In which of the following processes do decomposers play a vital role?

Decomposers are essential to the process of nutrient cycling, which involves the breakdown of organic matter and the recycling of nutrients back into the ecosystem. Decomposers, such as fungi and bacteria, break down dead plants, animals, and waste products, converting them into simpler substances. This process releases essential nutrients like nitrogen, phosphorus, and carbon, making them available for uptake by plants and other organisms.

In contrast, photosynthesis is primarily the process by which plants convert sunlight into chemical energy, cellular respiration is a metabolic process used by organisms to convert sugars into energy, and energy production generally refers to various ways organisms generate energy for their biological functions. While these processes are all crucial for the functioning of ecosystems, they do not specifically rely on decomposers in the same integral way that nutrient cycling does.