Tree Physiology Explained and ISA Quiz

Page 3 Root Function Roots anchor the plant, absorb water and mineral nutrients, and provide for food storage. The importance of roots is easily overlooked because they usually are not seen and are difficult to study. Because the roots of a plant are underground, their size and spread is not easily realized. The extent of the root system of a plant can be appreci­ ated from data reported for a rye plant that was found to have 387 miles of root and 2,554 square feet of root surface area. The type of root system a plant develops-the depth, spread, and degree of branching-is an inherited charactelisric, influenced by the type of soil in which the plant is grow­ ing. In heavy and/or wet soils, most of the root system will be near the surface of the soil. However, these roots may spread down to 10 or more feet in light and sandy soil. Many plant roots live in a symbiotic relationship with certain nonpathogenic fungi resulting in mycorrhizal roots. Mycor­ rhizae are fom1ed from both plant and fungus tissues. In symbiosis, both organ­ isms. the plant and fungus, benefit from the bvi ng arrangement. The mycorrhizae, or "fungus roots," derive nourishment from the plant and aid in the absorption of water and essential mineral elements. Water and minerals dissolved m soil water are absorbed by the roots or mycorrhizae and are pumped into the conducting cells of the roots. The energy required for growth of roms and for absorption of mineral salts by roots is obtained by oxidizing sugars in the process of respiration. Therefore, roots require oxygen, which must be available from the air in the soil. In fact, all living cells in a tree require oxygen for respiration. Nitrogen and mher mineral elements are absorbed as ions (charged molecules or atoms) from the soil in water solution by plant roots. TI1e exact nature of ion absorption is unknown, but most evidence indicates that (l) protein carriers cross the membrane, (2) specific binding sites on the membrane attract Ions from soil solution, or (3) perhaps both ex-pla­ nations are valid. The internal concemration of ions is likely to regulate ion absorpuon and may be at least partially under hormonal control. A COLLECTION OF CEU ARTICLES A high concemration of ions in the soil solution may cause plant injury. This higher concentration occurs because of decreases in water porential or unfavorable changes in pH, or because the proporuon of various ions become unbalanced. Decreased water potential of the soil solution is the most likely cause of injury. This so-called "salt effect" reduces water absorption, increases leaf water ddicits, and may lead to injury to tissues from desiccation. More prolonged and severe dehy­ dration causes stomatal closure and interferes with phmosynthesis. Practically all movement of nitrogen and minerals from roots to shoots occurs in the xylem carried by mass !low in the transpira­ Lional stream. There also IS considerable lateral movement of minerals between >..'Ylem and phloem, and recirculation in the phloem plays an important role in mineral nutrition. Roger Funk is vice pre ident and general manager C?f the Davey Institute, the 1-esearrh and development division of the Davey Tree Expert Company in Kent, Ohio. l . Plam physiology is the study of a. how plants function b. hybndizauon processes c. plant and animal interactions d. the anatomy or suucture of plants 2. Respiration occurs in the mitochondria of plant and am mal cell , and involves the a. breakdown of carbohydrates and the release of oxygen b. oxidation of carbohydrates, the producuon of carbon dioXIde and water, and the release of energy c. production of sugar and oxygen using hght energy d. organelles called chloroplasts 3. Water IS absorbed and moves from livmg cell to living cell b)' a process called a. evapotranspiration b. osmos1 . resp1rauon d. transpiration 4. Transpiration is a. a function of the cambium b. not affected by guard cells in the leaf c. the loss of water vapor from a plant d. the movement of water from the root to the leaf through the phloem 5. The veins of the leafs are composed of two types of cells called a. phloem cells and parenchyma cells b. phloem cells and xylem cells c. xylem cells and parenchyma cells d. ray cells and parenchyma cells 6. Which of the following is not true about the stem of a plant? a. 1t contams phloem and xylem tissue b. it 1s the primary location of photosyn­ thesis in most trees c. it serves as a pathway connecting the roots wnh the leaves d. it supports the leaves so that photo­ synthesis can occur 7. Roots perform all of the following except a. absorbing mineral nutrients vnalto plant health b. anchoring the plant and absorbing water c. carrymg out photosynthesis in the winter months d. fonning relationships \vith fungi (called mycorrhizae) 9