Mineral Nutrition

Mineral Nutrition - Overview Some minerals can be used as is: –e.g. Some minerals have to be incorporated into other compounds to be useful: –e.g. Some minerals compounds have to be altered to be useful:

Chemical composition of plants 80–85 % of an herbaceous plant is water. Water is a nutrient since it supplies most of the hydrogen and some oxygen incorporated into organic compounds by photosynthesis. Water also is involved in cell elongation and turgor pressure regulation

Chemical composition of plants: dry weight 95% “organic” – 5% inorganic minerals

Fig 37.2

Essential Nutrients = 2 types: macronutrients & micronutrients

Macronutrients = CHOPKNS CaMg

Micronutrients = elements required by plants in relatively small amounts (<0.1% dry mass). Major functions: –Optimal concentrations highly species specific FeBCl MoCuMnNi Zn

Mineral Deficiency Not common in natural populations. Why? Common in crops & ornamentals. Why? Deficiencies of N, P, and K are the most common. Shortages of micronutrients are less common and often soil type specific. Overdoses of some micronutrients can be toxic.

Fig 37.4

Soils What do soils give to plants??

Soil properties influence mineral nutrition 1.Chemistry – determines which minerals are present and available, thus affecting plant community composition 2.Physical nature – 3.Soil organisms – Nitrogen! The only mineral that the plant can ONLY get from reactions mediated by soil organisms.

Soil texture & composition Soil created by weathering of solid rock by: Topsoil: mix of weathered rock particles & humus (decayed organic matter) Texture: sand, silt, clay Large, spaces for water & air Small, more SA for retaining water & minerals

More about topsoil….. Bacteria, fungi, insects, protists, nematodes, & Earthworms! Humus: Bacterial metabolism recycles nutrients

Availability of soil nutrients Cations in soil water adhere to clay particles (negatively charged surface) Humus – negatively charged & holds water & nutrients. Thus very important in the soil!!!!!

Soil conservation Natural systems: decay recycles nutrients Fertilizers: N:P:K –Synthetic: plant-available, inorganic ions. Faster acting. Problem: –Organic: slow release by cation exchange, holds water, thus less leaching

Why nitrogen? Air is 80% Nitrogen, but….. Macronutrient that is most often limiting. Why? What’s it used for?

The Nitrogen Cycle Organic N NH 4 NO 3 Decomposition N2N2 Ammonification Nitrification Immobilization Uptake Leaching Denitrification N 2 fixation

Nitrogen Fixation conversion of N 2 in air to NH 3 by microbes

But N is also lost…. Leaching – Denitrification – conversion of NO 3 - back to N 2

Fig 37.9 All steps within the soil are mediated by bacteria!!!!

Nitrogen Fixation is catalyzed by the enzyme nitrogenase. Requires energy (ATP) 3 ways: 1.Lightening – 2.Non-symbiotic – 3.Symbiotic

Symbiotic Nitrogen Fixation Legumes: peas, beans, alfalfa Plant – gets ample inorganic N source Bacteria – gets ample carbon source

Fixation in Nonlegumes Here in the NW: alder Azolla (a fern) contains a symbiotic N fixing cyanobacteria useful in rice paddies. Plants with symbiotic N fixers tend to be first colonizers. Why?

Nutritional Adaptations of Plants 1.Parasitic Plants 2.Carnivorous plants 3.Mycorrhizal relationships

1. Parasitic plants. Ex. Mistletoes on Doug Fir & Ponderosa pine Ex. Indian pipe – parasite on trees via mycorrhizae

Fig 37.15

2. Carnivorous plants Digest animals & insects – why? Motor cells! Ex. Venus flytrap, pitcher plant, Darlingtonia

37.16

3. Mycorrhizal relationships Plants get greater SA for water & phosphorus uptake Almost all plant species!

Fig 37.12

Three levels of transport in plants: 1.Cellular – 2.Short-distance – 3.Long-distance – throughout whole plant (xylem & phloem)

Transport at the Cellular Level Diffusion = ? Osmosis – (i.e. water always acts to dilute)

Examples of Short Distance Transport Absorption of water & minerals by roots

Guard cells control stomatal diameter by changing shape. –Lose water, become flaccid, stomata close

Guard cells Opening Mechanism: –Sunlight, circadian rhythms, & low CO 2 concentration in leaf air spaces stimulate the proton pumps & thus stomatal opening

Guard cells Closing mechanism: –Stomatal closure during the day stimulated by water stress – not enough water to keep GCs turgid

Fig 36.15

Motor Cells Motor cells are the “joints” where this flexing occurs. Accumulate or expel potassium to adjust their water levels & thus turgidity. Oxalis – leaves fold in sunlight to minimize transpiration; open in shade Transpiration = loss of water vapor from the stomata

Absorption of water & minerals by roots Soil solution moves freely through epidermal cells & cortex Endodermis – selective barrier to soil solution between cortex & stele. Sealed together by the waxy Casparian strip – Once through the endodermis, soil solution freely enters the xylem

Fig 36.9

Mechanisms of Long Distance Transport Xylem: Phloem: Pushing pressure of water at one end of the sieve tube forces sap to the other end of the tube (= bulk flow).

Transport of xylem sap Pushed by root pressure –Stele has high concentration of minerals. Water flows in, creating pushing pressure

Pulling xylem sap Transpiration – cohesion – tension mechanism Transpirational pull:

Ascent of xylem sap against gravity Aided by: –Adhesion of water to hydrophyllic cell walls of the xylem, –Diameters of tracheids & vessel elements are small, so lots of surface area for adhesion

Control of Transpiration Guard cells! – balance two contrasting needs of the plant:

Desert plants have adaptations to increase their WUE: –High-volume water storage (cacti) –Crassulacean Acid Metabolism (CAM) – plants take in CO 2 only at night, so that stomata only have to be open at night.

Wilting

Translocation of Phloem Sap Sieve tubes carry sap from sugar source (e.g. leaves) to sugar sink (e.g. growing roots, shoot tips, stems, flowers, fruits) Thus not unidirectional –e.g. tubers can be source in spring and sink in fall

Mechanism of phloem translocation Pressure-flow hypothesis: –Thus water flows into sieve tubes, creating hydrostatic pressure (pushing pressure: positive). –Less pressure at sink end, where sugar is leaving sieve tube for consumption –Thus movement from source to sink

Fig 36.18