Why do spots appear on iceburg lettuce during cold storage？（0~4℃） Why does round lettuce appear spot during cold storage？（0~4℃）Is it still edible?

I would like to extend the storage time.

Lettuce is packaged with other vegetables, like red chicory, NewZealandspinach, Romaine Lettuce, etc.

May be my expression is not clear, my English is very poor, please forgive me. I want to know the reason of the spotting, so I can avoid it.
The brown spots you see are known as "russet spotting". This is a reaction which is believed to be caused by ethelyne gas emitted from citrus, such as apples, bananas, etc.

Bottom line, the lettuce is completely safe to eat. It's certainly less visually appealing, but it is indeed safe to eat. For ideas on preventing russet spotting, check out the source linked above.