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Why Desert Plants Store Water in Thick, Waxy Stems
沙漠植物为何将水分储存在厚蜡质茎中
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Desert plants like cacti evolved thick stems to store water during rare rainfalls.仙人掌等沙漠植物演化出粗厚的茎，以在罕见的降雨中储水。
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Their waxy outer layer minimizes evaporation by sealing moisture inside plant tissues.它们蜡质的外层能锁住水分，最大限度减少蒸发。
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Stomata open only at night to absorb CO₂ while reducing daytime water loss.气孔仅在夜间开放，吸收二氧化碳，同时减少白天的水分流失。
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Specialized cells called parenchyma hold large volumes of water without bursting.一类名为薄壁组织的特化细胞能大量储水而不破裂。
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The stem’s ribbed structure expands when hydrated and contracts during droughts.茎部的肋状结构在吸水时扩张，干旱时收缩。
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This adaptation lets them survive months without rainfall in arid environments.这种适应性使它们能在干旱环境中数月无雨仍存活。
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Some species store up to 90% of their mass as water in these modified stems.某些物种在这些特化的茎中储存的水分可达自身体重的90%。
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Unlike leaves, stems perform photosynthesis when leaves are absent or reduced.当叶片缺失或退化时，茎可代替叶片进行光合作用。
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Root systems spread widely but shallowly to capture surface runoff quickly.根系广泛而浅层分布，以便快速吸收地表径流。
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These traits collectively demonstrate how evolution optimizes survival under extreme scarcity.这些特征共同体现了进化如何在极端匮乏条件下优化生存能力。