photosynthetic
Magnesium Mg and calcium Ca are also important macronutrients. The role of calcium is twofold: to regulate nutrient transport, and to support many enzyme functions. Magnesium is important to the photosynthetic process. These minerals, along with the micronutrients, which are described below, also contribute to the plants ionic balance. In addition to macronutrients, organisms require various elements in small amounts. These micronutrients, or trace elements, are present in very small quantities. They include boron B , chlorine Cl , manganese Mn , iron Fe , zinc Zn , copper Cu , molybdenum Mo , nickel Ni , silicon Si , and sodium Na . Deficiencies in any of these nutrientsparticularly the macronutrientscan adversely affect plant growth Figure 31.4. Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis yellowing of the leaves . Extreme deficiencies may result in leaves showing signs of cell death.