Is it permissible in Islamic law, and would it affect the laws of inheritance, for a husband to gift a portion of land he owns to his wife in appreciation of her efforts, knowing that he has children from her and from another wife?

What a man bestows upon his wife while he is healthy is legally permissible, and the gift is completed by the wife taking possession of it. This does not affect her inheritance. However, scholars have differed on the permissibility of a man bestowing a gift upon one of his wives to the exclusion of the others.