Mineral Nutrition PDF

Mineral Nutrition CHAPTER 5 CO2 Minerals H2O O2 Why is plant nutrition so important for us? • OUR CROPS! – Fertilizers – Which are the most common “ingredients” in fertilizers? WHERE DO WE GET THESE FROM? Why is plant nutrition so important for us? • OUR CROPS! – Problems with fertilizers?...

Mineral Nutrition CHAPTER 5 CO2 Minerals H2O O2 Why is plant nutrition so important for us? • OUR CROPS! – Fertilizers – Which are the most common “ingredients” in fertilizers? WHERE DO WE GET THESE FROM? Why is plant nutrition so important for us? • OUR CROPS! – Problems with fertilizers? Figure 32.7A The effect of nitrogen availability on corn growth: corn grown in nitrogen-rich soil (left) and nitrogen-poor soil (right). Classifying mineral nutrients • • • • Amount required or present in plant tissue Metabolic need for the mineral nutrient Biochemical function(s) for the mineral nutrient Mobility within the plant Essentiality of mineral nutrients Essential: Universal for all plants • Absence prevents completion of life cycle • Absence leads to deficiency • Required for some aspect of mineral nutrition Beneficial: Often limited to a few species • Stimulates growth and development • May be required in some species • Examples: Na, Si, Se. Cobalt required for N-fixing species only for development of nodules Mineral macronutrients Mineral micronutrients Biochemical functions of mineral nutrients There are four basic groups: Forms organic components Are assimilated via biochemical reactions Energy storage reactions or maintaining structural integrity - Enzyme cofactors - Regulation of osmotic potentials à Ca2+ secondary messenger-amount determines state of stress Biochemical functions of mineral nutrients Important role in reactions involving electron transfer Some also involved in the formation/regulation of plant growth hormones – Zinc The light reaction of photosynthesis - Copper Techniques used to study plant nutrition Hydroponic and Aeroponic systems for growing plants in nutrient solutions in which composition and pH can be automatically controlled. (A) Hydroponic system: the roots are immersed in the nutrient solution, and air is bubbled through the solution. (B) An alternative hydroponic system, is the nutrient film growth system. The nutrient solution is pumped as a thin film down a shallow trough surrounding the plant roots. The composition and pH of the nutrient solution can be controlled automatically. (C) Aeroponic system: roots are suspended over the nutrient solution, which is whipped into a mist by a motor-driven rotor. Nutrient deficiencies Mineral nutrient deficiencies occur when the concentration of a nutrient decreases below a typical range Deficiencies of specific nutrients lead to specific visual, often characteristic, symptoms reflective of the role of that nutrient in plant metabolism Chlorosis Necrosis Patterns of deficiency • The location where a deficiency reflects the mobility of a nutrient • Nutrients are redistributed in the phloem • Old leaves = mobile • Young = immobile Patterns of deficiency Nutrient deficiency vs sufficiency Importance for our crops: has determined the schedules for fertilization How are mineral nutrients acquired by plants? 1. Uptake through the leaves • Artificial: called foliar application. Used to apply iron, copper and manganese. Diffusion through cuticle & stomata 2. Uptake by the roots (soil composition is very important!) 3. Associations with mycorrhizal fungi/bacteria • Fungi/bacteria help with root absorption How are mineral nutrients acquired by plants? 1. Uptake through the leaves • Artificial: called foliar application. Used to apply iron, copper, manganese, nitrogen. Diffusion through cuticle & stomata 2. Uptake by the roots (soil composition is very important!) 3. Associations with mycorrhizal fungi/bacteria • Fungi/bacteria help with root absorption How are mineral nutrients acquired by plants? 1. Uptake through the leaves • Artificial: called foliar application. Used to apply iron, copper, manganese, nitrogen. Diffusion through cuticle & stomata 2. Uptake by the roots (soil composition is very important!) 3. Associations with mycorrhizal fungi/bacteria • Fungi/bacteria help with root absorption ROOTS Adaptations for water-logged soils Rice is special among crops because it is flood-tolerant. They are LIVING, respiring tissues, and therefore require oxygen. Roots can suffocate. Hollow stems to conduct O2 from surface to roots Will water enter or leave these roots? Roots = 50 M NaCl 20 M NaCl Which will absorb more water? Roots = 200 M NaCl Roots = 20 M NaCl 10 M NaCl 10 M NaCl What affects soil pH? • Chemical composition of soil and bedrock • Cation exchange that roots perform decreases pH of soil • Cellular respiration of soil organisms, including decomposers, decreases pH • Acid precipitation sulfuric and nitric acids in atmosphere fall to ground as acid rain, sleet, snow, fog à decreases pH ** pH affects plant root and soil microbe growth ** Root growth favored @ pH of 5.5 to 6.5 The soil affects nutrient absorption Solubility of certain minerals varies with pH • Acidic conditions à releases potassium, magnesium, calcium, and manganese • The decomposition of organic material lowers pH • Binding cations decreases with increasing soil acidity • Rainfall leaches ions à to form alkaline conditions Plants actively pump solutes into their roots in order to maintain hypertonicity relative to their surroundings (sometimes 100x higher solute concentrations) The soil affects nutrient absorption • Negatively charged soil particles affect the absorption of mineral nutrients • Cation exchange occurs on the surface of the soil particle • Cations (+ charged ions) bind to soil as it is (–) charged If K+ binds to the soil it can displace Ca2+ from the soil particle and make it available for uptake by the root Cation exchange capacity: the capacity for the soil to bind positively charged ions Low High Cation binding capacity Clay is made of layers and layers of thin sheets = LOTS of surface area for cation binding; the problem is that these small particles pack together so tightly, that roots can’t breathe and water can’t percolate. Soil particles have a (-) charge. There is a “pecking” order determining which cations stick to soil best. Small ions (e.g. H+) bind soil the most tightly, and so does aluminum (3+). Roots excrete H+ ions to displace other, probably more useful, ions (“cation exchange”) If soil pH is too acidic, H+ ions will hog the soil particle and all the nutrients will just leach through the soil H H H H H H H Ca2+ H H H H H H H H H H H H H Mg2+ “Liming” the soil involves adding bases (like chalk and limestone) to the soil to bind to the H+ CaCO3 + H2O ↔ Ca2+ + HCO3- + OHH H H H H H H H H H H H2 O H H H H H H H H H H H H H H H H H Ca H H H H H H H H H H H 2+ Root absorbs different mineral ions in different areas • Calcium – Apical region • Iron – Apical region (barley) – Or entire root (corn) • Potassium, nitrate, ammonium, and phosphate – All locations of root surface – In corn and rice, root apex absorbs ammonium faster – In several species, root hairs are the most active phosphate absorbers Why should root tips be the primary site of nutrient uptake? • Tissues with greatest need for nutrients – Cell elongation requires potassium, nitrate, and chlorine to increase osmotic pressure within the wall – Ammonium is a good nitrogen source for cell division in meristem – Apex grows into fresh soil and finds fresh supplies of nutrients • Nutrients are carried via bulk flow with water, and water enters near tips • Maintain concentration gradients for mineral nutrient transport and uptake Root uptake soon depletes nutrients near the roots • Nutrient depletion zone near the plant root – When rate of nutrient uptake exceeds rate of replacement in soil – Root associations with Mycorrhizal fungi help the plant overcome this problem Particularly important for phosphate Assimilation of Inorganic Nutrients CHAPTER 13 Nutrient assimilation • • • • Nitrogen Sulfur Phosphate Cation (Iron) Manipulating mineral transport in plants • Increase plant growth and yield • Increase plant nutritional quality and density • Increase removal of soil contaminants (as in phytoremediation) Ca. 78% of the atmosphere is composed of N2 Why is it so hard to get if it is so abundant? 90% 8 & 2% This could produce better, cheaper and safer fertilizers… but why isn‘t it used? NH3 + H2O Plant residue → (Protein, aa, etc.) NH4+ NH4+ + OH→ Ammonium NO2 Nitrite → NO3Nitrate 1. Nitrogen (N) Soil Nitrogen Cycle N functions: Component of proteins, enzymes, amino acids, nucleic acids, chlorophyll C/N ratio (Carbohydrate: Nitrogen ratio) High C/N ratio → Plants more reproductive Low C/N ratio→ Plants more vegetative Essential for fast growth, green color Deficiency and Toxicity Symptoms Deficiency: Reduced growth, yellowing of old leaves Toxicity (excess): Shoot elongation, dark leaves, succulence Fertilizers Rhizobium (symbiotic) found in legumes Azotobacter (non-symbiotic bacteria) - Most plants prefer 50:50 NH4+ : NO3NH4+ - form of N → lowers soil pH NO3- - form of N → raises soil pH Organic fertilizers (manure, plant residue) – slow acting N can be applied in leaves Unassimilated ammonium or nitrate can be toxic Plants store excess ammonium in the vacuole Nitrate can be translocated without deleterious effects but if we eat it à health issues (Carcinogens, issues with liver, widening of blood vessels) 2. Sulfur (S) Very versatile. Role in structural and regulatory roles Soil Relations - Present in mineral pyrite (FeS2, fool’s gold), sulfides (S-mineral complex), sulfates (involving SO4-2) - Mostly contained in organic matter; acid rain Plant Functions - Component of amino acids (methionine, cysteine) - Constituent of coenzymes and vitamins - Responsible for pungency and flavor (onion, garlic, mustard) - Toxicity: not commonly seen Leaves are more active than roots in sulfur assimilation. Sulfur is needed in photosynthesis & photorespiration, thus it is more useful there 3. Phosphorus (P) as phosphate HPO42Soil Relations - Mineral apatite [Ca5F(PO4)3] - Relatively stable in soil - Has a low mobility Plant Functions - Component of nucleic acid (DNA, RNA), phospholipids, coenzymes, high-energy phosphate bonds (ADP, ATP) - Seeds are high in P Deficiency and Toxicity - P is mobile in plant tissues (Deficiency occurs in older leaves) - Deficiency: dark, purplish color on older leaves - Excess P: causes deficiency symptoms of Zn, Cu, Fe, Mn 4. Cations (iron) Component of cytochromes (needed for photosynthesis) Essential for N fixation (nitrate reductase) and respiration Deficiency: Interveinal chlorosis on new growth; develops when soil pH is high. Fe is immobile Remedy for iron chlorosis: 1) Use iron chelates 2) Lower soil pH Iron is in more useful form (Fe2+) 1-Piggyback Plant, 2- Petunia, 3-Silver Maple, 4-Rose (A-normal, B-Fe-deficient) Energetics of nutrient assimilation • Lots of energy needed to convert stable, low-energy, highly oxidized inorganic compounds into highenergy, highly reduced, organic compounds – Plants may use ¼ of their energy to assimilate N and it accounts for < 2% of their dry weight! – Wheat has already suffered losses in food quality: more CO2, less shoot nitrate assimilation (less photorespiration) Roots and Mutualists (Mycorrhizae) CHAPTER 5,13 How are mineral nutrients acquired by plants? 1. Uptake through the leaves • Artificial: called foliar application. Used to apply iron, copper and manganese. Diffusion through cuticle & stomata 2. Uptake by the roots (soil composition is very important!) 3. Associations with mycorrhizal fungi/bacteria • Fungi/bacteria help with root absorption SOIL DIVERSITY Mycorrhizae Plant supplies carbohydrates Fungi supply nutrients Root hairs & mycorrhizae are critical for maximizing surface area Mycorrhizal associations • Very common! – 90% of land plants (incl. crops) – Majority (ca. 80%) arbuscular • Two main types: arbuscular & ectomycorrhizae • Symbiosis ~ 450 mya, but ecto. is more recent • Fungi: – Basidiomycota+, Ascomycota (ecto) – Glomeromycota (arbuscular) • Very important for crops • Some practices eliminate them: flooding, soil disturbance (plowing), high concentrations of fertilizer, soil fumigation. – Not found in hydroponics Micorrhizal network http://www.bbc.com/earth/story/20141111-plants-havea-hidden-internet http://www.bbc.com/news/science-environment-22462855 DOUGLAS FIR (Pseudotsuga menziesii) Mycorrhizal associations Do not penetrate endodermis Vesicular arbuscular mycorrhizae – Hyphae grow in dense arrangement. Promotes good soil structure. – Enters root (by root hair or through epidermis) à hyphae move through regions between cells à penetrate individual cortex cells – Within cells: oval structures – vesicles – and branched structures – arbuscules (site of nutrient transfer) – P, Cu, & Zn absorption improved – Highly efficient absorption, rapid translocation & transfer of nutrients Figure 32.13A A mycorrhiza on a eucalyptus root. By simple diffusion from the arbuscules to the root cells. Also, nutrients may be released directly into the host cell Mycorrhizal associations Ectotrophic Mycorrhizal fungi – Thick sheath around root – Some mycelium penetrates the cortex cells. If not penetrated à Hartig net – More nutrient absorption – hyphae are finer than root hairs – Fewer plant spp; Pinaceae, Fagaceae, Salicaceae*, Betulaceae, Myrtaceae*. Nutrients move by simple diffusion from the hyphae in the Hartig net to the root cells Bacteria Found in Fabaceae; N2-fixing Rhizobium spp. Kudzu, clovers, soybeans, alfalfa, lupines, peanuts, rooibos, Inga ROOT NODULES: Nitrogen has to be fixed in anaerobic conditions à when associated with plants, nodules are formed Mainly around the elongation zone and root hairs Bacteria within vesicle Figure 32.13C Bacteria within a root nodule cell. Atmosphere Soil bacteria convert N2 gas from the air into forms usable by plants via several processes N2 Soil – Nitrogen fixation—N2 is converted to ammonia – Amonification—conversion of organic matter into ammonium – Nitrification—conversion of ammonium to nitrates, the form most often taken up by plants Amino acids, etc. N2 Nitrogen-fixing bacteria H+ NH3 Ammonifying Organic bacteria material NH4+ NH4+ NO3– (ammonium) Nitrifying (nitrate) bacteria Root Life on Earth depends on N-fixation carried out exclusively by certain N-fixing bacteria that reduce N2 to NH3 through reaction sequence mediated by one enzyme complex: nitrogenase Plants acquire nitrogen mainly as nitrate (NO3-), which is produced in the soil by nitrifying bacteria that oxidize ammonium (NH4+) to NO3- Beneficial services: Iron and other nutrient uptake, controls harmful soil organisms PARCIAL 1 • • • • • Anatomía: Cap. 1 Pared celular: Cap. 14 Movimiento del agua: Cap. 3 Relaciones hídricas: Cap. 4 Nutrición: Cap. 5, 13