Plant nutrition Flashcards
What is plant nutrition?
The study of the chemical elements necessary for plant growth & the adaptations for obtaining these elements
80-90% of a plant’s fresh mass is what?
Water
4% of a plant’s dry mass is what?
What is the other 96%?
Inorganic substances from soil
From CO2 assimilated during photosynthesis
What are essential elements?
Required for plants to survive (complete its life cycle) & reproduce
What % do micronutrients make up in some species?
0.02% of dry weight
What are most fertilisers?
NPK
= major macronutrients essential for healthy plant growth
Give examples of macronutrients
Carbon Oxygen Hydrogen Nitrogen Potassium Calcium Magnesium Phosphorous Sulfar
Give an example of a micronutrient and what it’s used for
Manganese
- crucial for amino acid formation & photosynthesis
Which is the most abundant macronutrient that isn’t C, H or O2?
Nitrogen
What is N a component of?
Amino acids Nucleic acids Cofactors Hormones Alkaloids Chlorophyll
What is hydroponic culture used for?
Determining which chemical elements are essential
What do symptoms of mineral deficiency depend on?
Nutrient’s function & mobility within the plant
What does deficiency of a mobile nutrient affect?
Give an example
Older organs
Magnesium
What does deficiency of an immobile nutrient affect?
Give an example
Younger organs
Iron
Why are older organs affected more in mobile nutrient deficiency?
Mobile nutrients can be transported to actively growing young tissues from older tissues
- so older organs display the deficiency
What are the most common deficiencies?
N
P
K
What is a key factor that affect nutrient availability?
pH
In which pH are there:
> major nutrient deficiencies?
> trace element deficiencies?
> Acidic
> Alkaline
How do some species survive in acidic & alkaline soils?
> ability to interact w/ other orgs in soil
> can change chemistry of soil around them to facilitate getting hold of macronutrients
Define chlorosis
Yellowing due to loss of chlorophyll
Define necrosis
Death of plant tissue
What are the symptoms of N deficiency?
> little growth
> yellowing of mature lower leaves
What type of nutrient is N?
Mobile macronutrient
What are the 2 forms N is acquired in?
> nitrate - favoured as benign & chemically unreactive
> ammonia - toxic as breaks down e- transport
Soil is stratified into layers called…?
Soil horizons
Which horizon plants obtain most of their water & minerals from?
A horizon
- topsoil
What does topsoil consist of?
> mineral particles
living orgs
humus (decaying organic material)
What are the basic physical properties of soil?
Texture
Composition (organic & inorganic)
What is the B horizon made up of?
Less organic material than A
Less weathered than A
What is the C horizon made of?
Partially broken down rock
Why can clay particles hold onto water?
They’re -vely charged
How is soil formed?
By gradual disintegration of rocks
+ decaying organic matter integrates into soil aggregates
What are cations?
Give examples.
What do they do to soil particles & why?
+ve charged ions
K+, Ca2+,Mg2+
Adhere to them
Particles are -vely charged
What happens in cation exchange?
Cations are displaced from soil particles by H+ ions produced directly or indirectly by plant roots
- -> displace cations enter soil solution
- -> can be taken up by plant roots
How can H+ ions be released indirectly by plant roots?
CO2 from respiration released from plant roots
- -> produces carbonic acid
- -> releases H+ ions
How can plant nutrition sometimes depend on mutualistic relationships w/ soil microbes?
> secretions from roots support microbes in nearby enviro
> microbes in rhizosphere help plant obtain nutrients
What are endophytic bacteria?
Those that live between cells in plant roots
What is the rhizosphere?
Layer of soil surrounding the growing root that is affected by the root
- no sharp boundary
What is rhizodeposition?
The secretion of organic compounds e.g. sugars, amino acids & organic acids by plant roots into the rhizosphere
What do rhizodeposits consist of?
> sloughed off cells (by friction w/ soil)
> organic matter exuded (from living cells)
Why is rhizodeposition of ecological importance?
> loss of C for the plant
input from organic C pool of the soil
field the soil microbiota
What are rhizobacteria?
Bacteria that live in the rhizosphere
What are the roles of rhizobacteria?
> produce hormone-like substances = stimulate plant growth
produce antibiotics = protect roots from disease
absorb toxic metals/ make nutrients more available to roots
What are the roles of soil bacteria in plant N nutrition?
N-fixing bacteria e.g. Rhizobia
(N gas –> ammonia)
Ammonifying bacteria
(humus –> ammonia)
Nitrifying bacteria
(ammonium –> nitrate)
Denitrifying bacteria
(nitrate –> N gas)
Why isn’t N directly available to plants?
Requires breaking of v stable covalent triple bond
plants can’t do
What are mycorrhizae?
Mutualistic associations of fungi & roots
- increase absorption capacity of plant
- fungi gain carbohydrates
What are the 2 types of mycorrhizae?
Ectomycorrhizae
- grows on surface of roots & between cells
Endomycorrhizae
(arbuscular mycorrhizae)
- gets into cytoplasm of cell
What are the nutritional adaptations using other orgs in a non-mutualistic way?
Epiphytes
Parasitic plants
Carnivorous plants
What are epiphytes?
Plants that grow on surface of plants and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it.
What are the different examples of types of parasitic plants?
Mistletoe = photosynthetic
Dodder = non photosynthetic
Indian pipe = non photosynthetic parasite of mycorrhizae
Describe carnivorous plants
> Photosynthetic
Obtain N by killing & digesting insects
Adaptation to low nutrient enviro e.g. bogs
Traps = modified leaves
What are the 2 types of traps & give examples
Active
e.g. Venus fly trap
Passive
e.g. Pitcher plants
What are the costs of botanical carnivory?
> underdeveloped root system
traps not v good at photosynthesis
= trade-off between light capture & prey capture
