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Why Do Certain Cacti Bloom Only Once Every Several Years?
为什么某些仙人掌要隔好几年才开花一次？
精读先不看文字，完整听一遍。
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Some desert cacti, like the saguaro, store energy for years before producing their first flowers.一些沙漠仙人掌（如巨人柱）会储存能量多年，才开出第一朵花。
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Flowering demands huge resources, so plants wait until they have enough stored water and nutrients.开花需要大量资源，因此植物会等到蓄积了足够的水分和养分后才开花。
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Long intervals reduce competition among offspring and increase survival chances during rare rainy years.漫长的开花间隔可减少后代间的竞争，并提高在罕见雨季中的存活率。
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Genetic timing mechanisms interact with environmental cues such as nighttime temperature drops and rainfall patterns.遗传计时机制与夜间降温、降雨模式等环境信号相互作用。
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Scientists found that epigenetic switches—chemical tags on DNA—help regulate this multi-year blooming cycle.科学家发现，DNA上的化学标记（表观遗传开关）有助于调控这种跨年开花周期。
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Each bloom may last only one night, attracting specialized bats or moths adapted to desert pollination.每朵花可能仅开放一晚，吸引适应沙漠授粉的特化蝙蝠或蛾类。
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Drought stress can delay flowering further, while unusually wet seasons sometimes trigger unexpected blooms.干旱胁迫可能进一步推迟开花，而异常湿润的季节有时会触发意外开花。
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This strategy evolved because deserts offer unpredictable water, making frequent reproduction too risky.这种策略是在沙漠水资源不可预测的环境中演化而成的，频繁繁殖风险过高。
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Even mature cacti may skip years if conditions fail to meet strict physiological thresholds.即使已成熟的仙人掌，若条件未达到严格的生理阈值，也可能多年不开花。
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Studying these rhythms helps predict how climate change might disrupt fragile desert plant-animal relationships.研究这些节律有助于预测气候变化如何破坏脆弱的沙漠动植物关系。
精读 · 大约 10 分钟
听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。
③ 学 · 重点表达
- Scientists found that epigenetic switches—chemical tags on DNA—help regulate this multi-year blooming cycle. 科学家发现，DNA上的化学标记（表观遗传开关）有助于调控这种跨年开花周期。
- This strategy evolved because deserts offer unpredictable water, making frequent reproduction too risky. 这种策略是在沙漠水资源不可预测的环境中演化而成的，频繁繁殖风险过高。
- Long intervals reduce competition among offspring and increase survival chances during rare rainy years. 漫长的开花间隔可减少后代间的竞争，并提高在罕见雨季中的存活率。
④ 懂 · 选一选
⑤ 今天会说这一句
Scientists found that epigenetic switches—chemical tags on DNA—help regulate this multi-year blooming cycle.
⑥ 跟读并录音
Scientists found that epigenetic switches—chemical tags on DNA—help regulate this multi-year blooming cycle.
第一版：录下来、回听、再听标准音。系统打分以后再加。
⑦ 说 · 自己来一句
用今天的表达，自己说一句。
例子：Scientists found that epigenetic switches—chemical tags on DNA—help regulate this multi-year blooming cycle.
已记下。连续天数以后会显示在课表里。
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