上海新航道雅思小編發(fā)布劍5Test4雅思閱讀Passage3譯文-The effects of light on plant and animal species，希望幫助考生對照文本更好的研究真題，充分備考，爭取理想成績，實現(xiàn)留學(xué)夢想。

  劍5Test4雅思閱讀Passage3譯文-The effects of light on plant and animal species

  光對動植物的影響

  Light is important to organisms for two different reasons. Firstly it is used as a cue for the timing, of daily and seasonal rhythms in both plants and animals, and secondly it is used to assist growth in plants.

  光對于生物體的重要性是由于兩個不同的原因。第一，光被動植物用作日常時間和季節(jié)節(jié)奏的暗示;第二，光有助于植物生長。

  Breeding in most organisms occurs during a part of the year only, and so a reliable cue is needed to trigger breeding behaviour. Day length is an excellent cue, because it provides a perfectly predictable pattern of change within the year. In the temperate zone in spring, temperatures fluctuate greatly from day to day, but day length increases steadily by a predictable amount. The seasonal impact of day length on physiological responses is called photoperiodism, and the amount of experimental evidence for this phenomenon is considerable. For example, some species of birds’ breeding can be induced even in midwinter simply by increasing day length artificially (Wolfson 1964). Other examples of photoperiodism occur in plants. A short-day plant flowers when the day is less than a certain critical length. A long-day plant flowers after a certain critical day length is exceeded. In both cases the critical day length differs from species to species. Plants which flower after a period of vegetative growth, regardless of photoperiod, are known as day-neutral plants.

  大多數(shù)生物體的繁殖都只發(fā)生在一年中的某些時候，因此，需要一個可靠的提示來引發(fā)繁殖行為。日照長度就是非常好的提示，因為它提供了一個極好的可預(yù)測的一年之中變化的模式。在溫帶的春季，一天與一天之間氣溫波動很大，但是日照長度卻按照可預(yù)測的數(shù)量穩(wěn)步增加。受季節(jié)性影響的日照長度在生理學(xué)上的反應(yīng)叫做光周期現(xiàn)象。這種現(xiàn)象的試驗證據(jù)的數(shù)量相當可觀。例如，僅僅通過人工增加日照長度，一些鳥類甚至在冬至的時候都會被誘發(fā)繁殖(Wolfson, 1964年)。在植物中也有光周期的例子。當日照低于一定的臨界長度，短日照植物會開花。而當日照超過一定的臨界長度時，長日照植物就會開花。在這兩個例子中，臨界日照長度因物種的不同而存在差異。那些不受光周期影響，經(jīng)過一段時間的生長之后便開花的植物叫做日中性植物。

  Breeding seasons in animals such as birds have evolved to occupy the part of the year in which offspring have the greatest chances of survival. Before the breeding season begins, food reserves must be built up to support the energy cost of reproduction, and to provide for young birds both when they are in the nest and after fledging. Thus many temperate-zone birds use the increasing day lengths in spring as a cue to begin the nesting cycle, because this is a point when adequate food resources will be assured.

  諸如鳥類等動物的繁殖期占據(jù)了一年中其后代最有可能生存下來的時間。在繁殖期開始之前，必須儲存足夠的食物以支持繁殖過程中的能量消耗，并且需要為還在巢中和剛長羽毛不久的小鳥提供食物。因此，很多溫帶的鳥類將春季日照長度的增加當作開始筑巢周期的提示，因為在這個時候能保證有足夠的食物來源。

  The adaptive significance at photoperiodism in plants is also clear. Short-day plants that flower in spring in the temperate zone are adapted to maximizing seedling growth during the growing season. Long-day plants are adapted for situations that require fertilization by insects, or a long period of seed ripening. Short-day plants that flower in the autumn in the temperate zone are able to build up food reserves over the growing season and over winter as seeds. Day-neutral plants have an evolutionary advantage when the connection between the favourable period for reproduction and day length is much less certain. For example, desert annuals germinate, flower and seed whenever suitable rainfall occurs, regardless of the day length.

  植物對光周期現(xiàn)象的適應(yīng)性也很明顯。溫帶地區(qū)的短日照植物在春天開花以便在生長季節(jié)讓幼苗長得最快。長日照植物會選擇能夠得到昆蟲授精或者使種子有較長成熟期的時期。溫帶的短日照植物秋季開花，這樣能夠在生長季節(jié)建立食物儲備，也能以種子的形式度過冬天。日中性植物有進化優(yōu)勢。對于它們而言，繁殖的最好季節(jié)和日照長度之間并沒有必然的關(guān)系。例如，對于沙漠的一年生植物而言，只要有合適的雨水，它們就會生長、開花、結(jié)果，不受日照長短的影響。

  The breeding season of some plants can be delayed to extraordinary lengths. Bamboos are perennial grasses that remain in a vegetative state for many years and then suddenly flower, fruit and die (Evans 1976). Every bamboo of the species Chusquea abietifolio on the island of Jamaica flowered, set seed and died during 1884. The next generation of bamboo flowered and died between 1916 and 1918, which suggests a vegetative cycle of about 31 years. The climatic trigger for this flowering cycle is not yet known, but the adaptive significance is clear. The simultaneous production of masses of bamboo seeds (in some cases lying 12 to 15 centimetres deep on the ground) is more than all the seed-eating animals can cope with at the time, so that some seeds escape being eaten and grow up to form the next generation (Evans 1976).

  一些植物的生殖期會拖得特別長。竹子是多年生植物，在很多年的時間里都保持生長狀態(tài)，然后突然開花、結(jié)果、死亡(Evans, 1976)。1884年，牙買加島上的Chusquea abietifolia竹子全部開花、結(jié)果、死亡。下一代的這種竹子在1916年到1918年間也都開花、死亡了，這喑示這種竹子的生長期大約為31年。這種花期循環(huán)的氣候誘因目前還不清楚，但是其適應(yīng)性卻是很清楚的。大量的竹子同時育種(在一些例子中，種子在地下12到15厘米深)，種子的數(shù)量超過了這一時期以種子為食的動物所能吃掉的全部數(shù)量，這樣，一些種子就能存活下來，長成下一代(Evans, 1976)。

  The second reason light is important to organisms is that it is essential for photosynthesis. This is the process by which plants use energy from the sun to convert carbon from soil or water into organic material for growth. The rate of photosynthesis in a plant can be measured by calculating the rate of its uptake of carbon. There is a wide range of photosynthetic responses of plants to variations in light intensity. Some plants reach maximal photosynthesis at one-quarter full sunlight, and others, like sugarcane, never reach a maximum, but continue to increase photosynthesis rate as light intensity rises.

  光對于生物體來說很重要的第二個原因是由于它對光合作用至關(guān)重要。光合作用是植物通過太陽能將土壤或水中的碳轉(zhuǎn)化成供生長所需的有機物質(zhì)的過程。通過計算植物對碳的吸收速率可以計量出光合作用的速率。光合作用對植物的影響因為光照強度的不同有很大的區(qū)別，一些植物在1/4全光照的時候能達到光合作用最高值;而另外一些植物，比如甘蔗，從來不能達到最髙值，但是隨著光照強度的增加，光合作用的速率會持續(xù)增高。

  Plants in general can be divided into two groups: shade-tolerant species and shade-intolerant species. This classification is commonly used in forestry and horticulture. Shade-tolerant plants have lower photosynthetic rates and hence have lower growth rates than those of shade-intolerant species. Plant species become adapted to living in a certain kind of habitat, and in the process evolve a series of characteristics that prevent them from occupying other habitats. Grime (1966) suggests that light may be one of the major components directing these adaptations. For example, eastern hemlock seedlings are shade-tolerant. They can survive in the forest understory under very low light levels because they have a low photosynthetic rate.

  總體而言，植物可以被分為兩種：耐陰類和喜光類。這一分類在林業(yè)和園藝業(yè)中廣泛使用。耐陰植物光合作用的速率低，因此生長速度低于喜光植物。植物物種會逐漸適應(yīng)生活在某一特定的環(huán)境中，并在此過程中產(chǎn)生一系列的特性，這些特性會阻止它們?nèi)フ紦?jù)別的環(huán)境。Grime (1966)指出，光照可能是指導(dǎo)這些適應(yīng)性的主要因素之一。例如，東方的芹葉鉤吻幼苗是耐陰植物，它們可以生存在森林中光照很少的林下葉層，因為它們的光合作用速率低。

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