The most noticeable plant-life in the world is the "tree". The tree comes in many different types, so many that "tree" is considered a description rather than a species. The tree is a plant which relies on its roots to get nourishment. The tree can grow as large or as small as necessary: as long as its roots can reach sufficient water and nutrients, the tree can continue growing.
As soon as it reaches the point where all available nutrients are being used to maintain the current size, it stops growing. If the amount of nutrients available decreases, then the tree will stop providing nourishment to one of its branches, and if the amount of nutrients doesn't return to normal or increase, that branch will fall off. If the nutrients continue to decrease, more and more branches will die, and eventually the trunk itself.