   Plant Mineral Nutrition, Part 1 - December 2, 1998 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Plants are autotrophic organisms. In other words, They make their own food. Humans (and other animals) are heterotrophs. We must extract energy from plants or other organisms that ultimately extracted their energy from plants. As it stands, humans may be fairly smart, but not quite smart enough to make their own food. Plants need a suitable environment to make their living. Sun, water, oxygen and carbon dioxide are needed for photosynthesis (Backyard Gardener August 7, 1998), but plants need an infrastructure before they go into the business of sugar production. To build this infrastructure, plants extract additional raw materials from the soil. In total, there are seventeen elements currently believed essential to all higher plants. These essential nutrients are commonly divided into two groups: macronutrients (those found in relatively high quantities in plant tissue) and micronutrients or trace elements (those found in relatively low quantities in plant tissue). Each has one or more specific functions within the plant and normal plant growth and reproduction will not occur without these nutrients. Each will be briefly discussed progressing from those most abundant to those least abundant within plant tissue. Hydrogen is the most abundant nutrient in plant tissue (total atoms not absolute amount by weight). Plants get hydrogen by removing it from water molecules. Most of us know that water consists of two atoms of hydrogen and one atom of oxygen. In addition, we are taught that plants restore oxygen to the atmosphere. Once the two hydrogen atoms are removed from water, oxygen is merely a by-product of the process. Hydrogen is needed by plants for photosynthesis, energy transfers, and many other processes within plants. Carbon enters the plant as carbon dioxide from the atmosphere. The entire purpose of photosynthesis is to get carbon incorporated into organic molecules. Once incorporated, carbon is the "backbone" of all the cellular products. These include sugars, proteins, lipids (fats), and nucleic acids (including DNA). Oxygen is provided by either water or elemental oxygen (O2). All organisms that conduct aerobic respiration need it. Aerobic respiration is a means by which organisms can very efficiently utilize stored energy to create readily usable energy. Just because plants can create and store chemical energy from photosynthesis this does not mean that they get a free ride the rest of the time. All living cells need energy to continue life. Nitrogen can be taken up by plants in two forms: ammonium or nitrate. Both are found in soils, but nitrate is more common. Plants first store nitrogen as amino acids then form proteins by liking amino acids together. When other organisms eat plant material, they digest the proteins and break them back into amino acids. The amino acids then become building blocks for the organism that consumed them. This overly simplified view does not even begin to delve into the overall importance of nitrogen to plant growth. Proteins function as enzymes that catalyze cellular reactions, hormones that convey messages to other cells, and structural support of cells. Nitrogen is also part of several other compounds in plants: DNA, RNA, alkaloids, etc. Nitrogen is readily transported from one place to another within plants. The deficiency symptoms are yellowing older leaves and slow growth rate. Excess nitrogen results in poorly developed root systems, abundant leaves, and retarded flower, fruit and seed formation. Potassium is an activator of plant enzymes essential to photosynthesis, respiration, starch and protein formation, and for the maintenance of turgor pressure in plant cells. It is taken up in its ionic form (K+) and is also highly mobile within the plant. In Arizona, potassium deficiency is uncommon, but it can be recognized by necrotic lesions (dead or dying spots) on leaves of dicots (broad-leafed plants). In grasses, the stalks become weak and roots become easily infected by rot organisms. Calcium is also absorbed in its ionic form (Ca++) and is readily available throughout much of Arizona. Limestone, a common rock type in the Verde Valley, is calcium carbonate: a ready source of calcium. It is important in securing adjacent cells to each other and proper membrane function. The calcium rich, glue-like material between the cells is called the middle lamella. Once in the plant, calcium is highly immobile. Consequently, calcium deficiency is most pronounced at the tips or growth points of the plant. Twisted and deformed tissue can result and can cause blossom end rot in tomatoes. If this column wasn't too technical for you, watch for next week=s Backyard Gardener for Part 2 of this exciting plant nutrition chronicle. If it was too technical, you can do one of three things: (1) take a basic biology class that will increase your technical background, (2) find a pleasant chore (i.e., washing the ceilings) to replace the time you would have spent reading this article, or (3) ask me to lighten it up and write about bedding plants and the wonders of Vitamin B1. The University of Arizona Cooperative Extension has publications and information on gardening and plant science. If you have other questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |