Lecture 27 - Plant Nutrition (part 2) Flashcards
Sugars travel from…
source to sinks
Bulk flow within xylem is…
unidirectional -> Roots to shoots
Translocation
is the transport of photosynthates
- is carried out by the phloem in the opposite direction -> shoots downward to stems and roots
Phloem sap
is the aqueous solution that flows through the phloem cells (sieve tubes)
What does phloem sap contain?
- Contains mostly dissolved sugars (sucrose in most species)
* Can also contain amino acids, hormones, and minerals
Phloem sap moves from…
sources to sinks
Sinks
net consumers of sugars or will store sugar deposits
- roots, buds, stems, fruits, growing leaves and tissues
Sources
plant organ that is a net producer of sugar
- mature leaves
Storage organs can be both…
sources and sinks depending on the season
Storage organs in the Summer:
sugar stockpiling in the storage bulbs/tubers (sink)
Storage organs in the Spring:
supplies sugar for initial growth (source)
Sinks receive sugars from their nearest source…
upper leaves export to buds, lower leaves export to roots
Sugars must be “loaded” into sieve-tube elements before being _________
exported to sinks
Sugars must be “loaded” which can be done by what?
- Can be done symplastically through plasmodesmata from mesophyll cells to sieve-tube elements
- Other species can load sugar both symplastically and apoplastically
- Requires active transport via proton pumping and H+/sucrose cotransporters
Sugars are “unloaded” at sinks via _________
facilitated diffusion
Concentration of free sugar in the sink is always _____ than the sieve-tube elements
lower
Bulk flow of phloem sap is via…
+ pressure (pressure flow)
Sugars are loaded into phloem sap by _______, which ______ the water potential of the phloem sap in that region.
This causes water to move into the _______ from nearby cells or surrounding xylem tissue
source cells
lowers
phloem sap
The increase in water pressure forces phloem sap to…
move through the sieve tubes
At sink cells, phloem is unloaded…
INCREASING water potential & causes water to LEAVE the phloem sap and ENTER nearby cells and xylem
Xylem then recycles water from…
sink to source
Sometimes a plant can have too many…
sinks
• Can abort buds, fruits, and seeds through selfthinning
• We use this concept to make larger apples to sell in markets
Plants acquire nutrients from the…
soil
Plants absorb nearly all of their water and minerals from what?
top layers of soil
What does top layers of soil contain?
a slew of microorganisms that can associate with plants
Soil texture is dependent on particle size as a result of…
rock weathering
Coarse sand:
0.02-2mm in diameter
Silt:
0.002-0.019mm
Clay particles:
<0.002mm
Soil composition forms layers called
horizons
Topsoils
Horizon A, consists of humus (organic matter) and soil particles
Plants get their nutrients from what?
the soil solution (between the particles)
Sandy soils are not good at _________, but have ________
water retention
good oxygen exchange
Clayey soils retain too much ______, lack _______
water
oxygen
Loams
are the most fertile topsoil, consisting of pores of 50% water, 50% air
Topsoil is composed of both:
- Inorganic compounds
* Organic compounds
Inorganic compounds
- Soil particles are generally negatively charged -> bind with positive cations K+, Mg2+, Ca2+
- Don’t bind with nitrates, phosphates, sulphates (anions) -> but plants need these!
Organic compounds
Mostly humus, organic material composed by decaying leaves, feces, dead organisms, bacteria, and fungi
What does organic compounds prevent?
Prevents clay particles from sticking together
- so retains water but allows for some drainage
Plants do not obtain ______ directly from the soil
nutrients
Nutrients are dissolved into the soil solution via…
cation exchange
Cation exchange
- Cations are displaced from soil particles by other cations (H+)
- Dependent on pH and adhesion sites
- More clay and organic material in the soil, more cation exchange
Humans can dramatically change the…
soil quality
We know that fertilisation increases…
nutrient levels in the soil
Increases in nutrient levels in the soil helps overcome…
decrease plant yields over successive years of farming by providing N, P, K
Resulted in civilisation –>
we can now sit and wait for our food rather than gather surrounding resources
Increase nutrient levels in the soil also result in…
soil mismanagement and nutrient overloading of ecosystems
Describe soil mismanagement and nutrient overloading of ecosystems…
- Removal of native plant species with deep roots can erode away the topsoil, leaving behind soil of poor nutrient quality
- Lake Winnipeg nutrient enrichment leads to massive algal blooms and toxic aquatic conditions
Where can water be very limiting in?
arid regions or areas with longer days (equatorial)
Irrigation allows for water to be…
diverted to the soils
Water has lots of dissolved nutrients, so can increase…
soil nutrient levels to a point
Too much irrigation can leave behind…
salts due to evaporation, which can decrease the plant’s ability to absorb water
Soil pH can affect the plant’s ability for…
cation exchange
Most plants prefer…
slightly acidic soil
pH 8 ->
plants absorb calcium, but not iron
pH 5 or lower ->
toxic minerals such as aluminum become more soluble and are absorbed by the roots
Water and wind erosion can remove…
layers of topsoil
• Removal of native grass species no longer anchor the soil
Wind & wind erosion can counteract that with…
wind breaks, terrace hillside crops, contour patterns of crop cultivation
Phytoremediation
is a non-destructive biotechnology that uses the special ability of some plant species to remove contaminants/pollution from soil
Dr. Renault and Dr. Markham have studied the effect of using…
dogwoods and cattail species to revegetate gold mine tailing sites and areas of high salinity and toxic substances
Plants need…
essential elements to grow
Essential elements
are needed to complete a plant’s life cycle and reproduce
Macronutrients
9 essential elements needed in relative larger amounts
• C, O, H, N, P, S, K, Ca, Mg
Micronutrients
need only in minute quantities
• Cl, Fe, Mn, B, Zn, Cu, Ni, Mb (and sometimes Na)
Plants lacking enough essential elements show signs of what?
nutrient deficiency
What does nutrient deficiency affect?
Affect the plant’s function, development, and life cycle
Chlorosis
Mg deficiency, causes chlorophyll to break down and turn leaves yellow (though it could also be caused by iron deficiency since Fe is used as a cofactor in chlorophyll synthesis)
If nutrients move freely, symptoms of nutrient deficiency appear in the…
older tissues/organs first
Mg is a mobile element ->
gets shunted to younger leaves if not enough is obtained
Immobile elements shortages show up in the…
younger tissues
• Ie. Iron is immobile and causes young leaves to turn yellow
Plants nutrition depends on what?
interactions
Plants can enhance nutrient acquisition through what?
associations and interactions with bacteria and fungi
Rhizobacteria
- Live associated with plant roots or in the rhizosphere (soil surrounding plant roots)
- Depend on the nutrients secreted from plant roots
- Provide a variety of benefits
- Can be free-living in the rhizosphere or endophytic in plant roots, producing nodule
What are the variety of benefits that Rhizobacteria provides?
- antibiotics to prevent root disease
- absorb toxic materials so plants do not absorb them
- Nitrogen fixation
Nitrogen fixation
converting atmosphere N2 gas to ammonium/nitrate (NH3)
All nitrogen-fixing organisms are what?
bacteria
If nitrogen fixation is associated with plants…
form nodules on the roots (Rhizobium spp., in soybean, other legumes)
What is nitrogen fixation driven by?
the enzyme nitrogenase
nitrogenase
energy intensive which is why N-fixing bacteria need plant associations
Ammonification
organic nitrogen (from decaying matter) is converted to NH3 or NH4+
Nitrifying
Oxidises ammonium to nitrite and nitrite to nitrate
Denitrifying
Nitrates are reduced back to nitrogen gas
Farmers can utilise plants that associate with N-fixing bacteria in their crop rotations to help what?
to help return nitrogen back into the soil for the next year’s crops
Plants can also associate with…
mycorrhizal fungi -> evolutionary adaptation to moving onto land
Ectomycorrhizal fungi
- Form a dense sheath of mycelia around the plant roots, roots do not form root hairs
- Hyphae can also grow into the root cortex and inhabit the apoplast
- 10% of plant species associate with this kind of mycorrhizal fungi (pine, oak, birch, eucalyptus)
Arbuscular mycorrhizal fungi
- Also called ENDOmycorrhizal fungi
* EMBEDDED within the plant root, forming arbuscules
Crop yields can often depend on what?
the association with mycorrhizae
Planting seeds from one area to another can result in…
plants of poor health since they lack their natural mycorrhizal associations
Plants can acquire nutrients from animals…
- Dead salmon decompose, releasing nitrogen into terrestrial ecosystems surrounding streams
- Carnivorous plants
Carnivorous plants
Photosynthesise but acquire nutrients (microelements and nitrogen) from digesting insects and small animals
Plants can acquire nutrients from other plants…
- Epiphytes
* Parasitic plants
Plants can acquire nutrients from what?
animals & other plants
Epiphytes
- Plant grows on another plant
* They produce their own food and acquire their own nutrients (do not tap into the plant it is living on)
Parasitic plants
- Absorb water, nutrients, and sometimes photosynthates from the host plant
- Roots function as haustoria
Carnivorous plants examples
Sundews, butterworts, Venus fly traps
Epiphytes examples
- Staghorn ferns
- Air plants
- Orchids
- Bromeliads
Parasitic plants examples
- Ex. Dwarf mistletoe only steals water and minerals
* Ex. Monotropa uniflora absorbs nutrients from the mycorrhizae associated with other plants
