How would a volcanic eruption affect photosynthesis in 100 years

It si saud that volcanic soil is very rich for vegetation to grow as soon the soil is cool of, so in short term they are very beneficial. Now in a hundred year period, plants like the photosynthetic plankton are affected in a good sense because ashes can cause a large bloom of these kind of species. These helps us to conclude that volcanic plumes can fertilized also oceans and preserve plants like planton. some researchers have found that this could fight global warming by spurring the growth of marine plants that can suck carbon dioxide from the air.