My 1 meter Bonsai

Can't really see by the photo.
Compacted soil?
Needle cast disease? (rife where I live)- symptoms are pale needles, turning yellow also at this stage easy to see tiny pustules along the needles. Then needles turn brown and die.
Caused by fungal growth.
Spread by raindrops hitting infected needles and infected splash landing on uninfected needles or needles dropping and infecting the surrounding soil.
URGENT. remove all dead needles from the tree and surrounding soil and burn them to stop/slow infection.
Keep top or soil needle free.
There is a spray you can get to treat this disease. you will need to do some research. Not sure, but I think it was a copper spray.
Personally I don't use any spray. I check for needle cast, pick off ALL infected needles, keep the soil needle free, destroy all dead needles and hope my trees survive.
I've been growing bonsai since 1990, only lost one to needle cast. I lost one Pine due to water-logged compacted soil and another due to bad root pruning. I didn't understand about root pruning medium sized Pines. Guess I learned the hard way.