根内没有菌株定殖,但无论单接与混接处理3种菌株定殖密度均随时间延长而降低。接种解磷细菌后,细菌于本溪山樱根部的侵染速度较快,数量较多,放线菌和真菌的侵染能力较低,数量较少。接种Y4可较对照提高植株的净光合速率（Pn）,这种效果随时间的延长逐渐减弱,而接种其它菌液处理均降低了植株的Pn。单接Y4可增加植株中全磷含量。【结论】解磷细菌的定殖数量随外来微生物侵入数量的增多而减少。外来细菌的侵入对解磷细菌的定殖影响较大。处理前期,接种假单胞杆菌（Y4）和芽孢杆菌（J6）对植株生长有一定的促进作用。 相似文献
15.
【目的】明确高产与低产奶牛胎次对产奶量、乳成分和泌乳持续力的影响,为优化奶牛场的饲养管理模式及提高奶牛使用年限提供理论依据。【方法】基于北京、河北等地17个奶牛养殖场共12406头荷斯坦奶牛2021年春季的生产性能测定(DHI)报告,按高产(48.69±6.88 kg/d)和低产(23.47±5.28 kg/d)进行分组,对原数据经预处理后获得5158头高产奶牛和3110头低产奶牛的DHI报告;采用单因素方差分析(One-way ANOVA)进行方差齐性检验,通过Pearson双侧检验进行多变量相关分析,并以LDS和Duncan's多重比较对组间差异进行分析,2个变量间的相关性则通过Spearson相关系数进行判断。【结果】不同胎次对高产与低产奶牛的产奶量、乳成分和泌乳持续力均有影响:高产奶牛3胎和4胎的日产奶量显著高于其他胎次(P<0.05,下同),4胎以上高产奶牛的牛乳体细胞数(SCC)显著高于1胎和2胎高产奶牛;低产奶牛1胎的日产奶量、乳糖率显著高于其他胎次,且SCC显著低于除2胎外的其他胎次。在奶牛泌乳持续力方面,1胎高产奶牛的泌乳持续力显著高于3胎、4胎和5胎,1胎低产奶牛的泌乳持续力显著高于其他胎次,其他胎次间的泌乳持续力均无显著差异(P>0.05,下同);高产与低产奶牛的泌乳持续力与SCC间无显著相关性,但与日产奶量显著相关。除干物质含量与日产奶量、乳脂率与乳糖率的相关性外,高产奶牛和低产奶牛的产奶量、乳成分及SCC间的相关性基本一致,其中,日产奶量与乳糖率呈极显著正相关(P<0.01,下同),与SCC呈极显著负相关,而SCC与乳脂率和乳蛋白率均呈极显著正相关。【结论】高产奶牛最佳使用胎次为3~4胎,低产奶牛最佳使用胎次为1~3胎;高产与低产奶牛的胎次均影响其产奶量、乳成分及泌乳持续力,但不同胎次下产奶量和乳成分的变化趋势存在一定差异。因此,在提高饲养管理水平的基础上,应进一步优化营养供给,及时调整饲粮配方,合理对奶牛进行分群和规划,以达到奶牛的最佳使用胎次,增加养殖经济效益。 相似文献
16.
Blackburn TM Cassey P Duncan RP Evans KL Gaston KJ 《Science (New York, N.Y.)》2004,305(5692):1955-1958
The arrival of humans on oceanic islands has precipitated a wave of extinctions among the islands' native birds. Nevertheless, the magnitude of this extinction event varies markedly between avifaunas. We show that the probability that a bird species has been extirpated from each of 220 oceanic islands is positively correlated with the number of exotic predatory mammal species established on those islands after European colonization and that the effect of these predators is greater on island endemic species. In contrast, the proportions of currently threatened species are independent of the numbers of exotic mammalian predator species, suggesting that the principal threat to island birds has changed through time as species susceptible to exotic predators have been driven extinct. 相似文献
17.
Grigg RW 《Science (New York, N.Y.)》1988,240(4860):1737
The fossil record of shallow marine organisms in the Hawaiian Archipelago and Emperor seamount chain indicates that reef corals were absent during the first half of the Tertiary. Their appearance during the early Oligocene, 34 million years ago, is associated with several paleoceanographic events that appear to have combined to intensify gradually gyral surface currents in the north Pacific. This association suggests that corals were absent in the early Tertiary because of isolation of the Hawaiian Archipelago from the Indo-West Pacific (IWP), the center of reef coral abundance and diversity in the Pacific. Today, the number of species of reef corals in Hawaii is less than 10 percent of the number of species in the IWP. Since their initial colonization, reef corals have been present continuously in the Hawaiian Archipelago, although not without taxonomic change. Episodes of extinction and recolonization are the most likely cause of change in species composition. Recolonization from the IWP may also explain the low rate of endemism (about 20 percent) in the present-day coral fauna. 相似文献
18.
19.
The yield in any given field or management zone is a product of interaction between many soil properties and production inputs. Therefore, multi-year yield maps may give better insight into determining potential management zones. This research was conducted to develop a methodology to delineate yield response zones by using two-state frequency analysis conducted on yield maps for 3 years on two commercial corn fields near Wiggins, Colorado. A zone was identified by the number of years that yield was equal and greater than the average yield in a given year. Classes producing statistically similar yield were combined resulting in three potential yield zones. Results indicated that the variability of yield over time and space could successfully be assessed at the same time without the drawbacks of averaging data from different years. Frequency analysis of multi-year yield data could be an effective way to establish yield response zones. Seventeen percent of the field #1 consistently produced lower yield than the mean while 43 of the field produced yield over the mean. Corresponding values for field #2 were 6% and 42%.The remainder of the fields produced fluctuating yields between years. These spatially and temporally sound yield response maps could be used to identify the yield-limiting factors in zones where yield is either low or fluctuating. Yield response maps could also be helpful to delineate potential management zones with the help of resource zones such as electrical conductivity and soil maps, along with the directed soil sampling results. 相似文献
20.
氮肥运筹与耕法对水稻籽粒增重过程的影响 总被引：1，自引：0，他引：1
应用数学模型Richards方程研究氮肥运筹与耕法对水稻籽粒增重过程的影响。结果表明:不同时期施用氮肥,以粒肥对籽粒增重过程的促进作用最大,而且影响的程度为源限制型品种大于库限制型品种,弱势粒大于强势粒;粒肥施用量(氮素)在0～103.5kg/ha范围内,随着施氮量的增加,籽粒起始灌浆势、最大灌浆速率、平均灌浆速率、活跃灌浆期和生长终值量增加,到达最大灌浆速率的时间缩短,灌浆速率曲线趋向左偏;采用浅、免耕,籽粒在灌浆前期生长比率较大,中、后期生长比率较小,常耕则相反。 相似文献