CRSS 4590 Exam 3

What is the main form of sulfur being taken up by the roots?

SO4 2- (sulfate)

Leaves can take up small amounts of what form of sulfur and what is it a by-product of?

leaves can take up small amounts of SO2 which is a byproduct of coal combustion

How is sulfur transported into cells?

co-transported into cells by symporters (3 H+)

Is sulfur mobile or immobile?

low mobile nutrient

What does it mean when you say sulfur is a low mobile nutrient?

the phloem transport from older to younger leaves is slow, and sulfur is not quickly moved form sites of storage when there is a deficiency

what helps sulfate move across membranes?

sulfur transported help move sulfate across membranes

Where does sulfur accumulate for storage?

sulfate can accumulate in large amounts in vacuoles

can stored sulfate support new growth?

no, stored sulfate is released too slow to support new growth

where does sulfur reduction (assimialtion) occur?

sulfur reduction occurs in chloroplasts and plastids in the roots

Explain sulfate assimilation

sulfate assimilation is a multistep process. first sulfate reduction takes place where sulfate is converted to sulfite. then sulfite reductase takes place where sulfite is converted to sulfide. then sulfide gets converted to cysteine which is an amino acid.

function of sulfur in plants

-amino acid production

-flavor such as the flavor in onions, cabbages, and mustards

are soils in vidalia used for growing vidalia onions high or low in sulfur?

low in sulfur

what are the symptoms of sulfur deficiency?

-chlorosis on younger leaves or whole plant

-may resemble N deficiency

When is sulfur toxicity a concern?

high level of SO2 (sulfur dioxide) in the air are toxic to plants

what are the acute symptoms of sulfur toxicity?

membrane disruption and necrosis

what are the chronic symptoms of sulfur toxicity?

Sulfite accumulation in leaves, chlorosis, growth and yield reduction, early senescence

are tree or herbaceous plants more sensitive to sulfur toxicity?

trees

sulfur cycle

-organic sulfur undergoes mineralization and releases sulfur in solution

-also has atmospheric cycle with sulfur dioxide

why is sulfur much more available than phosphorus?

because phosphorous is adsorbed

how much sulfur in the soil is organic matter?

95%

what type of organic sulfur is in arid regions?

sulfate salts such as gypsum

forms of organic sulfur in soils

-sulfate salts such as gypsum

-pyrite

what is the mineral form of sulfur taken up by plants?

sulfate

forms of inorganic sulfur in soil

-soil solution sulfur (sulfate)

-adsorbed sulfur (sulfate)

-sulfur coprecipitated with CaCO3

-reduced inorganic sulfur (sulfite and 0 charge sulfur)

does sulfate use diffusion or massflow to roots?

diffusion to roots if <3 mg/L and massflow to roots if >5 mg/L

is nitrate of sulfate leached more?

nitrate

what does sulfate adsorb to?

sulfate os an anion so adsorption is made by compounds with positive charges such as oxides and organic matter

will sulfur with monovalent cations or divalent cations leach more?

monovalent cations will leach more because it is adsorbed less strongly than divalent cations

will K2SO4 or CaSO4 leach more?

K2SO4 will leach more than CaSO4

What happens with sulfate and a low pH?

with a low pH you start getting more positive charges on OM and adsorption

sulfur adsorption decrease with?

sulfur adsorption decreases with increasing pH because positive charges are decreasing with increasing pH

what is sulfate being adsorbed by?

positive charges in clays and OM

why is there not a lot of sulfur in vidalia onion regions?

because sulfur gets stuck in lower regions of soil because of the low pH

sulfur precipitates with?

calcium

the availability of sulfur that is percipitaed with calcium increase when?

pH decreases because CaCO3 is more soluble

S2- (sulfite) accumulates under what condtions?

anaerobic conditions (waterlogged soils)

what happens with sulfur in waterlogged soils?

sulfide can react with iron and from metal sulfides like FeS2 (pyrite)

when is pyrite an issue?

-pyrite is not a problem until you try to drain waterlogged area and as you drain you get more oxygen and pyrite oxidizes and the pH drops fast

-when waterlogged areas are drained you have to add lime or it will kill everything due to the low pH

S0 (elemental sulfur) is oxidized by what and to what?

S0 is oxidized by microorganisms to sulfate and this is a biological reaction

in soils that are not waterlogged what happens to organic sulfur?

organic S is converted to sulfide and then S0 and then with enough oxygen to sulfate

organic sulfur is mineralized to what under anoxic conditions?

S2- (sulfide)

organic sulfur is mineralized to what under aerobic conditions?

SO4 2- (sulfate)

organic sulfur to sulfate is?

mineralization

sulfate to organic sulfur is?

immobilization

when is there a net mineralization or immobilization of sulfur?

there is a net mineralization of sulfur when the C/S ratio is <200 and there is a net immobilization when the C/S ration is >400

what is sulfur volatilization?

So2 is released into the air by industries and combustion of fossil fuels and then it is converted to sulfate

why is sulfur deficiency the next deficiency we may need to worry about particularly in the NE US?

because less sulfur is coming down due to no S in fertilizers, cleaning up acid rain, and less S in pesticides

sources of organic S

manures

sources of synthetic inorganic S

-elemental sulfur

-sulfuric acid

-gypsum

-aluminum sulfate

-ammonium polysulfide

-ammonium thiosulfate

-potassium sulfate

-ammonium sulfate

How is gypsum sourced?

can mine gypsum in nature or produce gypsum through flue gas desulfurization

what is the difference between mined and industrial gypsum?

industrial gypsum dissolves faster than mined gypsum

potential problems with gypsum

can lead to potential leaching of Mg and K because you need a cation to move with gypsum

gypsums affect of acid subsoils

-increases soluble Ca2+

-reduces toxic Al3+

-improves root proliferation

-avoids drought stress

-improves productivity

-may induce K and Mg deficiencies

-increases SO4- may cause loss of NO3-

what is used in nursery crops to acidify soils?

aluminum sulfate

what forms of sulfur acidify soils?

-aluminum sulfate

-ammonium polysulfide

-ammonium thiosulfate

will gypsum produce acidity?

no

what form of calcium is adsorbed?

Ca++

what is calcium transport driven by?

transpiration

is calcium mobile or immobile?

very immobile in the phloem

why is calcium immobile in the phloem?

calcium is immobile in the phloem because the phloem cells are connected by sieve plates and calcium in the phloem results in the production of callose, which blocks the sieve plates which therefore blocks transport in the phloem

how is calcium compartmentation achieved?

achieved by a variety of Ca-transporters, including ATP pumps, anti-porters, and channels

where is calcium stored?

can be stored in many areas including the vacuole, ER, and chloroplast but needs lots of different Ca transporters for this

functions of Ca in the plant

-provides stability and integrity to membranes

-important component of cell walls

-needed for cell elongation

-metabolic processes

How does calcium play a role in metabolic processes?

proteins bind to calcium (calmodulin) and calmodulin is only active when associated with four Ca2+ ions

calcium deficiency

-membranes may become leaky

-cells lose structural integrity

-mainly in meristematic tissue, fruits, and storage organs

-bitter pit or cork spot in apple

-blossom end rot in tomato

-tip burn in lettuce

what can cause calcium deficiency?

-drought conditions due to reduced transpiration

-high K+ and NH4+ can reduce Ca uptake and translocation

calcium toxicity

calcium can inhibit uptake of potassium

K+and NH4+ reduce uptake of what elements?

Ca and Mg because having an excess of one cation can interfere with the uptake of other cations

What else can reduce Mg uptake?

low pH

How is magnesium transported?

channels for root uptake; antiporter for vacuole storage

is magnesium mobile or immobile?

very phloem mobile

what is a difference between calcium and magnesium?

-calcium is very immobile while magnesium is very mobile

-magnesium will be remobilized when deficient and calcium will not

functions of magnesium

-component of chlorophyll molecule

-needed for photosynthesis

-crucial in many enzymatic reactions

how is magnesium stored?

stored in seeds as Mg phytate

how is magnesium crucial in enzymatic reactions?

-binds to ATP proteins

-many enzymes need Mg++ (rubisco)

magnesium deficiencies

-decrease in photosynthetic activity

-appear in older leaves first

-interveinal chlorosis

in highly weathered soils is there high or low Ca and Mg?

low Ca and Mg

why is there low Ca and Mg is highly weathered soils?

in highly weathered soils they can become acidic and you get aluminum so you have low Ca and Mg

what are the forms of Ca and Mg in soil?

-primary minerals

-soil solution

-exchangeable Ca and Mg

is Ca moved by diffusion of mass flow to the roots?

mass flow

is calcium usually high or low in soil?

high

is Mg moved to the roots by diffusion or mass flow?

mass flow

explain CEC and Ca and Mg

the higher the CEC the more Ca and Mg you expect

do 2:1 clays require higher or lower Ca and Mg saturation that 1:1 clays for similar availability to plants?

higher

high levels of what can reduce availability of Mg?

K+ and NH4+

when is the availability a problem in terms of availability?

in tropical soils that are very weathered

larger CEC means what for Ca and Mg?

more Ca and Mg

at a low ph what happens to Ca and Mg?

Al3+ competes with Ca2+ and Mg2+ for space on the CEC

if dolomitic limestone is used what happens to Mg?

can get high Mg

sources of Ca (fertilizers)

-CaCO3 and other liming agents

-CaSO4

-single and triple superphosphate

Which Ca fertilizers raise pH?

CaCO3

sources of Mg (fertilizers)

-dolomite

-Sul-Po-Mag

-MgCl2, Mg(NO3)2

which Mg fertilizers raise pH?

dolomite

how is iron taken up in non-grasses (strategy 1)?

ATP-ases that are sitting on the plasma membrane are pumping protons from inside of cell into the rhizosphere and as the proton concentration increases in the rhizosphere the pH starts decreasing and the lower pH increases solubility of iron. the increases solubility makes the ferric form of iron more available and then the FRO2 protein reduces the ferric form into the ferrous form and then the ferrous form is taken into the cells by iron transporters

how is iron taken up in grasses (strategy 2)?

PS binds and solubilizes the ferric form of iron and then the entire complex is brought into the cell using a transporter and once in the cell the iron can be removed from PS

how is iron taken up in rice (combination strategy)?

-rice can use both the ferric and ferrous form of iron

-same process as grasses for ferric form

-Iron transporters move ferrous form into cells

where is most of Iron in the cells?

chloroplast used for photosynthesis

where is the remaining iron that is not in the chloroplast?

mitochondria used for oxidation-reduction actions

what two major processes is iron involved in?

photosynthesis and oxidation-reduction actions

is iron immobile or mobile?

not very mobile and deficiency symptoms appear in younger leaves