ABSTRACT
I. INTRODUCTION Plant growth is balanced between growth above ground (shoot growth) and below ground (root growth). This balance provides adequate surface area to intercept light for photosynthesis as well as sufficient area to acquire needed water and nutrients in the soil. In this way, the requirements for carbon (C) and mineral nutrients such as nitrogen (N) within the plant are satisfied to maximize plant growth or productivity. Each plant species appears to have a preferred balance, which is apparently genetically controlled but which can be altered by environmental conditions. For example, if a needed resource such as water or a nutrient is limiting, a plant often tends to grow a proportionally greater amount of root [1,2]. This gives the plant more surface area within the soil to absorb the limited supply of resources and also to search out pockets of resources deeper within the soil. In a similar sense, if the shoot is exposed to a limit in a resource (most commonly light, which is necessary to acquire C through photosynthesis), growth will shift to favor shoot growth over root growth. This supplies the plant with greater surface area to intercept light and absorb carbon dioxide and brings balance back to the plant.
