This is talking about spiritual death or separation from God. All physically die whether they believe in Christ or not. He died in our place so we can be in His presence. Plant cells are very similar to animal cells (with a few small differences) so it would be strange to suggest that animal death is the result of corruption from sin, but plant death is not. While plants are not considered ‘nephesh’, both humans and animals are. Animals do not need to be saved from the wages of sin, but humans who are being made in God’s image, made spiritually alive do.
- Rom 6:23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
So it can’t be physical death that entered the world through Adam. Adam did not “surely die” but was spiritually separated from God and sent out of the Garden which represents God’s presence.
But Paul does not specifically say that Adam was historic or a literal person. That is your belief, and would be Paul’s as well, but Paul does not specifically claim that because it is not pertinent to the faith. Paul instead describes Adam as a ‘figure’ and his sin as a ‘similitude’. So Adam represents all humanity and his sin represents all sin.