It's not necessarily leading to the overgrowth. Nitrogen fixation is a really expensive process. It means you will need to spend a lot of energy on this process

It's not necessarily leading to the overgrowth. Nitrogen fixation is a really expensive process. It means you will need to spend a lot of energy on this process. The nature is a self balanced eco system. Species need to have certain amount of growth speed to keep itself competitive. A species that growth much slower but not require extra supplement is not necessary going to win the original one if it just get wipe out of the ecosystem.