Nutrition and Transport in Plants Chapter 26 Outline Essential Inorganic Nutrients Soil Formation Soil Profiles Soil Erosion Mineral Uptake Transport Mechanisms Water Organic Nutrients 1 2 Plant Nutrition and Soil Essential Inorganic Nutrients About 95% of a plant s dry weight is carbon, hydrogen, and oxygen.! Carbon dioxide and water Essential nutrients have identifiable role, and a deficiency causes a plant to die.! Macronutrients! Micronutrients Table 26.1 3 4
Overview of Plant Nutrition 5 Fig. 26.2 6 Nutritional Function of Soil Soil is defined as a mixture of soil particles, decaying organic material, living organisms, air, and water. Roots take up oxygen from air spaces. Soil Particles Sand Clay Silt Absorbing Minerals 7 8
Soil Profiles Soil profile is a vertical section from ground surface to unaltered rock below. Parallel layers - Horizons.! A (topsoil) - Litter and humus.! B (subsoil) - Inorganic nutrients.! C (weathered rock) Because parent material and climate differ, soil profile varies according to particular ecosystem. 9 10 Generalized Soil Profile Soil Erosion Soil erosion occurs when water or wind carry soil away to a new location. Worldwide, removes about 25 billion tons of topsoil annually.! Deforestation! Desertification! Agricultural contaminants 11 12
Adaptation of Roots for Mineral Uptake Fig. 26.5 Symbiotic Relationships Rhizobium bacteria fix atmospheric nitrogen.! Live in root nodules. Mycorrhizal association between fungi and plant roots.! Ectomycorrhizas! Endomycorrhizas 13 14 Root Nodules Mycorrhizas 15 16
Transport Mechanisms in Plants Leaves carry on photosynthesis. Xylem transports water.! Two types of conducting cells. " Tracheids " Vessel Elements! Water flows passively from an area of higher water potential to an area of lower water potential. 17 18 Conducting Cells of Xylem Transport Mechanisms in Plants Phloem transports organic materials.! Conducting cells are sieve-tube members. " Have companion cells to provide proteins. " End walls are sieve plates. # Plasmodesmata extend through sieve plates. 19 20
Plant Transport System Water Transport Water entering roots creates a positive pressure (root pressure). Pushes xylem sap upward. May be responsible for guttation.! Water forced out vein endings along edges of leaves. 21 22 Cohesion-Tension Model Cohesion-tension model of xylem transport suggests a passive xylem transport. Water molecules tend to cling together. Polarity of water allows interaction with molecules of vessel walls. Water column moves passively upward due to transpiration.! Column must be continuous.! Waxy cuticle prevents water loss. 23 Fig. 26.11 24
Opening and Closing of Stomata Each stomata in leaf epidermis is bordered by guard cells. Increased turgor pressure opens stomata.! Active transport of K + into guard cells. 25 26 Role of Phloem Organic Nutrient Transport Girdling of tree (removing strip of bark) below the level of majority of leaves causes bark to swell just above the cut.! Sugar accumulates in the swollen tissue. " Phloem transports sugar Pressure-Flow of Phloem Transport Positive pressure drives sap in sieve tubes. Sucrose is actively transported in sieve tubes, and water flows by osmosis.! Increase in pressure creates flow that moves water and sucrose to a sink. 27 28
Pressure-Flow of Phloem Transport 29 30 31 32
Review Essential Inorganic Nutrients Soil Formation Soil Profiles Soil Erosion Mineral Uptake Transport Mechanisms Water Organic Nutrients 33