Pressing for greener environment Kalam asked children to plant more trees. “I would also ask children to plant at least five trees and nurture till they get matured. Every young person has to take oath to plant at least five trees and nurture them,” he said. “A matured tree can absorb about 20 kg of carbon dioxide (CO2) in a year. At the same time it releases around 14 kg of oxygen (O2) in the atmosphere, Save tree save nature.