Yes! And it’s a very important question: all citrus trees are grafted (grafting is a method of asexual plant propagation where the tissues of one plant are fused with another plant).
Above the graft is good, viable foliage. However, if stems, suckers and foliage begin to grow from the grafted portion (bottom of citrus tree) the tree will produce sour citrus if not pruned or cut off. You must prune growth from grafted area to avoid souring fruit. Trim as desired or needed preferably in the warmer months. (Read more on how to prune your citrus tree here)