Mineral NutritionHORT 301 – Plant Physiology

October 5, 2007Taiz and Zeiger, Chapter 5, Web Topics 5.1 and 5.2

paul.m.hasegawa.1@purdue.edu

Nitrogen in plants

courtesy of Burkhard Schulz

Mineral nutrition – acquisition and utilization by plants of naturally occurring essential mineral elements

Plant nutrient status – based on symptoms (growth, pigmentation, senescence, etc.), and soil and tissue analyses

Mineral nutrient acquisition from the soil – chemical forms and availability of mineral nutrients in the soil solution

Mineral nutrient absorption by roots – uptake from the soil

Mycorrhizal fungi and mineral nutrient absorption by plants – symbiosis that facilitates absorption

Mineral nutrition – acquisition and use of essential mineral nutrients by plants

Naturally occurring minerals (elemental, or simplest chemical or molecular form) that are in soils

Plants access mineral nutrients typically by root absorption from the soil solution

Mineral nutrients are products of recycling of organic matter and soil weathering

Mineral nutrients often limit plant growth, agricultural practice is to optimize the nutrient status of a plant by soil amendment

Essential elements – mineral nutrients that are required by plants for metabolic function, and growth and development

These nutrients together with CO2 and H2O, and sunlight (light energy) allow plants to synthesize all other necessary molecules

An essential mineral nutrient is:

1. a required component of structure (silicon in the cell wall) or plant metabolism

2. necessary for plant growth, development or reproduction

Hydroponics (liquid solution culture) - facilitated determination of essential mineral nutrients

Some micronutrients are required in low amounts, essentiality was difficult to establish using soil

Solution culture requires a synthetic “medium” containing essential nutrients, e.g.Hoagland’s solution

5.1 Various types of solution culture systems (Part 1)

Essential elements are categorized as macronutrients or micronutrients based on relative concentration in plant tissue (dry weight)

Macronutrient – up to 1.5%, 15,000 ppm in dry matter

Micronutrient - 100 ppm (dry matter) or less

Classification of essential mineral nutrients by function

Group 1 (N and S) – components of organic molecules

Group 2 (P, Si, B) – energy storage or cellular structure

Group 3 (K, Ca, Mg, Cl, Mn, Na) – present as ions in cells, enzyme co-factors, osmotic adjustment, signaling

Group 4 (Fe, Zn, Cu, Ni, Mo) – metals involved in redox reactions (electron transfer),

Nutrient deficiency symptoms – soils (generally) have a limited mineral nutrient load capacity

Plant nutrient deficiency symptoms may be used to determine when and what type of soil nutrient amendment (fertilization) is necessary

Symptoms are complex, occurring from deficiency of different individual nutrients and further complicated by stresses, see Web Topic 5.1 for an in-depth treatise of plant nutrient deficiency symptoms

Nutrient Deficiency Symptoms

Nutrient deficiency symptoms – soils (generally) have a limited mineral nutrient load capacity

Plant nutrient deficiency symptoms may be used to determine when and what type of soil nutrient amendment (fertilization) is necessary

Symptoms are complex, occurring from deficiency of different individual nutrients and further complicated by stresses, see Web Topic 5.1 for an in-depth treatise of plant nutrient deficiency symptoms

Plant tissue analysis – a precise method to assesses nutrient status of tissues, used to optimize fertilizer application (crop production + reduced pollution)

Mineral NutritionHORT 301 – Plant Physiology

October 5, 2007Taiz and Zeiger, Chapter 5, Web Topics 5.1 and 5.2

paul.m.hasegawa.1@purdue.edu

Nitrogen in plants

courtesy of Burkhard Schulz

Mineral nutrition – acquisition and utilization by plants of naturally occurring essential mineral elements

Plant nutrient status – based on symptoms (growth, pigmentation, senescence, etc.), and soil and tissue analyses

Mineral nutrient acquisition from the soil – chemical forms and availability of mineral nutrients in the soil solution

Mineral nutrient absorption by roots – uptake from the soil

Mycorrhizal fungi and mineral nutrient absorption by plants – symbiosis that facilitates absorption

Tissue mineral nutrient content zones for plant growth:

Critical concentration - minimum tissue nutrient content for maximum growth or yield

Toxic concentration zone – content at which yield declines because the nutrient is in excess

Adequate zone - determination of adequate zones minimizes fertilization inputs

5.3 Relationship between yield and the nutrient content of the plant tissue

Mobile nutrients (N, K, Mg, P, Cl, Na, Zn and Mo) - symptoms are evident first in older leaves

Immobile nutrients (Ca, S, Fe, B and Cu) - symptoms develop first in the younger leaves

Nutrient Deficiency Symptoms

Mineral nutrient acquisition from the soil - plants access virtually all mineral nutrients from the soil solution

Mineral nutrients – derived from inorganic as well as organic components of the soil rhizosphere

Organic decomposition (microbes) “releases” mineral nutrients to the soil solution (mineralization)

Mineral nutrient forms

Macronutrients

Micronutrients

Soil particles – both inorganic (gravel (>2 mm) to clay (< 2 µm)) and organic soil particles have a negative charge

Cation exchange capacity (CEC) - negatively charged soil particles form electrostatic interactions with cationic mineral nutrients (positively charged ions)

CEC facilitates availability of cations (positively charged elements or molecules) for absorption by plant roots

5.5 The principle of cation exchange on the surface of a soil particle

Negatively charged ions (anions), e.g., NO3-, H2PO4

-, Cl- - remain in the soil solution between particle spaces, adhesion of water

Limited anion exchange capacity of soils - anions form bridges with multivalent cations like Fe2+or Al3+ and H2PO2

-

OR, anions are present in relatively insoluble compounds e.g., SO42-

in gypsum (CaSO4), which are gradually released

Anions are repelled by surface particle charge and tend to be leached through the soil to the ground water

pH and mineralization – affect mineral nutrient availability in soil solution, pH 5.5 to 6.5 is optimal

Decomposition of organic material lowers the pH

Soil amendments alter pH - lime (CaO, CaCO3, Ca(OH)2, attract protons) increases pH (alkaline)Sulfur reduces pH (mineralization results in release of sulfate and hydrogen ions) of the soil solution

5.4 Influence of soil pH on the availability of nutrient elements in organic soils

Shaded area is the relative nutrient availability to plants

Nutrients move in the soil solution to the root surface by pressure-driven bulk flow and diffusion, directly linked to water flow

Root structure and mineral nutrient absorption – roots acquire water and mineral nutrients

As with water, root surface area and absorption is enhanced substantially by production of secondary roots and root hairs

5.7 Taproot system of two adequately watered dicots: sugar beet (A), alfalfa (B)

Roots seek water and nutrients, e.g. water - hydrotropism

5.6 Fibrous root systems of wheat (a monocot)

Effect of Localized Supply of PO4,2-

, NO3- , NH4

+ , and K+ on

Root Growth in Barley

Part of the root system receiving the complete nutrient solution

Part of the root system receiving the nutrient solution deficient in specified nutrient

+-

Drew (1975) New Phytol. 75 : 461-478

Main regions of a primary root are the meristematic zone, elongation and maturation zones

Meristematic – root cap protects the root, gravitropic (gravity response), perhaps other tropic/trophic responses, quiescent zone of meristem initials and cell division for proliferation of cell types

Elongation zone (0.7 to 1.5 mm from apex) – reduced cell division, rapid cellular elongation and development of cell types, including endodermis with Casparian strip, xylem and phloem

Maturation zone – root hair zone that increases the surface area for absorption of water and mineral nutrients

Foliar application facilitates more rapid uptake of mobile elements

Mycorrhizal fungi facilitate water and mineral nutrient uptake into roots – extend the root absorption surface area

Mycorrhiza fungi – symbiotic (sugar for mineral nutrients) association between a fungus and plant roots, 83% of dicot species, 79% of monocots and all gymnosperms

Ectomorphic mycorrhizal fungi – hyphae extend into the cortex (apoplast) of plants and into the soil, up to 100% increase in surface area for nutrient absorption, reduces the nutrient depletion zone at the root surface

5.10 Root infected with ectotrophic mycorrhizal fungi

Vesicular arbuscular mycorrhizal fungi – hyphae are less dense and penetrate into cortical cells where they branch (arbuscule) and transfer nutrients to the plant root, hypae extend from the root facilitating nutrient acquisition beyond the root surface

5.11 Association of vesicular–arbuscular mycorrhizal fungi with a section of a plant root

It is not known precisely how nutrients move from the hyphae to the plant cells, i.e. diffusion or release at hyphal death