The three handsome soldiers in this photograph are all wearing the WWI Imperial Belt Plate of Czarist Russia. There is nothing on Russian military uniforms in my local library, so I can't tell you anything about the units to which they belonged. Perhaps the key to that information is on the back of the photograph in the text written in pencil, which I believe also gives the soldiers' names. Hopefully someone will be able to translate it.
It is of interest to note that after the Russian Revolution broke out during the latter part of WWI, many soldiers on the side of the Revolutionists kept their belt plates and continued to wear them, but sanded off or otherwise obliterated the Russian Imperial Eagle.
WWI Russian Army