In a self-sustaining ecosystem which component cannot be recycled

Ecology is the branch of biology which deals with the interactions between organisms and their environment. To be able to extensively study ecology, there are different levels of organizations to be considered and one of which is ecosystem.

The ecosystem consists of a living community and non-living environment that functions together. It is capable of supporting itself and is constant when these three conditions are met:  ENERGY, AUTOTROPHS and RECYCLING.

The answer to the above question would be ENERGY; because in order for an ecosystem to thrive, it must have a continuous flow of energy and at the same time be able to recycle materials.