What Is a Brownfield Project? Environmental Works, Inc. Geum 'Lady Stratheden' 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? If your ZZ isn't standing tall, it might just be feeling a little cramped When roots run out of room, new growth slows down and the branches can start to droop.