每日吃瓜

Hi everyone,

I'm new to caring for bonsais. I received a Chinese Elm bonsai last year. Noticed that some of the leaves turned yellow and brown. Trying to prune it and noticed that one of the roots is discolored. Scratched the surface of it and it doesn't appear to have any green skin underneath...

I've attached a picture. What do you think it is? Is it root rot? How do I go about caring for the tree now?

Any help or guidance would be appreciated. Just want my tree to be okay! Thanks.