The study looked at how different levels of salt stress affect the growth, photosynthesis, and root structure of three types of hazelnut seedlings. They found that as salt stress increased, the seedlings' growth decreased, but their root-shoot ratio increased. The photosynthetic rate dropped significantly under moderate and severe salt stress. The seedlings' water use efficiency peaked under mild salt stress. Overall, one of the hazelnut varieties showed better growth and photosynthetic adaptability to salt stress compared to the others.