Lemon tree sapling leaves curling up + black spot on branch

[dx4]

As shown in the uploaded image my lemon tree sapling started curling its leaves up and one of them (on the right) is turning brown.

Also a black spot appeared in the lower branch section, near the soil.

Is this normal or is it indicating that my sapling has a health issue?

I water it when the soil becomes dry and I put it in a sunny area during the day and inside during the night. I also protect it from rough winds since its size is too small.

 

[Chuck]

As shown in the uploaded image my lemon tree sapling started curling its leaves up and one of them (on the right) is turning brown.

Also a black spot appeared in the lower branch section, near the soil.

Is this normal or is it indicating that my sapling has a health issue?

I water it when the soil becomes dry and I put it in a sunny area during the day and inside during the night. I also protect it from rough winds since its size is too small.

View attachment 42082

You are keeping the soil too wet. It should be DAMP not wet as shown. The black on the stem is stem rot. I doubt the seedling will survive.