What would happen to the atmosphere if no plants?

If there were no plants, the atmosphere would undergo significant changes. Without photosynthesis, which plants use to convert carbon dioxide into oxygen, levels of carbon dioxide would rise while oxygen levels would decline. This would lead to increased greenhouse gas effects, contributing to climate change, and could result in a less breathable environment for most aerobic organisms. Ultimately, the absence of plants would disrupt ecosystems and diminish biodiversity.