Which group of plants would be the first colonizers in an ecological succession changing rocks to soil?

Lichens would be the first colonizers in an ecological succession changing rocks to soil. Lichens are symbiotic organisms that consist of a fungus and an alga or cyanobacterium. They are able to grow on bare rocks and start breaking them down into soil by secreting acids that dissolve the rock surface. The breakdown of rocks and the accumulation of organic matter in the lichen thalli contribute to the formation of soil. This process is the first step in ecological succession, where plants and other organisms gradually colonize a barren area and change its ecological community over time.