♻️ 碳循环：碳原子的环球旅行♻️ Carbon Cycle: A Carbon Atom's World Tour
上一片护森林，这一片跟一颗小碳去旅行：它从森林出发，最后还能回家吗？Last leaf guarded the forest. Now follow one little carbon atom from that forest — can it ever come home?
第 1 步：四站大循环Step 1: Four stops, one big loop
先看全程：小碳只走四站，却能无限循环。The whole trip first: little Carbon visits just four stops, looping forever.
大气里的二氧化碳，被植物光合固定；动物吃了植物，碳进身体；呼吸和燃烧又把它放回大气；落叶残体进土壤，分解也会释放。转完一圈，再来一圈。CO2 in the air is fixed by plant photosynthesis; animals eat plants and take carbon in; breathing and burning send it back to the air; fallen leaves reach soil, and decay releases it too. Loop after loop.
循环转得好好的，谁把它打破了？The loop ran fine — who broke it?
第 2 步：天平被压歪了Step 2: The balance tips over
人类多烧化石燃料，等于往天平左边狂加码；又砍森林，右边吸碳的砝码变轻。天平歪了，大气里的碳越堆越多。Burning extra fossil fuels piles weights on the release side; cutting forests lifts weights off the absorb side. The balance tips — carbon piles up in the air.
天平歪了，怎么把它摆平？How do we level the balance again?
第 3 步：摆平天平的两招Step 3: Two moves to level it
碳中和就是让排放等于吸收，天平重新摆平。森林是最大碳银行：光合吸碳，树干木材把碳存住。保住森林，少烧化石，小碳就能回家。Net zero means release equals absorb — the balance levels again. Forests are the biggest carbon bank: leaves take carbon in, trunks and timber store it up. Keep forests, burn less, and little Carbon gets home.
🎮 你就是小碳（30 秒）🎮 You are little Carbon (30 seconds)
故事讲完了。替小碳选对每一程的下一站，走满 4 站回到大气。Story done. Pick the right next stop for little Carbon, all 4 legs home to the air.
一句话记住它：碳在大气生物土壤间循环：光合固定，呼吸燃烧释放；人类多放少吸打破平衡，碳中和加森林能修好。Remember it in one line: carbon loops through air, life and soil — photosynthesis fixes it, breathing and burning release it; extra release breaks the loop, net zero plus forests fix it.
闭环四站：大气 → 植物 → 动物 → 土壤 → 大气Four stops, one loop: air → plant → animal → soil → air人类打破：多烧化石多排放，砍森林少吸收Humans break it: more burning releases more, fewer forests absorb less修法：碳中和摆平天平，森林碳汇吸碳存碳The fix: net zero levels the balance; forest banks take in and store carbon
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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