nutrients

how is nitrogen allocated within a leaf?

in C3 plants more is allocated to rubisco than C4 plants

this means in C4 plants there is more available for other uses such as soluble or ligh harvesting proteins, bioenergetics or others (more productive)

macronutrients

essential nutrients in plants required in large quantities

K, N, Ca, Mg, P, S

micronutrients

essential nutrients in plants required in small quantities

Cl, B, Fe, Mn, Zn, Cu, Ni, Mo

beneficial elements in plants

enhance performance in many plants but not necessarily essential

Si, Na, Co

soil pH and element availability

as pH changes so does available nutrients

ideal zone is between 6-7 pH

often in agriculture they lime the soil to increase pH in acidic zones, increasing natural nutrient availability and boosting the effect of fertilizer

nutrient limitation

slowing or stopping of metabolic processes due to insufficient availability of essential nutrients

major includes nitrogen and phosphorus

nitrogen availability

limiting in water

readily available in atmosphere - 78% but not available for plant uptake due to strong triple bond

lightning and symbiotic organisms create available 

forms include ammonium and nitrate (inorganic) and the available/organic form is only 2%

how do plants uptake nutrients?

via roots or atmosphere

symbiotic relationships - mychorrhizal fungi, rhizbium bacteria, frankia, cyanobacteria

carnivory, parasitic

phosphorus functions

major limiting in soils, not easily dissolvable

used fr DNA and RNA formation, energy storage and transportation (ATP)

mycorrhizae and root exudates facilitate uptake

nitrogen function

amino acids - proteins like rubisco, DNA, pigments like cholorphyll

often limiting factor for plant growth

ammonium

NH4+

free living n fixing bacteria in soil, decomposition of biomass by fungi and bacteria

can be toxic to plants, therefore immediately transferred to amino acids after uptake - cant tolerate large amounts

nitrate

NO3-

free living n fixing bacteria in soil, decomposition of biomass by fungi and bacteria, lightning

not toxic and can be stored in roots/shoots, but immediate transformation to amino acids post uptake

nitrogen cycle

nitrogen in the air is fixed by bacteria or lightning, or supplied by fertilizers

undergoes decomposition to soil organic matter then mineralization to become ammonium, from here it can either under nitrification to become nitrite and then nitrate, it can be released as ammonia, uptook by plants or it can be fixed/eroded to the soil

nitrate can also contribute to leaching, plant uptake, soil erosion, orimmobilization. denitrification converts back to N gas and then it is released as emissions in the air and the cycle continues

liebigs law of the minimum

one limiting nutrient will inhibit all others even if they have higher supply

the barrel represents plant growth or crop yield

fertilizer effects

how P and N fertilizers work together

max yield is when max P and max N is used

adaptations to limitations

symbiosis with microorganisms, resorption of nutrients from senescing leaves, investment into root biomass or branching

but can be energetically costly and therefore these environments are usually adapted to by stress tolerant species with low productivity

aboveground net primary productivity and limitations

observing how combinations of different nutrients effects global grasslands 

NPK has very limiting effects together

additionally temperature effects as colder environments have slower rates of decomp

deficiency

not enough nutrients available of a specific kind

changes depending on the nutrient

toxicity

when there is too much of a nutrient

higher amounts may cause growth restrictions

easier among micronutrients where only small amounts are needed in the first place

saline habitats

unique habitats with salt deposition, adapted vegetation etc

electrical conductivity, fluctuates throughout the year

salinity gradient

freshwater → brackish → saline (as you move inland)

impacts species composition

why is freshwater fresh?

always replenished by rain

where does salt come from?

on the coast could be due to runoff accumulation, seafloor openings, evaporation

inland could be from bedrock weathering, high evap/low leaching in arid climates, discharge of groundwater - irrigation in ag, road salting

glycophytes

salt sensitive species

halophytes

salt tolerant species

for example sea blite or foxtail barley

recretohalophytes

expel salt through specialized structures 

salt glands in the epidermis may pump out salt, or salt bladders under leafs may accumulate salt excreted in an external vacuole

aluminium toxicity

issue in acidic soils, caused by bedrock, leaching in rainy areas (boreal or tropics), acid rain, root exudation in the rhizosphere

as pH decreases the solubility will increase

excluding Al

proposed research suggesting that root excretion of organic acids in roots across the plasma membrane to the apoplast (cell wall) then results in chelation of Al in the rhizosphere to the cell walls

aspen excluding al

may increase concentrations of citrate, malate and oxalate when Al concentrations increase

common in boreal and tropical forests

Al tolerance

chelation in cytosol (pulls into symplast), sequestration to vacuoles and then activation of tolerant metabolic pathways

triggers stress in cells

stressful environments

provide unique areas that result in biodiversity hotspots

ex in the cerrado ecoregion in brazil there are grasslands and savannas that are nutrient poor and al rich

high diversity and endemism - new niches, natural selections

ex bedrock meadows 

nutrient poor soils, high al concentrations due to bedrock

biodiversity hot spots but have low productivity