Your sentence is almost correct but needs a few small improvements for grammar and clarity. Here's a better way to say it:
Original: Mangrove trees get rid of extra salt by storing it in leaves and dropping them.
Corrected: Mangrove trees get rid of extra salt by storing it in their leaves and dropping the leaves.
Explanation:
- We add their to show that the leaves belong to the mangrove trees.
- It's clearer to say dropping the leaves instead of just dropping them, so it's easier to understand what is being dropped.
This makes the sentence clear and easy to understand.