本篇文章共分 3 段，討論植物對溫度的適應方式，主要內容針對高山地區的針葉木以及沙漠地區的仙人掌這兩類極易遭遇嚴寒溫度的植物，分別說明其獨特的適應方式。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

Plant Adaptations to Cool Environments 植物對涼爽環境的適應性

1. 植物對溫度的適應

   There are many interesting adaptations that allow plants to survive in cool environments. One obvious strategy is dormancy (a suspension of activity) during the cold season, Most of the common trees in the forests of northeastern North America, western Europe, and eastern Asia, such as the maples, oaks, beech, birches, and ashes, are deciduous trees that lose their frost-sensitive leaves during the cold winter season. In most of these trees, the leaves suffer damage at temperatures of freezing or just below. The new leaves arise in the spring from winter buds that can remain viable at colder temperatures

   有許多有趣的適應方法使植物能夠在涼爽的環境中生存。一項明顯的策略是在寒冷季節進行休眠（暫停活動）。北美東北部、西歐和亞洲東部森林中的大多數常見樹木，如楓樹、橡樹、山毛櫸、樺樹和白楊木，都是落葉樹，在寒冷的冬季會脫落對霜凍敏感的葉片。在這些樹中，大多數樹的葉子在冰點或略低於冰點的溫度下會遭受損傷。春天，新葉會從在較低溫度下能保持活力的冬芽中長出。

2. 針葉木的溫度適應方式

   Most of the needle-leaved conifers of the northern and alpine forests, such as pines, spruces, and firs, do not lose their leaves during the winter. How do such evergreen plants escape intracellular freezing (freezing within cells) and tissue destruction when temperatures may drop to -40° C or colder? In these plants, the onset of cool temperatures causes physiological changes that allow plant tissue to either avoid freezing or restrict freezing to extracellular areas (those outside of cells). For plants to avoid freezing, they must chemically alter their liquids into a form that is analogous to antifreeze in automobiles. The liquids in these plants can be cooled far below 0° C and will not freeze. This process is called supercooling and is achieved by the metabolic synthesis of sugars and other molecules which, when in solution in the plant’s tissue, lower the temperature for ice formation to far below 0° C. Supercooling seems to be the prevalent mechanism of frost resistance in herbs. For woody plants, supercooling is augmented by declines of cellular water content, greater cellular accommodation to deformation, and processes that allow water to accumulate and freeze in extracellular spaces. The loss of water from the cells to extracellular areas increases the solute content (the quantity of dissolved substances) of the remaining cell water, making it more resistant to freezing. The cell walls can accommodate the deformations caused by water freezing on the exterior of the cell. For northern and alpine evergreens such as pines and spruces, both supercooling and extracellular ice formation play a part in allowing the plants to withstand extremely cold temperatures. One interesting facet of these physiological adaptations to freezing is that most of these plants will still be damaged by cold temperatures if they do not have a period of cooling in which to adjust to the onset of winter. This process of physiological preparation for the onset of winter cold is called frost hardening.

   北方和高山森林的大多數針葉植物，如松樹、雲杉和冷杉，在冬季不會掉葉子。當溫度可能下降到攝氏零下 40 度或更低時，這種常綠植物如何逃避細胞內凍結（細胞內凍結）和組織破壞？在這些植物中，低溫的到來會引起生理變化，使植物組織避免凍結或將凍結限制在細胞外區域（細胞外的區域）。為了避免凍結，植物必須用化學方法將其液體改變成類似於汽車防凍劑的形式。這些植物中的液體可以被冷卻到遠低於 0°C 的溫度而不會凍結。這個過程稱為過冷，是通過糖和其他分子的代謝合成實現的，這些分子在植物組織的溶液中時，可將形成冰的溫度降低到遠低於 0°C。過冷作用似乎是草本植物抗凍的普遍機制。對於木本植物，過冷作用因細胞含水量下降、細胞對變形的適應性更強以及允許水在細胞外空間積聚和凍結的過程而得到加強。水從細胞中流失到細胞外區域，增加了剩餘細胞水的溶質含量（溶解物質的含量），使其更耐凍。細胞壁可以適應水在細胞外部凍結造成的變形。對於北方和高山常綠植物，如松樹和雲杉，過冷和細胞外冰的形成在使植物能夠承受極度寒冷的溫度方面發揮了作用。這些對冰凍的生理適應性有趣的一點是，如果這些植物沒有一個冷卻期來適應冬季的到來，它們中的大多數仍然會被低溫所破壞。這種為冬季開始的寒冷做生理準備的過程被稱為霜凍硬化。

3. 仙人掌的溫度適應方式

   Some members of the cactus family appear to resist freezing during cool nights by radiating heat stored during the day in their thick, moist tissue. The greater the mass of the cactus, the more heat it can store and the less prone it will be to freezing damage during the night. How is it then that these cacti can survive cold temperatures when they are young and small? The giant saguaro cactus is perhaps the best-known symbol of the southwestern desert of North America. In the popular lore of North America, the distinctive shape of the multi-stemmed saguaro is a universally recognized icon that is used to represent deserts in movies, television, and comics. Yet, this distinctive and widely recognized plant is actually found only in the Sonoran Desert of California, Arizona, and adjacent Mexico. The saguaro cactus is damaged or killed if exposed to prolonged freezing temperatures. Desert climates in the northern Sonoran Desert are typified by warm days but sometimes experience nighttime temperatures that are below freezing in the winter. Young saguaros that survive are found sheltered beneath more frost-tolerant desert shrubs. The cover of these shrubs acts as a thermal blanket, capturing heat radiated from the ground and keeping the microclimate of the small saguaro warm at night. As the cactus grows, it eventually rises above the cover of the protective shrub. The radiation of heat from the stalk of the large mature cactus prevents freezing. This strategy works up to a point. The range of the saguaro is restricted to areas that do not experience more than about 12 to 24 continuous hours of air temperatures below 0° C. It appears that after 24 hours of freezing air temperatures, not enough heat reserve is left in the saguaro to keep the tissue from freezing.

   仙人掌家族的一些成員似乎可以在涼爽的夜晚通過散發白天儲存在其厚實、濕潤組織中的熱量來抵禦冰凍。仙人掌的質量越大，它能儲存的熱量就越多，在夜間就越不容易被凍壞。那麼，為什麼這些仙人掌在年輕和小的時候可以在低溫下生存呢？巨大的沙瓜羅仙人掌也許是北美西南沙漠最知名的象徵。在北美的流行傳說中，多莖沙瓜羅的獨特形狀是一個普遍認可的標誌，在電影、電視和漫畫中被用來代表沙漠。然而，這種獨特的、被廣泛認可的植物實際上只存在於加利福尼亞州的索諾蘭沙漠、亞利桑那州和鄰近的墨西哥。沙瓜羅仙人掌如果暴露在長期的冰凍溫度下，就會受到損害或死亡。索諾蘭沙漠北部的沙漠氣候以溫暖的白天為特徵，但有時冬季的夜間溫度會低於冰點。存活下來的年輕沙瓜羅被發現躲在更耐凍的沙漠灌木下面。這些灌木的覆蓋起到了熱毯的作用，可以捕捉地面輻射的熱量，使小沙瓜羅周邊的微氣候在夜間保持溫暖。隨著仙人掌的生長，它最終會升到保護性灌木的覆蓋物之上。大型成熟仙人掌的莖部輻射的熱量可以防止凍結。這種策略在一定程度上是有效的。仙人掌的分佈範圍被限制在空氣溫度連續低於 0°C 的時間不超過 12 至 24 小時的地區。看起來，空氣溫度凍結 24 小時後，仙人掌中沒有足夠的熱量儲備來保持組織不被凍結。