Ecosystem
Producers are beings that produce their own food (like plants through photosynthesis). Therefore, they are the base of the food chain and it is the place where there is the greatest amount of energy.
Decomposers are beings responsible for decomposing organic matter, we can mention as decomposers some fungi and bacteria. They are responsible for returning the nutrients that were in the living being to the environment.
What happens if the producers were removed from an ecosystem?
If the producers are removed from the ecosystem, that ecosystem would not survive for long, as all the energy in the food chain comes from the producers.
Primary consumers would have no food and would die, secondary consumers would have no food and would die... This series would affect all trophic levels.
What happens if the decomposers were removed from an ecosystem?
If the decomposers were removed from the ecosystem, the nutrients would be "trapped" in the organisms and not be returned to the environment. In this way, there will be no recycling of nutrients and these nutrients would start to be lacking for living organisms, leading them to death.