十万个为什么·科学阅读30篇（4）

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为什么某些地衣只生长在酸性岩石表面？

Lichens are symbiotic organisms made of fungi and algae or cyanobacteria.
They survive in extreme environments where few other plants can grow.
Some lichen species produce acids that slowly dissolve rock minerals to extract nutrients.
Acidic rocks like granite contain minerals such as quartz and feldspar that resist weathering.
These lichens thrive there because their acid secretion matches the rock’s low pH buffer capacity.
On alkaline limestone, the same acids react too strongly and inhibit growth.
Scientists measure lichen distribution to monitor long-term air quality and rock weathering rates.
Their slow growth—often less than one millimeter per year—makes them excellent environmental recorders.
Because they absorb everything from the air, they accumulate pollutants like heavy metals over decades.
This makes them natural bioindicators for ecological change across centuries.