Question

Legumes, a type of plant, require Rhizobia, a type of soil bacteria, to survive since these organisms fix nitrogen during photosynthesis. Rhizobia use the legumes for food. What would most likely happen to the legume population if Rhizobia suddenly became extinct?

Answer 1

They would most likely also become extinct, since they require them to "Fix the nitrogen" during photosynthesis, they have a "You need me, I need you" kind of thing. One can't live without the other.

Answer 2

Answer: The legume population will decrease.

Explanation: Legumes are the plants that use Rhizobia, a bacteria that is used  for nitrogen fixation.

The legumes will not survive and slowly its population will decrease. This is because there will be no nitrogen fixation in the legumes without rhizobia.

Nitrogen synthesis is important for the various metabolic activities inside the plant. So, many processes of the plant will be disturbed and ultimately the plant will die.