BIOA02 LECTURE 10: Plant Nutrition and Soils

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Published on 4 Feb 2012
School
UTSC
Department
Biological Sciences
Course
BIOA02H3
Professor
BIOA02 Lecture 10: Plant nutrition and soils
January 30, 2012
Nutrients necessary for plant life
-element necessary to life ordered in importance (w/ respect to
molybdenum)
-nutrients needed in large amounts macronutrients
-nutrient needed in small amounts micronutrient
-absence of either types of nutrients prevents the plant from
completing its life cycle
-NPK (nitrogen, phosphorus, potassium) ratio how much of each
macronutrient is in the fertilizer
Nitrogen
-nitrogen needed for basic metabolic pathways
-nitrogen tends to be limit but it is also abundant in the atmosphere
(78%) but only one class can access this nitrogen (bacteria) which
have to fix it and the bacteria make it available secondarily to all living
organism
-young soil tend to have limited nitrogen because bacteria needs to
break down and have the nitrogen to accumulate (needs several
thousand years to be build up)
-young soils need to have accumulation of soil in order for plants and
animals to use it
-nitrogen is used in the building blocks of life: amino acids which are
used to make protein
-nitrogen is also needed in photosynthesis: chlorophyll a and
chlorophyll b, needed for ATP and NADP which have more than one
nitrogen atom, and DNA
-nitrogen cycle:
-bacteria is the key players to make atmosphere nitrogen to
plants and then to animals
-the only way nitrogen becomes bioavailable besides through
bacteria, is through lightning a lot of pressure and heat which
are key components needed to move inert nitrogen gas to
accessible nitrogen
-however the amount is negligible therefore bacteria is
needed
-two ways in which bacteria fix nitrogen:
1) free-living soil bacteria in the soil and have the
metabolic tools and pathways to access atmospheric
nitrogen and fix it to turn it into nitrogen and they use
this nitrogen for themselves and when they die, they
decompose amino acids get broken down into
ammonia and get converted into nitrate and nitrite
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-nitrate is the most bioaccessible to plants nitrogen
type the plants take up by their roots and incorporate
into their molecules
2) symbiotic bactera live on the root of plants and fix
atmospheric nitrogen and make up some of the extra
nitrogen which they don’t need forthemselves directrly
available to the plants
-when plants die, they decompose and soil bacteria
break down the nitrogen of the dead plants
-or animals eat the plants and when the animal die, they
decompose (this completes the cycle)
-or animals urinate and the urea and uric acid contains
nitrogen which enters the soil and through more soil
bacteria it is turned into ammonia and nitrate and the
cycle closes
-if there is an excess of nitrogen in the soils, the nitrogen gets
denitrified and turns into nitrogen gas
-the key steps of the nitrogen cycle is all done by bacteria: fixing
the nitrogen in the atmosphere, decomposing animals and
obtaining nitrogen and detrification of nitrogen
Phosphorus
-needed for growth (i.e. for cell division, root and tissue growth)
-needed for flowers and fruits
-hardest macronutrient to access by plant root because it’s highly
reactive and it precipitates falls out of solution
-any mineral plant wants to access needs to be dissolved in water
therefore phosphorous is mostly biounavailable (there may be a lot of
phosphorus cannot be taken up)
-phosphorus is found in RNA and DNA (phosphate backbone), found in
ATP and NADP
Potassium
-especially important for plants when they produce sugar and starch
-often involved in production of fruit
-key element in controlling opening and closing of stomata so plants
don’t have water shortage
-needed to resist some disease enzyme activated by potassium
key element in photosynthesis
-binds very easily to soil particles more bioavailable compared to
phosphorus
-can educate your eye to detect what kind of shortages plants can
have by looking at the colour of the leaves
Nutrient availability in soils
Nutrient charge
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