Yes. Plants grow on Pandora, its quite obvious in the movie. The high concentration of carbon dioxide in the Pandoran atmosphere makes it extremely poisonous to humans and will kill them in about 4 minutes.
Actually, the atmosphere of Pandora consists of other toxins beyond carbon dioxide, some of which are rather corrosive. No only can one not survive long breathing it, according to a product affiliated site employees were recommended to avoid spending more than 20 minutes a day exposed to the atmosphere.