plant mineral nutrition 3

the form of nitrogen affects the

cation-anion balance

how does nitrate (an anion NO3-) affect cation anion balance

increased levels of nitrate stimulate OM anion synthesis and cation accumulation; the medium becomes alkaline

nitrate-fed plants contain

high levels of cations and organic anions

how does ammonium affect cation-anion balance

ammonium-fed plants contain lower concentrations of cations

which molecule would move into the plant first

potassium due to size

with ammonium, absorbed anions are

presented in higher concentrations like SO₄^2-

with ammonium , the soil becomes more

alkaline

the rate at which an ion is absorbed is dependent on its

concentration in the nutrient medium

growing roots vary both

anatomically and physiologically along their longitudinal axis

the rate of ion uptake are different at

different zones along the root

there is a tendency for the rate of ion uptake per unit root length to decline

as the distance from the apex increases

as pH decreases, in the absence of Ca2+, the net uptake of

K+ declines and below a pH of 4 there is net loss of K+ from roots

in a pH range of 7-4, there is competition between

H+ and K+ for binding sites at the plasma membrane

cation uptake is generally

decreased at a lower pH

anion uptake is either

not affected or slightly stimulated at a lower pH

the effect of pH on nitrogen uptake is dependent on

whether the N is supplied as NH⁴⁺ or NO^-₃

lowering the pH from 7 to 4 decreases the uptake of

the cation NH₄⁺ but increases the uptake of anion NO^-₃

ammonium has an inhibitory effect on the uptake of

metal cations such as K+, Mg2+, Ca2+

absorption of cations is a non-specific process depending mainly on

the concentration of the cation species in the nutrient medium and the membrane permeability

nonspecific competition between the cation species for the

negative charges of the cell can occur

the total sum of cations in a plant or plant tissue changes very

little despite variations in the levels of the individual cations in the nutrient mediums

increasing the supply of one cation species will result in

lowering of the concentration of another cation species

cation species taken up the fastest will neutralize the anion equivalents first thus

reducing the electrostatic attraction for the other cation species

uptake rate is dependent on the particular

cation concentration and the uptake mechanism

potassium is taken up

rapidly and competes strongly in cation uptake

when NO^-₃ uptake is depressed, the uptake of

Cl, SO and H2PO4 is stimulated

the most common anion antagonism is between NO3 and

CL - high supplies of one in the nutrient medium lowers the uptake of the other

stimulation of cation uptake by anions and vice versa may occur and is mainly a

reaction of the necessity of maintaining a charge balance within the cells

the stimulation of K uptake by Ca2 increases with

decreasing pH indicating that Ca counteracts the negative effect of H concentration on K uptake

the effect of calcium on the flux on ions through

metabolism is related to its role in maintaining membrane stability and integrity

what ions are taken up rapidly

NO3, NH4, K, Cl

ions taken up slow

Ca, and SO₄²

differences in uptake rates mean plants remove cations and anions in

unequal amounts from the nutrient medium

these cation-anion uptake imbalances are compensated in the plant by the

accumulation or degredation of organic acid anions and malate in particular

the first plant parts to develop after germination are the

roots

in seedlings the supply of carbs and amino acids is provided by

storage compounds present in the seeds

with development of leaves stems and roots the source of organic material shifts from

the seeds to the leaves

vegetative growth is followed by

reproductive growth which begins with flower initiation, pollination, maturation

as growth progresses photosynthesis are more directed away from

younger meristematic tissues and more towards storage tissues

biological yield

total production of plant material by a crop

economic or commercial yield

takes into account plant organs for which crops are harvested like watermelons

meristematic tissues have a very active protein metabolism and photosynthates transported to these sites are

mainly used to synthesize nucleic acids and proteins

a high growth rate occurs only when

adequate N is available

during the vegetative stage the N nutrition of the plant controls

the plant growth rate

the level on N nutrition needed for optimum vegetative growth must be balances by the

presence of other plant nutrients in adequate amounts

the synthesis of organic N compounds is dependent on

number of ions present, Mg for chlorophyll formation, phosphate for nucleic acids

magnesium is in the

middle of chlorophyll molecule

the mineral nutrient requirement during vegetative growth is determined by

the race of CO2 assimilation

limiting factors include

water, light, temp, nutreints, law of diminishing yield increment

what limiting factors can we not control

light and temp. can control water

water stress limits

cell elongation and division

CO2 assimilation and respiration rates increase with

temperature

law of diminishing yield increment was developed by who

mitscherlich

law of diminishing yield increment states that

when supply of one mineral is increased, other nutrients of the plant become the limiting factor

when there is an abundant supply of nutrients, a point of

inversion is obtained

the inversion point exists for other nutrients and is caused by

toxicity of a nutrient, the induced deficiency of another nutrient

yield response resulting from an increase in one nutrient depends on the

intensity of other nutrients

for the lowest K level the curve indicates

a yield depression at high N levels

mineralization is the process by which

organic matter, organic fertilizers, and some slow release fertilizers are broken down by soil microbes to provide ammonium and nitrate forms of N

aminization and ammonification are process in which proteins, amines, and amino acids are

converted to ammonium which is then absorbed by the plant or transformed to nitrate

nitrification

ammonium nitrogen transformation to nitrate nitrogen

NH₄+ + o2

Nitrosomonas > warm temp

NO₂^- + 2H+

Nitrobacter

nitrification happens in

warm temps, adequate soil moisture and oxygen

during nitrification,

hydrogen ions are produced which reduces soil pH

what factors limit nitrification

below freezing, above 105 F, poorly aerated soil, dry soil, low pH

ammonium nitrogen can be

toxic to plants grown under cool, low light conditions

nitrate nitrogen is very

soluble in water and may leach if not taken up rapidly

drawbacks of nitrification

acidification in soil, N loss in the form of N₂O, resulting nitrate is mobile and may leach into ground water

denitrification

under anaerobic conditions, conversion of nitrate N to gaseous N which may escape into the atmosphere

denitrification happens in

low soil O2 levels, high soil moisture, high pH, compact waterlogged soils

volatilization

conversion of ammonium N to ammonia gas NH₃^- which escapes into the atmosphere

nitrogen affects

shoot and root growth, shoot density, shoot color, hardiness, recuperative potential

chlorosis

overall pale yellow-green color that reflects reduction in chlorophyll production

N deficiency appears on the

lower leaves (non-mobile) eventually changing to yellow as symptoms progress

shoots have priority over roots for

available carbohydrates

carbohydrates stored in the roots are used to support

shoot growth

how are carbs replenished

by products resulting from photosynthesis

excessive amounts of N cause suppression of root growth and

carb reserves while shoot growth continues

excessive N rates restrict

depth and extent of root system, decrease nutrient and water uptake, decrease cell thickness, increase in cell size

decrease in shoot density may indicate

N deficiency

both a decrease and an excess of N results in

decreased hardiness, high N levels increase wilting

nitrate

NO₃^-

ammonium

NH₄^-

Nitrate is an

anion

nitrate is

mobile in the soil and can readily leach because soil has negative charge too

ammonium is a cation that may be bound in

a negatively charged medium like soil that tends to form an acidic medium when used

what is the role of N in the plant

has a role in substances such as proteins, amino acids, chlorophyll, nucleic acids, nucleotides, nucleosides

ammonium fixation is strongly absorbed to

negatively charged clay particles, especially 2:1 clays

ammonium and K compete for the

same selective binding sites on 2:1 clays

the amount and time of K fertilizer application are the most

important factors that govern the extent of fixation of NH₄⁺ fertilizer

when N and K fertilizers are applied simultaneously

there is a high amount of NH4+ fixation

most NH4+ fixation occurs when

potassium is added 7-10 days after NH4+

the least amount of NH4+ fixation occurs when the

potassium is added 7-10 days before NH4+ application

potassium before ammonium application results in

an increase of N uptake and plant yield

by adding potassium before ammonium, the potassium

occupies the fixing sites thus resulting in less ammonium being fixed

nitrate (NO₃^-) is easily

leached since most soils have a negative charge

generally the NO3- content in drainage water is

100x higher than that of NH4+

ammonium fed plants

uptake is best in neutral medium, absorbed by roots and translocated as organic compounds

uptake of ammonium results in a net efflux of

H+ ions into the rhizosphere and a decrease in the rhizosphere pH