what are the effects if there is a reduction or decrease of photosynthesis in the ecosystem

It would be similar, but not as extreme as indicated below.

It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time Earth’s atmosphere would become nearly devoid of gaseous oxygen.

Did you know?

Did you know that a reduction or decrease in photosynthesis can have significant effects on an ecosystem? Photosynthesis, the process by which plants and other organisms convert sunlight into energy, plays a crucial role in maintaining the balance of oxygen and carbon dioxide in the atmosphere. It also serves as the foundation of most food chains, as plants are the primary producers that provide energy to other organisms through their tissues. If photosynthesis is reduced, it can lead to a decline in oxygen production, a rise in carbon dioxide levels, and a disruption in the food chain. This can have far-reaching consequences, impacting the survival and distribution of various species and ultimately affecting the overall health and stability of the ecosystem.