第一篇：
机经：Venus和地球的联系，区别和不同
解析：这套题是天文主题。了解部分背景知识对解题有提速作用。
另，阅读涉及区别和联系的文章，需对相关逻辑关系词有较好把握。
Venus compared with the Earth
Venus is often named as Earth's twin because both worlds share a similar size, surface composition and have an atmosphere with a complex weather system.
The figure on the right compares Venus and Earth spacecraft images. The surface of Venus is shown in orange as radar images while the atmosphere is reproduced on near true colors as it would be seen by the human eye. The upper clouds are brightest in the blue and ultraviolet wavelengths making Venus a white-blue colour planet. Both planets have almost the same size and density and Venus is only a 30% closer to the Sun than Earth. Both share an interesting geological evolution with old volcanoes in Venus and some of them could still be active. One of the biggest misteries of Venus is why its surface is so young on geological time-scales. It is interesting to remark that there is almost no water on Venus' atmosphere.
There are many more differences between both planets.
Whereas Earth rotates in about 24 hours Venus rotates in the contrary sense (retrograde rotation) in 243 days. The orbital period of Venus is 225 days so that a Venus year takes less than a full day. The combination of these two periods results in the Sun appearing from the West and dissapearing over the East with a day-night cycle of 117 days.
The atmosphere of Venus is 90 times more dense than that on Earth and it is made of 96.5% of CO2 and a 3% of nitrogen. This means that both planets have the same amount of Nitrogen on their atmospheres. Surprinsingly the CO2 on Earth is stored on calcite type rocks and if we would convert the CO2 on these rocks into atmospheric CO2 it would amount to the same amount of CO2 that there is on Venus' atmosphere.
Because of the denser atmosphere and the chemical composition Venus experiences an inmense green-house effect that raises the temperature over the surface to more than 470.
The figure on the right illustrates the basics of the greenhouse effect on Venus. Long-wave radiation from the Sun is mainly reflected at the upper cloud deck and partially absorbed by the atmosphere but part of it reaches the surface and heats the lowest atmosphere. The hot surface cools down emitting short-wave radiation that is absorbed and re-emitted by the green-house gases of the atmosphere impeding cooling of the planet and originating the high temperatures at the surface. Figure extracted from here.
Clouds are common on Earth but they cover completely Venus' atmosphere. They are made of sulfuric acid droplets at 50-70 km above the surface and at temperatures comparables to Earth's surface temperatures. They are extremely reflective making Venus the most reflecting body in the Solar System.
第二篇：
机经： 美索不达米亚地区灌溉系统 灌溉系统发展导致洪水和盐碱地 洪水盐碱地的治理方式 及梯田的开发，水土保持。
解析：涉及考古和历史类的文章，需对时间顺序有较强把握。按时间链走的文章，部分段落的主题信息比较容易分散在段落中，而不是在第一句中整体体现。所以进行整段概括的同时，需要关注是否有转折信息。
Mesopotamia: Canals on the Plain
Irrigation has been an important base for agriculture in Mesopotamia (what is now Iraq and part of Iran) for 6000 years. But Mesopotamia is very different from Egypt. Mesopotamia has low rainfall, and is supplied with surface water by only two major rivers, the Tigris and the Euphrates. Although they are much smaller than of the Nile, they have much more dramatic spring floods, from snowmelt in the highlands of Anatolia, and they carry more silt. Furthermore, the plains of Mesopotamia are very flat, and poorly drained, so that the region has always had persistent problems with poor soil, drought, catastrophic flooding, silting, and soil salinity.
Mesopotamian engineers had to worry about water storage and flood control as well as irrigation. Silt built up quickly in the canals, threatening to choke them. This could be overcome by constant dredging as long as organization and manpower were available. The other problem was more insidious, and could not be overcome by the engineering available at the time. It was difficult to drain water off the fields, and there was always a tendency for salt to build up in the soil.
Although the plain of Mesopotamia is very flat, the bed of the Euphrates is higher than that of the Tigris; in fact, Euphrates floods sometimes found their way across country into the Tigris. Engineers used this gradient as soon as irrigation schemes became large enough, using the Euphrates water as the supply, and the Tigris channel as a drain.
Mesopotamia has had times of successful irrigation, and times of silt and salinity crises: the latter around 2000 BC, 1100 BC, and after 1200 AD. The first crisis may have been caused by water politics. In any irrigation system, the farmers most downstream are those most likely to be short of water in a dry year, or to receive the most polluted water. In Sumeria, the city of Lagash was rather far downstream in the canal system based on the Euphrates. Apparently Entemanna of Lagash decided that he would instead cut a canal to tap Tigris water, but the addition of poor-quality water led to rapid salinization of the soil.
Sumeria
The earliest city-states of Mesopotamia, those of Sumeria, lay in the lowest, most water-rich areas of what is now southern Iraq. Irrigation could be fairly simple in this region, with each city-state probably building one irrigation system. The cities may have originally been administrative centers, marketing centers, and defensive centers related to local irrigation schemes: in other words, they were "irrigation cities".
From time to time catastrophic floods overwhelmed the region. At Ur there is a well-known band of 1.5 m of clay between two layers of pottery. This is evidence of a major flood, and this event was probably the basis for the flood story in the Sumerian Epic of Gilgamesh and for the much later Biblical story of the Flood.
Mesopotamian engineers built very large weirs and diversion dams, to create reservoirs and to supply canals that carried water considerable distances across the flat countryside. The scale of their irrigation was larger than in Egypt, and Mesopotamian irrigation was interventionist and active. Almost certainly the idea of diversion dams was brought to Mesopotamia from the hills, since the rivers are mostly perennial. Mesopotamian tradition suggests so: Sargon of Assyria, probably learned it from the ancient nation of Urartu. The scale and ambition of early Iron Age Mesopotamian projects was matched only in China and Egypt.
The Abassids
After the wave of Moslem expansion broke over Mesopotamia, the Abassid Caliphate was based on Baghdad from 762 AD until its demise in 1258. Existing irrigation schemes were renovated and greatly extended in very large projects. Abassid engineers drew water from the Euphrates at five separate points, and led it in parallel canals across the plains, watering a huge area south of Baghdad. This system provided the basis for the enormously rich culture of Baghdad, which is still remembered in legend (Scheherezade, the Caliph of Baghdad, and the Arabian Nights) as well as history. But it required a lot of physical maintenance, and there was a lot of salinization in the south. As central government began to fail in the 12th century (mostly from extravagant overspending), the canals became silt-choked, the irrigation system deteriorated, and the lands became more salinized. The deathblow to the system was natural: massive floods about 1200 AD shifted the courses of both the Tigris and the Euphrates, cutting off most of the water supply to the Nahrwan Canal and wrecking the whole system. The Abbasids were too weak (or bankrupt) by now to institute repairs, and the agricultural system collapsed. By the time the Mongols under Hulagu devastated Iraq and Baghdad in 1258 AD, they were finishing off a society that was already a wasteland. Iraq has remained a desert for more than 600 years.
第三篇：
机经：
太平洋地区 火山地质活动形成的岛上的物种的传播 鸟风浪传播 及影响分布的4个原因
分析：生物多样性是一个很经典的主题。这篇文章相当于一篇较多主题综合的文章。但由于背景知识的简单性，所以不会对考生造成太多干扰。
相关背景：
What is Island Biodiversity?
An explanation of island biodiversity should start with a definition of islands. Yet this definition is elusive. Although we can all agree that an island, strictly speaking, is a piece of land surrounded by water, beyond this stiupulation, there is no single accepted definition. The Millennium Ecosystem Assessment, for example, defines islands as “lands isolated by surrounding water and with a high proportion of coast to hinterland”; stipulates that they must be populated, separated from the mainland by a distance of at least two kilometres, and measure between 0.15 square kilometres and the size of Greenland (2.2 million square kilometres). Islands located within seas can be categorized in many ways, including by their area; by their altitude into high and low-lying islands; by a combination of the size of the land area, and political and demographic criteria to identify small island developing States; by their distance from the nearest continent; whether there are inhabited or not; the number of inhabitants; or whether they are continental (land areas that used to be connected to the mainland) or oceanic (those that rose from the sea as a result of coral deposits, volcanic activity or tectonic forces) islands. At the SCBD, work on island biodiversity emphasizes oceanic islands and particularly small island developing States (SIDS) because these systems are often perceived to be the most at risk.
In terms of biodiversity, the issue is clearer: islands boast a truly unique assemblage of life. Species become island dwellers either by drifting on islands, like castaways, as they break off from larger landmasses (in the case of continental islands) or by dispersing across the ocean to islands newly emerged from the ocean floor (oceanic islands). Henceforth they are confined to small, isolated areas located some distance from other large landmasses. Over time, this isolation exerts unique evolutionary forces that result in the development of a distinct genetic reservoir and the emergence of highly specialized species with entirely new characteristics and the occurrence of unusual adaptations, such as gigantism, dwarfism, flightlessness, and loss of dispersability and defence mechanisms. Genetic diversity and population sizes tend to be limited, and species often become concentrated in small confined areas.
The legacy of a unique evolutionary history, many island species are endemic—found nowhere else on Earth. Islands harbour higher concentrations of endemic species than do continents, and the number and proportion of endemics rises with increasing isolation, island size and topographic variety. For example, over 90% of Hawaiian island species are endemic. In Mauritius, some 50% of all higher plants, mammals, birds, reptiles and amphibians are endemic, and the Seychelles has the highest level of amphibian endemism in the world. The island of Cuba is home to 18 endemic mammals, while mainland Guatemala and Honduras, both nearby, have only three each. Madagascar is home to more than 8000 endemic species, making it the nation with the highest number of endemic species in sub-Saharan Africa.
It has often been remarked that islands make a contribution to global biodiversity that is out of proportion to their land area. In this sense, they can be thought of collectively as biodiversity “hot spots”, containing some of the richest reservoirs of plants and animals on Earth.#p#副标题#e#
第二套：
第一篇：Origins of writing
机经版本一：
先说writing的材料，主要讲了一个中东地区的S民族，这个民族发明了一种Clay，非常耐用，适合长期保存。
同时说了，Egypt 也有自己的发展， 叫什么reed做的东西，这种东西有缺点，就是像现在的纸一样容易碎。(有题，问为什么说埃及人用这种材料)
然后讲Clay的好处，说是传遍地中海，全都使用这种材料。后来这个S被他国占领了，语言也被别的国家抢去了，word 和sound都变了意义。但是literature没变。 就像Latin语，罗马帝国退去，Latin的文字形式还是保存下来。但是这种东西很难学，需要train，只有少数S族几个人会(这些都是考题)。
然后讲people用writing干什么，就是一个evolution过程，最开始是记一些东西的数量，后来变成了记载国家大事，商业帐本，之类的比较琐碎的日常东西。
再讲clay这个东西经久耐用，现在出土的问题都保存得比较好，所以学者们都很喜欢这些东西，因为要研究。Clay这个东西经常能挖出来。
词汇题：key, virtue, now and then
机经版本二：
这篇文章里有好多学术词，实在不记得了。有两种人，A。。。S。。。埃及人刚开始在一种叫做papyrus的材料写字，这种材料有个缺点就是fragile，especially 容易be destroyed by fires. 所以后来开始使用S人创造的一种材料，埃及人给这种材料创造了sounds和words.
解析：苏美尔是常考主题。由于涉及时间，读文章时一定要有主观意识去自行概括主题。
The Sumerians were one of the earliest urban societies to emerge in the world, in Southern Mesopotamia more than 5000 years ago. They developed a writing system whose wedge-shaped strokes would influence the style of scripts in the same geographical area for the next 3000 years. Eventually, all of these diverse writing systems, which encompass both logophonetic, consonantal alphabetic, and syllabic systems, became known as cuneiform.
It is actually possible to trace the long road of the invention of the Sumerian writing system. For 5000 years before the appearance of writing in Mesopotamia, there were small clay objects in abstract shapes, called clay tokens, which were apparently used for counting agricultural and manufactured goods. As time went by, the ancient Mesopotamians realized that they needed a way to keep all the clay tokens securely together (to prevent loss, theft, etc), so they started putting multiple clay tokens into a large, hollow clay container which they then sealed up. However, once sealed, the problem of remembering how many tokens were inside the container arose. To solve this problem, the Mesopotamians started impressing pictures of the clay tokens on the surface of the clay container with a stylus. Also, if there were five clay tokens inside, they would impress the picture of the token five times, and so problem of what and how many inside the container was solved.
Subsequently, the ancient Mesopotamians stopped using clay tokens altogether, and simply impressed the symbol of the clay tokens on wet clay surfaces. In addition to symbols derived from clay tokens, they also added other symbols that were more pictographic in nature, i.e. they resemble the natural object they represent. Moreover, instead of repeating the same picture over and over again to represent multiple objects of the same type, they used diferent kinds of small marks to "count" the number of objects, thus adding a system for enumerating objects to their incipient system of symbols. Examples of this early system represents some of the earliest texts found in the Sumerian cities of Uruk and Jamdat Nasr around 3300 BCE, such as the one below.
The Sumerian writing system during the early periods was constantly in flux. The original direction of writing was from top to bottom, but for reasons unknown, it changed to left-to-right very early on (perhaps around 3000 BCE). This also affected the orientation of the signs by rotating all of them 90° counterclockwise. Another change in this early system involved the "style" of the signs. The early signs were more "linear" in that the strokes making up the signs were lines and curves. But starting after 3000 BCE these strokes started to evolve into wedges, thus changing the visual style of the signs from linear to "cuneiform".
第二篇：The Commercial Revolution
机经版本一：
中世纪欧洲贸易。银币，后来人们使用新的贸易方式，信用记帐等，对资本主义产生很大刺激。还讲了一个人从德国小镇开始的冒险之旅。
机经版本二：
第一方面：商业的发展带来了交通的发展。correspondence or transportation
第二方面：the transaction and mutual trust increase the development of credit or acounting financial system
第三方面：promote the urbanization from rural characteristics
解析：历史题材是一个非常大的考点。对于这种类型文章不熟悉的同学，应该多做一些该类型文章的精读训练，尽可能的抵消学科恐惧感。
相关背景知识：
The history of capitalism can be traced back to early forms of merchant capitalism practiced in Western Europe during theMiddle Ages.[1] It began to develop into its modern form during the Early Modern period in the Protestant countries of North-Western Europe, especially the Netherlands and England. Traders in Amsterdam and London created the first chartered joint-stock companies driving up commerce and trade, and the first stock exchanges and banking and insurance institutions were established.[2]
Over the course of the past five hundred years, capital has been accumulated by a variety of different methods, in a variety of scales, and associated with a great deal of variation in the concentration of economic power and wealth.[3] Much of the history of the past five hundred years is concerned with the development of capitalism in its various forms.
Crisis of the 14th century
According to some historians, the modern capitalist system has its origin in the "crisis of the fourteenth century," a conflict between the land-owning aristocracy and the agricultural producers, the serfs. Manorial arrangements inhibited the development of capitalism in a number of ways. Because serfs were forced to produce for lords, they had no interest in technological innovation; because serfs produced to sustain their own families, they had no interest in co-operating with one another. Because lords owned the land, they relied on force to guarantee that they were provided with sufficient food. Because lords were not producing to sell on the market, there was no competitive pressure for them to innovate. Finally, because lords expanded their power and wealth through military means, they spent their wealth on military equipment or onconspicuous consumption that helped foster alliances with other lords; they had no incentive to invest in developing new productive technologies.[5]
This arrangement was shaken by the demographic crisis of the 14th century. This crisis had several causes: agricultural productivity reached its technological limitations and stopped growing; bad weather led to the Great Famine of 1315–1317; the Black Death in 1348–1350 led to a population crash. These factors led to a decline in agricultural production. In response feudal lords sought to expand agricultural production by expanding their domains through warfare; they therefore demanded more tribute from their serfs to pay for military expenses. In England, many serfs rebelled. Some moved to towns, some purchased land, and some entered into favorable contracts to rent lands from lords who needed to repopulate their estates.[6]
The collapse of the manorial system in England created a class of tenant-farmers with more freedom to market their goods and thus more incentive to invest in new technologies. Lords who did not want to rely on rents could buy out or evict tenant farmers, but then had to hire free-labor to work their estates – giving them an incentive to invest in two very different kinds of commodity owners; on the one hand, the owners of money, means of production, means of subsistence, who are eager to valorize the sum of value they have appropriated by buying the labour power of others; on the other hand, free workers, the sellers of their own labor-power, and, Free workers, in the double sense that they neither form part of the means of production nor do they own the means of production that transformed land and even money into what we now call "capital."[7] Marx labeled this period the "pre-history of capitalism".[8]
It was, in effect, feudalism that began to lay some of the foundations necessary for the development of mercantilism, a precursor to capitalism. Feudalism took place mostly in Europe and lasted from the medieval period up through the 16th century. Feudal manors were almost entirely self-sufficient, and therefore limited the role of the market. This stifled the growth of capitalism. However, the relatively sudden emergence of new technologies and discoveries, particularly in the industries of agriculture[9] and exploration, revitalized the growth of capitalism. The most important development at the end of Feudalism was the emergence of "the dichotomy between wage earners and capitalist merchants".[10] With mercantilism, the competitive nature means there are always winners and losers, and this is clearly evident as feudalism transitions into mercantilism, an economic system characterized by private or corporate ownership of capital goods, by investments that are determined by private decision, and by prices, production, and the distribution of goods that are determined mainly by competition in a free market.
Rise of towns
The transition from the feudal organization of society to early forms of capitalism happened in periods differing from country to country. According to Cambridge political philosopher and historian Quentin Skinner, the towns of North Italy were the first urbanised parts of Europe from the 12th century. German bishop Otto of Freising recorded the growth of town life there, the loyalty of landed nobility to town authorities, and the emergence of republicanism and belief in civic liberty.[11]
Agrarian capitalism and enclosure
Decaying hedges mark the lines of the straight field boundaries created by a Parliamentary Act of Enclosure.
England in the sixteenth century was already a centralized state, in which much of the feudal order of Medieval Europe had been swept away. This centralization was strengthened by a good system of roads and a disproportionately large capital city,London. The capital acted as a central market hub for the entire country, creating a very large internal market for goods, instead of the fragmented feudal holdings that prevailed in most parts of the Continent. The economic foundations of the agricultural system were also beginning to diverge substantially; the manorial system had broken down by this time, and land began to be concentrated in the hands of fewer landlords with increasingly large estates. Instead of a serf-based system of labour, workers were being employed as part of a broader and expanding money economy. The system put pressure on both the landlords and the tenants to increase the productivity of the agriculture to make profit; the weakened coercive power of the aristocracy to extract peasant surpluses encouraged them to try out better methods, and the tenants also had incentive to improve their methods, in order to flourish in an increasingly competitive labour market. Terms of rent for the land were becoming subject to economic market forces rather than the previous stagnant system of custom and feudal obligation.[12]
An important aspect of this process was the enclosure[13] of the common land held in the open field system where peasants had traditional rights, such as mowing meadows for hay and grazing livestock. Once enclosed, these uses of the land became restricted to the owner, and it ceased to be land for commons. The process of enclosure began to be a widespread feature of the English agricultural landscape during the 16th century. By the 19th century, unenclosed commons had become largely restricted to rough pasture in mountainous areas and to relatively small parts of the lowlands.
Marxist and neo-Marxist historians argue that rich landowners used their control of state processes to appropriate public land for their private benefit. This created a landlessworking class that provided the labour required in the new industries developing in the north of England. For example: "In agriculture the years between 1760 and 1820 are the years of wholesale enclosure in which, in village after village, common rights are lost".[14] "Enclosure (when all the sophistications are allowed for) was a plain enough case of class robbery".[15]
Other scholars[16] argue that the better-off members of the European peasantry encouraged and participated actively in enclosure, seeking to end the perpetual poverty ofsubsistence farming. "We should be careful not to ascribe to [enclosure] developments that were the consequence of a much broader and more complex process of historical change."[17] "[T]he impact of eighteenth and nineteenth century enclosure has been grossly exaggerated...."
第三篇：The stability of ecosystem
机经版本一：生物多样性对整个生态圈的影响。讲了一个在明尼苏达的grassland实验，成为了diversity让ecosystem stable的evidence。然后又开始老套路不sufficient啊还需要更多research啊blablabla。很简单。
机经版本二： 主要讲the relationship between diversity of species with the stability of ecosystem. 主要表达了the lost of one species can destroy the entire system.
解析：这篇文章难度不大。主题是大家所熟悉的生物多样性。建议阅读相关OG文章：The Long-Term Stability of Ecosystems.
背景资料：
Ecological effects of biodiversity
The diversity of species and genes in ecological communities affects the functioning of these communities. These ecological effects of biodiversity in turn affect both climate change through enhanced greenhouse gases, aerosols and loss of land cover, and biological diversity, causing a rapid loss of ecosystems and extinctions of species and local populations. The current rate of extinction is sometimes considered a mass extinction, with current species extinction rates on the order of 100 to 1000 times as high as in the past.
The two main areas where the effects of biodiversity on ecosystem function have been studied are the relationship between diversity and productivity, and the relationship between diversity and community stability. More biologically diverse communities appear to be more productive (in terms of biomass production) than are less diverse communities, and they appear to be more stable in the face of perturbations. Also animals that inhabit an area may alter the surviving conditions by factors assimilated by climate.
In order to understand the effects that changes in biodiversity will have on ecosystem functioning, it is important to define some terms. Biodiversity is not easily defined, but may be thought of as the number and/or evenness of genes, species, and ecosystems in a region. This definition includes genetic diversity, or the diversity of genes within a species, species diversity, or the diversity of species within a habitat or region, and ecosystem diversity, or the diversity of habitats within a region.
Two things commonly measured in relation to changes in diversity are productivity and stability. Productivity is a measure of ecosystem function. It is generally measured by taking the total aboveground biomass of all plants in an area. Many assume that it can be used as a general indicator of ecosystem function and that total resource use and other indicators of ecosystem function are correlated with productivity.
Stability is much more difficult to define, but can be generally thought of in two ways. General stability of a population is a measure that assumes stability is higher if there is less of a chance of extinction. This kind of stability is generally measured by measuring the variability of aggregate community properties, like total biomass, over time. The other definition of stability is a measure of resilience and resistance, where an ecosystem that returns quickly to an equilibrium after a perturbation or resists invasion is thought of as more stable than one that doesn't.
Review of data
Field experiments to test the degree to which diversity affects community productivity have had variable results, but many long term studies in grassland ecosystems have found that diversity does indeed enhance the productivity of ecosystems. Additionally, evidence of this relationship has also been found in grassland microcosms. The differing results between studies may partially be attributable to their reliance on samples with equal species diversities rather than species diversities that mirror those observed in the environment. A 2006 experiment utilizing a realistic variation in species composition for its grassland samples found a positive correlation between increased diversity and increased production.
However, these studies have come to different conclusions as to whether the cause was due more to diversity or to species composition. Specifically, a diversity in the functional roles of the species may be a more important quality for predicting productivity than the diversity in species number. Recent mathematical models have highlighted the importance of ecological context in unraveling this problem. Some models have indicated the importance of disturbance rates and spatial heterogeneity of the environment, others have indicated that the time since disturbance and the habitat's carrying capacity can cause differing relationships. Each ecological context should yield not only a different relationship, but a different contribution to the relationship due to diversity and to composition. The current consensus holds at least that certain combinations of species provide increased community productivity.
Future research
In order to correctly identify the consequences of diversity on productivity and other ecosystem processes, many things must happen. First, it is imperative that scientists stop looking for a single relationship. It is obvious now from the models, the data, and the theory that there is no one overarching effect of diversity on productivity. Scientists must try to quantify the differences between composition effect and diversity effects, as many experiments never quantify the final realized species diversity (instead only counting numbers of species of seeds planted) and confound a sampling effect for facilitators (a compositional factor) with diversity effects.
Relative amounts of overyielding (or how much more a species grows when grown with other species than it does in monoculture) should be used rather than absolute amounts as relative overyielding can give clues as to the mechanism by which diversity is influencing productivity, however if experimental protocols are incomplete, one may be able to indicate the existence of a complementary or facilitative effect in the experiment, but not be able to recognize its cause. Experimenters should know what the goal of their experiment is, that is, whether it is meant to inform natural or managed ecosystems, as the sampling effect may only be a real effect of diversity in natural ecosystems (managed ecosystems are composed to maximize complementarity and facilitation regardless of species number). By knowing this, they should be able to choose spatial and temporal scales that are appropriate for their experiment. Lastly, to resolve the diversity-function debate, it is advisable that experiments be done with large amounts of spatial and resource heterogeneity and environmental fluctuation over time, as these types of experiments should be able to demonstrate the diversity-function relationship more easily.
Biodiversity (Experiment E120)
Experiment 120 Data
Introduction
This experiment (often called the "Big" Biodiversity Experiment; the "small" experiment is no longer maintained) determines effects of plant species numbers and functional traits on community and ecosystem dynamics and functioning. It manipulates the number of plant species in 168 plots, each 9 m x 9 m, by imposing plant species numbers of 1, 2, 4, 8, or 16 perennial grassland species. The species planted in a plot were randomly chosen from a pool of 18 species (4 species, each, of C4 grasses, C3 grasses, legumes, non-legume forbs; 2 species of woody plants). Its high replication (about 35 plots at each level of diversity) and large plots allow observation of responses of herbivorous, parasitoid and predator insects and allow additional treatments to be nested within plots. Planted in 1994, it has been annually sampled since 1996 for plant aboveground biomass and plant species abundances and for insect diversity and species abundances. Root mass, soil nitrate, light interception, biomass of invading plant species, and C and N levels in soils, roots, and aboveground biomass have been determined periodically. In addition, soil microbial processes and abundances of mycorrhizal fungi, soil bacteria and other fungi, N mineralization rates, patterns of N uptake by various species, and invading plant species, have been periodically measured in subprojects in the Biodiversity Experiment.
Key Results
Plant biomass production increased with diversity (Fig 1) because of complementary interactions among species and not because of selection (sampling) effects (Figs 2 Tilman et al. 2001b, Pacala and Tilman 2002, Hille Ris Lambers et al. 2004; Fargione et al. in prep.).
Foliar fungal disease incidence decreased at higher diversity because of greater distance between individuals of a species, and resultant lower rates of disease spread (Mitchell et al. 2002).
Greater plant diversity led to greater diversity of herbivorous insects, and this effect continued up the food web to predator and parasitoid insects (Haddad et al. 2001).
Fewer novel plant species invaded higher diversity treatments because of their lower soil NO3 levels, greater neighborhood crowding and competition, and greater chance that functionally similar species would occur in a given neighborhood (Figs 3; Naeem et al. 2000, Kennedy et al. 2002, Fargione et al. 2003, Fargione and Tilman 2005a, 2005b).
Greater plant species numbers led to greater ecosystem stability (lower year-to-year variation in total plant biomass) but to lower species stability (greater year-to-year variation in abundances of individual species), with the stabilizing effect of diversity mainly attributable to statistical averaging effects and overyielding effects (Fig 4; Tilman et al, submitted).
Data gathered this past field season shows that soil total C has now become an increasing function of plant species numbers (Fig 5).
Our results have helped resolve a debate about why plant diversity affects ecosystem functioning. Such resolution was accomplished by a Paris symposium in which we made CDR biodiversity data available so others could test their alternative hypotheses; by a paper by 12 ecologists with divergent views that explored areas of agreement and articulated areas in need of 10 further testing (Loreau et al. 2001); and by our analyses of alternative hypotheses using results of the CDR biodiversity experiment (Tilman et al. 2001b).
第二 套的词汇题：key, colossal, significant, radically, redundance