【好问题：树木从何而来？树的木质从何而来？】

你知道吗？树木并非仅仅从土壤中生长出来，它们也来自空气中的碳……

这是大自然最不可思议的“魔术”之一：树木本质上是由凝固的稀薄空气构成的。我们往往认为树木会吸收地球的物质，但实际上，树木绝大部分的物理结构——树干、树皮和树枝——都是由直接从大气中吸收的二氧化碳构成的。

通过光合作用，树木利用太阳能从二氧化碳中分离出碳，并将其转化为纤维素纤维，从而赋予木材强度。

相比之下，土壤更像是多种维生素，而非主要的食物来源。虽然树根对于固定树木和吸收水分至关重要，但它们吸收的矿物质（如氮和磷）仅占树木干重的约5%。森林的“主体”实际上是由地球的呼吸构成的，这使得树木成为终极的碳捕获技术。

这种循环在生与死的层面上也呈现出一种优美的对称性。当一棵树被烧毁或腐烂时，它并不会就此消失；它会将储存的碳以气体的形式释放回空气中。有趣的是，人类也参与着一个类似的逆向过程——当我们减肥时，我们并非只是把脂肪“燃烧”掉；实际上，我们还会将这些脂肪以二氧化碳的形式呼出体外。从某种意义上说，我们今天呼出的碳，明天就可能变成一棵幼苗的木材。

Where does a tree come from?
Where does a tree's mass come from?

Did you know trees don’t really just grow from the ground, they also come from the carbon in the air…

It is one of nature’s most incredible "magic tricks": trees are essentially solidified thin air. While we tend to think of them as sucking mass out of the earth, the vast majority of a tree’s physical structure—its trunk, bark, and branches—is built from carbon dioxide pulled directly from the atmosphere.

Through photosynthesis, trees use solar energy to strip the carbon from CO2 and transform it into the cellulose fibers that give wood its strength.

The soil, by contrast, acts more like a multivitamin than a primary food source. While the roots are essential for anchoring the tree and absorbing water, the minerals they extract (like nitrogen and phosphorus) account for only about 5% of the tree's total dry mass. The "bulk" of the forest is quite literally constructed from the breath of the planet, making trees the ultimate carbon-capture technology.

This cycle is also beautifully symmetrical when it comes to life and death. When a tree is burned or decays, it doesn't just disappear; it releases that stored carbon back into the air as gas. Interestingly, humans participate in a similar process in reverse—when we lose weight, we aren't just "burning" fat away into nothingness; we are actually exhaling that mass as carbon dioxide. In a very literal sense, the carbon we breathe out today could become the wood of a sapling tomorrow.

Via Steve Mould http://t.cn/AXqjocve