Photosynthesis & Oxygen Production (Daytime) Most trees and plants produce oxygen during the day through photosynthesis, which requires sunlight. They absorb carbon dioxide (CO) and release oxygen (O). What Happens at Night? Effluent Treatment Plant (ETP) Where, why and how does Ecosia plant trees? Capillary Action Technique Planting pots of different sizes and shapes with holes at the bottom are used. Fill these pots with an inert medium and plant seedlings seeds in that inert medium. :