Transcript Document

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,
Large,
spaces
for water
& air
silt,
clay
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
N2
N2 fixation
Denitrification
Uptake
NO3
Organic N
NH4
Leaching
Nitrogen Fixation
•
conversion of N2 in air to NH3 by
microbes
But N is also lost….
• Leaching –
• Denitrification – conversion of NO3- back to
N2
All steps within the soil are mediated by bacteria!!!!
Fig 37.9
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
http://www.nofc.forestry.ca/publications/leaflets/mistletoe_e.html
http://cals.arizona.edu/pubs/diseases/az1309/
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 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
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 CO2 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