mineral nutrition. mineral nutrition - overview some minerals can be used as is: –e.g. some...
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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
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.
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, clayLarge, 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 NNH4
NO3Decomposit
ion
N2
Ammonification Nitrification
Immobilization
Uptake
Leaching
Denitrification
N2 fixation
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
2. Carnivorous plants
• Digest animals & insects – why?
• Motor cells!
• Ex. Venus flytrap, pitcher plant, Darlingtonia
3. Mycorrhizal relationships
• Plants get greater SA for water & phosphorus uptake
• Almost all plant species!
Three levels of transport in plants:
1. Cellular –
2. Short-distance –
3. Long-distance – throughout whole plant (xylem & phloem)
Guard cells
• control stomatal diameter by changing shape.
– Lose water, become flaccid, stomata close
Guard cells
• Opening Mechanism:
– Sunlight, circadian rhythms, & low CO2
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
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
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
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
• Desert plants have adaptations to increase their WUE:
– High-volume water storage (cacti)– Crassulacean Acid Metabolism (CAM) – plants take
in CO2 only at night, so that stomata only have to be open at night.
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