* Carbon dioxide (CO2): This is the primary substance trees take in from the air for photosynthesis. They use it to create sugars for energy and growth.

* Oxygen (O2): While trees release oxygen as a byproduct of photosynthesis, they also need a small amount of oxygen for respiration, which is how they break down sugars to fuel their cells.

* Nitrogen (N2): This is a crucial nutrient for tree growth. While trees can't directly absorb nitrogen gas from the air, they rely on nitrogen-fixing bacteria in the soil to convert it into a usable form.

* Other gases: Trace amounts of other gases, like ozone and sulfur dioxide, can be taken in by trees. These gases can have negative impacts on tree health and can be pollutants.

It's important to note that trees absorb these substances through tiny pores called stomata on their leaves. These pores open and close to regulate the intake of gases and water vapor.